Download Workshop, Previous Day 4 ITG International Vacuum Electronics Workshop 2014

4th ITG International Vacuum Electronics Workshop 2014
October 13 – 14, 2014, Physikzentrum Bad Honnef (www.pbh.de), Germany
Workshop, Previous Day
Sunday, October 12, 2014
15:30
ITG(VDE)-Fachausschuss 8.6 “Vakuumelektronik und Displays”,
124th Meeting
Physikzentrum Bad Honnef (PBH), Sitzungszimmer: Wintergarten
18:30
Start of the ITG Workshop for all participants:
Come Together Dinner & Evening Discussion,
Physikzentrum Bad Honnef: Lichtenberg-Keller (at basement level)
Workshop Program, 1st Day
Monday, October 13, 2014
Location: Wilhelm und Else Heraeus Hörsaal
08:30 Welcome Address: Wolfram Knapp, Workshop Chairman
Session 1.1: Vacuum Measurements and Vacuum Electronics in
Plasma Applications
Chairman: Wolfram Knapp
08:40 PROGRESS IN VACUUM PRESSURE MEASUREMENT
Wüest1
L1.1-1 Martin
1
INFICON Ltd, Alte Landstr. 6, LI-9496 Balzers, Liechtenstein
09:05 REDUCTION OF GAS-SPECIES DEPENDENCY OF VACUUM GAUGE
L1.1-2 SYSTEMS BY AN AUTOMATED SOFTWARE CALIBRATION PROCEDURE
Florian Dams1, Rupert Schreiner1
1
OTH Regensburg, Seybothstr. 2, D-93053 Regensburg, Germany
09:30 INVESTIGATIONS ON APPLICATION POTENTIAL OF PULSED ELECTRON
L1.1-3 BEAM DEPOSITION
Sebastian Schmidt1, Benjamin Graffel1, Falk Winckler1, Björn Meyer1, Gösta Mattausch1,
Frank-Holm Rögner1
1
Fraunhofer Institute for Electron Beam and Plasma Technology FEP, Winterbergstr. 28,
D-01277 Dresden, Germany
09:55 HIGH TEMPERATURE FURNACE AND PLASMA CHAMBER REACTION
L1.1-4 MONITORING USING INFICON CPM RESIDUAL GAS ANALYZER
Kenneth Wright1, Phillip Mach2, Guido F. Verbeck2
1
INFICON Inc., 2 Technology Pl., East Syracuse, NY 13057, USA,
2
Dept. of Chemistry, University of North Texas, 1155 Union Circle, Denton, TX 76203, USA
10:20
Coffee Break
Session 1.2: Field Emission Cathodes and Applications (I)
Chairman: Hans W. P. Koops
10:50 CHARACTERIZATION AND PROPERTIES OF PLANAR FIELD EMISSION
L1.2-1 CATHODES
Oliver Gröning1
Swiss Federal Laboratories of Material Testing and Research, Empa, CH-8600 Dübendorf,
Switzerland
1
11:15 SPECTROSCOPY OF PULSED LASER EXITED AND FIELD EXTRACTED
L1.2-2 ELECTRONS
S. Mingels1, V. Porshyn1, G. Müller1
1
FB C Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany
11:40 SUITABILITY OF CARBON-BASED NANOSTRUCTURES FOR VARIOUS
L1.2-3 COLD CATHODE APPLICATIONS
Pavel Serbun1, Günter Müller1
1
FB C Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany
12:05 FABRICATION, SIMULATION AND CHARACTERIZATION OF HIGH
L1.2-4 ASPECT RATIO SILICON TIP CATHODES
Christoph Langer1, Robert Lawrowski1, Christian Prommesberger1, Florian Dams1, Pavel
Serbun2, Michael Bachmann3, Günter Müller2, Rupert Schreiner1
1
OTH Regensburg, Seybothstr. 2, D-93053 Regensburg, Germany,
2
FB C Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany,
3
Ketek GmbH, Hofer Str. 3, D-89737 München, Germany
12:30
Lunch
Session 1.3: X-Ray Tubes and Gyrotrons (I)
Chairman: Günter Kornfeld
13:30 BUNCHED ELECTRON EMISSION FROM GRAPHENE EMITTERS WITH
L1.3-1 GaAs PHOTOSWITCH
O. Yilmazoglu1, S. Al-Daffaie1, F. Küppers1, H. L. Hartnagel1, Y. Neo2, H. Mimura2
1
Technische Universität Darmstadt, D-64283 Darmstadt, Germany,
2
Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan
13:55 FIELD EMISSION INITIATED GLOW DISCHARGE WITH LONG PULSES
L1.3-2 AND HIGH CURRENTS
Daniela Wenger1,3, Wolfram Knapp2, Bernhard Hensel3, Sandro F. Tedde1
1
Siemens AG, Corporate Technology, D-91058 Erlangen, Germany,
2
IFQ, Otto von Guericke University of Magdeburg, D-39106 Magdeburg, Germany,
3
MSBT, University of Erlangen-Nuremberg, D-91054 Erlangen, Germany
14:20 STATUS AND PROSPECTS OF GYROTRON DEVELOPMENT AT KIT:
L1.3-3 2014 UPDATE
J. Jelonnek1,2, K. A. Avramidis1, J. Franck1, G. Gantenbein1, K. Hesch3, S. Illy1, J. Jin1, P.
Kalaria1, A. Malygin1, I. Gr. Pagonakis1, T. Rzesnicki1, S. Ruess1,2, A. Samartsev1, A.
Schlaich1, T. Scherer4, D. Strauss4, M. Thumm1,2, C. Wu1, J. Zhang1
Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany,
1
IHM, 2IHE, 3KIT Nuclear Fusion, 4IAM-AWP
14:45 DESIGN ASPECTS FOR DEMO-COMPATIBLE 2 MW GYROTRONS:
L1.3-4 ELECTRON GUN AND CAVITY
J. Franck1, K. A. Avramidis1, S. Illy1, J. Jelonnek1, I. Gr. Pagonakis1, M. Thumm1
Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of
Technology (KIT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen,
Germany
1
15:10
Coffee Break
Session 1.4: Gyrotrons (II)
Chairman: Ernst Bosch
15:40 CONVENTIONAL CYLINDRICAL-CAVITY GYROTRON DESIGN FOR
L1.4-1 DEMO
P. Kalaria1, K. A. Avramidis1, J. Franck1, S. Illy1, J. Jelonnek1, I. G. Pagonakis1, M. Thumm1
1
Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of
Technology (KIT), D-76131 Karlsruhe, Germany
16:05 SECONDARY ELECTRON EMISSION MODEL IN THE CODE
L1.4-2 ESRAY&ESPIC
J. Zhang1, S. Illy1, I. Gr. Pagonakis1, J. Jelonnek1, M. Thumm1
1
Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of
Technology (KIT), D-76131 Karlsruhe, Germany
16:30 DEVELOPMENT AND OPTIMIZATION OF AN INVERSE MAGNETRON
L1.4-3 INJECTION GUN FOR FUTURE FUSION GYROTRONS
S. Ruess1,2, K. A. Avramidis1, G. Gantenbein1, S. Illy1, J. Jelonnek1,2, I. Gr. Pagonakis1, T.
Rzesnicki1
Karlsruhe Inst. of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany,
1
Institute for Pulsed Power and Microwave Technology (IHM)
2
Institute of High Frequency Techniques and Electronics (IHE)
16:55 INITIAL STEPS TOWARDS MULTI-STAGE COLLECTORS FOR
L1.4-4 GYROTRONS
Chuanren Wu1, K. A. Avramidis1, G. Gantenbein1, S. Illy1, J. Jelonnek1,2, I. Gr. Pagonakis1,
M. Thumm1,2
Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany
1
Institute for Pulsed Power and Microwave Technology (IHM)
2
Institute of High Frequency Techniques and Electronics (IHE)
18:30
Workshop Dinner & Evening Discussion
Physikzentrum Bad Honnef: Lichtenberg-Keller (at basement level)
Workshop Program, 2nd Day
Tuesday, October 14, 2014
Location: Wilhelm und Else Heraeus Hörsaal
Session 2.1: Vacuum Interrupters and Pulsed Power Switching
Chairman: Gösta Mattausch
08:40 COMBINED EXPERIMENTAL AND THEORETICAL STUDY OF
L2.1-1 CONSTRICTION THRESHOLD OF LARGE-GAP AMF VACUUM ARCS
N. Wenzel1, A. Lawall2, U. Schümann2, S. Wethekam3
Siemens AG, Germany
1
Corporate Technology, Günther-Scharowsky-Str. 1, D- 91058 Erlangen,
2
Infrastructure & Cities, Low & Medium Voltage Division, Rohrdamm 88, D-13629 Berlin,
3
Energy Sector, Power Transmission Division, Nonnendammallee 104, D-13629 Berlin
09:05 NEW ULTRA FAST EARTHING SWITCH (UFES) DEVICE BASED ON
L2.1-2 VACUUM SWITCHING PRINCIPLE
Dietmar Gentsch1
1
ABB AG, Calor Emag Medium Voltage Products, Oberhausener Str. 33,
D-40472 Ratingen, Germany
09:30 DIELECTRIC TESTING OF HV VACUUM INTERRUPTERS DURING
L2.1-3 CAPACITIVE CURRENT SWITCHING
B. Baum1, H. Janssen1, V. Hinrichsen1
1
Technische Universität Darmstadt, High Voltage Laboratories, D-64283 Darmstadt, Ger.
09:55 TRIGGERED SPARK GAP WITH INTERNAL TRIGGER DELAY CIRCUIT
Däumer1, Peter Bobert1, Frank Werner1
L2.1-4 Wolfgang
1
EPCOS AG, A TDK Group Company, Rohrdamm 88, D-13629 Berlin, Germany
10:20
Coffee Break
Session 2.2: Fundamentals in Vacuum Electronics,
HEMP Thrusters and Klystrons
Chairman: Andreas Lawall
10:50 GIANT CURRENT DENSITY IN KOOPS-GRANMAT - IS IT DUE TO A BEC
L2.2-1 CONDENSATE AT ROOM TEMPERATURE?
Hans W. P. Koops1
1
HaWilKo GmbH, Ober-Ramstadt Germany
11:15 SELF-SCREENING EFFECT OF INDIVIDUAL CNT FIELD EMITTER WITH
L2.2-2 HIGH ASPECT RATIO
Wolfram Knapp1
IFQ, Otto von Guericke University of Magdeburg, D-39106 Magdeburg, Germany
1
11:40 A FULLY KINETIC AND SELF-CONSISTENT SIMULATION OF A HEMPL2.2-3 THRUSTER USING A STATISTICAL APPROACH FOR SOLVING THE
“ANOMALOUS ELECTRON TRANSPORT” PROBLEM
Günter Kornfeld1
1
Kornfeld Plasma & Microwave Consulting, D-89275 Elchingen, Germany
12:05 X-BAND HOLLOW-BEAM KLYSTRON DESIGN WITH CORKSCREWL2.2-4 MODULATION
Jiwei Nie1, Heino Henke1, André Grede2
1
Technische Universität Berlin, Sekr. EN-2, Einsteinufer 17, D-10587 Berlin, Germany,
2
Hüttinger Elektronik, Boetzinger Str. 80, D-79111 Freiburg, Germany
12:30
Lunch
Session 2.3: Traveling Wave Tubes (TWTs)
Chairman: Manfred Thumm
13:00 BROADBAND TRAVELING WAVE TUBES IN Ka- GRANTS MODERN
L2.3-1 COMMUNICATION
E. Bosch1, A. Laurent1, P.Ehret1, Jean Gastaud1
1
THALES Electron Devices, 78141 Vélizy, France, and D-89077 Ulm, Germany
13:25 THALES 150 W C-BAND TRAVELLING WAVE TUBES
1
1
1
1
L2.3-2 W. Dürr , C. Dürr , P. Ehret , E. Bosch
Thales Electronic Systems GmbH, Söflinger Str. 100, D-89077 Ulm, Germany
13:50 BEAD-PULL MEASUREMENT OF A W-BAND FOLDED WAVEGUIDE
L2.3-3 STRUCTURE
Heinrich Büssing1, André Grede2, Heino Henke1
1
Technische Universitat Berlin, Sekr. EN-2, Einsteinufer 17, D-10587 Berlin, Germany,
2
Hüttinger Elektronik, Boetzinger Str. 80, D-79111 Freiburg, Germany
14:15 SIMULATION OF BEAM-WAVE INTERACTION IN FILTER-TYPE SLOW
L2.3-4 WAVE STRUCTURES OF TRAVELLING WAVE TUBES
Philip Birtel1, Elke Gehrmann2, Sascha Meyne2, Arne F. Jacob2
1
Thales Electron Devices, Söflinger Str. 100, D-89077 Ulm, Germany,
2
Technische Universität Hamburg-Harburg, Institut f. Hochfrequenztechnik, D-21073
Hamburg, Germany,
14:40 HOT MATCHING ANALYSIS OF A GENERIC TWO-SECTION COUPLEDL2.3-5 CAVITY TRAVELING-WAVE TUBE
Sascha Meyne1, Jean-François David2, Arne F. Jacob1
1
Institut für Hochfrequenztechnik, Technische Universität Hamburg-Harburg, Hamburg,
2
Germany,
Thales Electron Devices, Vélizy, France
15:05
Closing Words: Manfred Thumm, Workshop Co-Chairman
15:15
Coffee Break
→ End of Workshop: 16:00
PROGRESS IN VACUUM PRESSURE MEASUREMENT
1
Martin Wüest1
INFICON Ltd, Alte Landstrasse 6, LI-9496 Balzers, Liechtenstein
ABSTRACT
For many years standard vacuum pressure measurement sensors consist of capacitance
diaphragm gauges, Pirani heat transfer gauges as well as ionization gauges. Development
has progressed from passive gauges with a detached controller to combination gauges with
integrated electronics. Market demand from the semiconductor industry continues to force
the development of smaller, cheaper and better process sensors. Better in this context
means the sensors must survive the harsh process conditions for longer, measure faster and
with better reproducibility. I will present some of the recent developments.
Reduction of Gas-Species Dependency of Vacuum Gauge Systems by an
Automated Software Calibration Procedure
Florian Dams1, Rupert Schreiner1
OTH Regensburg, Seybothstrasse 2, D-93053 Regensburg, Germany
1
Topic: A3 Vacuum Microelectronic and Nanoelectronic Devices
Preferred Presentation Form: P Poster Presentation
ABSTRACT
For vacuum pressure measurement different measurement principles are necessary due to the large range
of the pressure regime of several orders of magnitude. In rough vacuum pressure can be measured
independent of the species of the residual gas by membrane gauges. Gauges with measurement principles
that are well suited for lower pressure regimes produce a signal that also depends on the gas species.
Such gauges like thermal conductivity (“Pirani”) or ionization vacuum gauges are calibrated for nitrogen
and the pressure value has to be corrected by gauge specific calibration curves of the used gas [1, 2].
In common vacuum applications different gauges are used to cover a specified pressure region. If the
signal of one gauge in the system is gas species independent it can be used to calibrate the other one in
the overlap region of their measurement ranges [3]. By such a procedure the gas species dependency of
the system is significantly reduced if the gas composition does not change below the calibration pressure
[4].
In this work we present such an automated in-system calibration procedure with a system consisting of
MEMS-based Pirani gauge [5] as gas species dependent sensor and a gas species independent membrane
gauge. The dependence of the characteristic curve on the gas type of the Pirani gauge can be described
analytically. Furthermore due to the miniaturized geometry of the sensor there is a significant overlap of
the measurement region with that one of gas species independent gauge. During pumping down the
calibration curve of the Pirani vacuum gauge is calculated by a microcontroller based on the signal of the
membrane gauge. Afterwards the fit parameter of this curve are used for calibration of the thermal
conductivity vacuum gauge. By this way the gas species dependency of the system was significantly
reduced.
References
[1] K. JOUSTEN, J. Vac. Sci. Technol. A 26, 352 (2008).
[2] R.E. ELLEFSON and A.P. MIILLER, J. Vac. Sci. Technol. A 18, 2568 (2000).
[3] H. PLÖCHINGER, Patent DE19860500 A1 (2000)
[4] F. DAMS and R. SCHREINER, in Proceedings of the 8th International Conference & Exhibition on
Integration Issues of Miniaturized Systems, Vienna, April 2014, edited by T. Gessner (Apprimus,
Aachen, 2014) p. 459.
[5] F. DAMS and R. SCHREINER, J. Vac. Sci. Technol. A 32, 031603 (2014).
Investigations on application potential of Pulsed Electron Beam Deposition
Sebastian Schmidt1, Benjamin Graffel1, Falk Winckler1, Björn Meyer1,
Gösta Mattausch1, Frank-Holm Rögner1
1
Fraunhofer Institute for Electron Beam and Plasma Technology FEP
Winterbergstraße 28, 01277 Dresden, Germany
ABSTRACT
This paper presents the Pulsed Electron Beam Deposition (PED) process, a new field of work at FEP.
This was enabled by a special electron beam source recently developed and delivered by Organic
Spintronics srl. Its function principle relies on a channel-spark discharge. The source generates a shortpulsed, polyenergetic electron beam with a very high power density ≥( 108 W/cm² over some
nanoseconds). When directed to a target, the surface of the material is locally heated to an extent that
ablation occurs, with subsequent propagation of the vapour towards the substrate in a directional
flow [1]. As opposed to classic EB-PVD (Electron Beam Physical Vapour Deposition), the source
material to be evaporated remains solid in PED. The advantage is that this allows for homogeneously
depositing alloys in the proper stoichiometric ratio, because there is no accumulation of the less-volatile
components due to the avoidance of a molten bath. Furthermore, the coating rate can be precisely
adjusted facilitated by defined energy pulses. When compared to alternative Pulsed Laser Deposition
(PLD), PED excels by lower system costs in case of industrial application. An essential feature of the
PED process includes its high variability: nearly all materials (both electrically conductive and
insulating materials) may be ablated, and the energy utilization efficiency is high. The undesired
deposition of micro-particles (“droplets”) during layer formation can be suppressed by optimizing the
process parameters. Beneficial particularities of PED include the formation of dense discharge plasma.
It increases the energy of the ablated particles to some 10 eV at a degree of ionization of vapour
particles of 30…70 % and thus to a higher energy level than reached during EB-PVD or sputtering, for
example. This positively influences the properties of the growing layers so that the substrate
temperature can be kept low. Therefore, the growing of well-adhering, dense layers is also made
possible on temperature-sensitive substrate materials – such as p lastics. Moreover, reactive process
control is possible by adding the corresponding gases. As a result, there are numerous different
application possibilities like the production of hard material layers, decorative layers, or transparent,
conductive oxide layers. Further potential applications can be found in the field of flexible displays and
in the domain of heterostructured thermoelectric materials. The first tests of the new source at FEP were
intended to develop a general understanding of the PED process, as well as to investigate the suitability
of the method for different applications. For instance, the deposition of thin metal and semiconductor
layers was examined in process chains for photovoltaic applications. Furthermore, promising trials
regarding the deposition of transparent conductive oxide layers as well as i nsulating layers were
conducted.
References
[1] G. MUELLER, M. KONIJNENBERG, G. KRAFFT, and C. SCHULTHEISS. Thin Film Deposition
by Means of Pulsed Electron Beam Ablation. in: F.C. MATACOTTA and G. OTTAVIANI (eds).
Science and Technology of Thin Films. World Scientific Publishing Co. Pte. Ltd., 1995, pp. 89-119
Preferred form of presentation: O
High Temperature Furnace and Plasma Chamber Reaction Monitoring Using INFICON CPM
Residual Gas Analyzer
Kenneth Wright1, Phillip Mach2, and Guido F. Verbeck2
1
INFCION Inc., East Syracuse, NY USA
2
Dept. of Chemistry, University of North Texas, Denton, TX USA
ABSTRACT
Residual gas analyzers continue to be of value in monitoring semiconductor manufacture and
other process treatments. Extending this technology and the ability of INFICON’s RGA
based Compact Process Monitor (CPM) to provide meaningful data in measuring gas phase
reactions, recognizing trace level analyte contaminants, and qualifying gas purity to plasma
chamber reactions and in high temperature furnaces in situ has proved the effectiveness of
using this instrumentation beyond process monitoring. Experiments observing the
carbothermal reduction mechanisms of Yttria-Stabilized Zirconia (YSZ) have yielded insights
into determining whether carbon dioxide (CO) is the driving force behind conversion of ZrO2
to ZrC. The reaction products were analyzed in real time, in conjunction with temperature
program data, to provide insight into reaction mechanisms. Furthermore, the CPM was used
in monitoring plasma process reactions. Gas analysis of downstream plasma effluent yields
insight into plasma precursor dissociation and molecule species creation. The use of the CPM
in observing plasma treatment of carbon nanotubes and post reaction effluent gases from them
has provided insight into new nanotube gas absorbing mechanisms. The extension from
process monitoring to observing plasma and high temperature reactions is a novel step
forward in using the CPM, ultimately this will provide new insights into various progressive
techniques. The design, performance, and recent advances towards the next generation CPM
will also be discussed.
Characterization and Properties of Planar Field Emission Cathodes
Oliver Gröning
nanotech@surfaces Laboratory
Swiss Federal Laboratories for Materials Testing and Research, Empa
CH-8600 Dübendorf
[email protected]
Abstract
The emission of electrons into vacuum by electric field induced tunneling is an elegant way to
produce beams of free electrons for various applications in imaging, displays, analytics or X-Ray
generation. The drawback of field emission is the circumstance, that the required electric fields
above 1 GV/m cannot be created in a controlled and reliable manner on a flat surface. Instead
the field enhancing effect of tip like metallic structures must be exploited to locally generate the
extraction field, which however reduces the actual emitting surface drastically and therefore
also the emitted current.
A way out of this problem is to use planer emitter arrays, where the emission current of a
device originates from multiple emission sites, where the emission current is scaled by the
density of emission sites. This approach has been pushed particularly in the context of the
development of field emission displays, where homogenous, large area electron emission is at
the heart of the device operation. In was also this context that shortcomings in the
characterization of field emission using simple diode setups have become apparent. In this
presentation we will discuss the particular difficulties of a meaning full characterization of
planar field emission cathodes and how these difficulties can be overcome using a local
scanning probe. The basic layout of the scanning anode field emission microscope (SAFEM) will
be presented and how this instrument can be used to acquire statistical evaluations of the
emission sites and their individual field emission properties on a planar field emission cathode
(e.g. a carbon nanotube cathode). As an example we will show and quantify experimentally and
theoretically ensemble effects like electrostatic shielding. We will then discuss how such data
can be used to develop a macroscopic emission model of the cathode and understand effects
like degradation and emission current limitation. Based on this discussion we will examine
different strategies for the improvement of field emission cathodes.
SPECTROSCOPY OF PULSED LASER EXITED AND FIELD EXTRACTED ELECTRONS
S. Mingels, V. Porshyn, G. Müller
FB C Department of Physics, University of Wuppertal, Wuppertal, Germany
Topic: Electron Sources and Electron Emission
ABSTRACT
In order to develop highly brilliant, pulsed electron sources based on photo-induced field emission
(PFE), which combines advantages of photo and field emission FE, a new measurement system was
constructed at BUW*. It can provide direct as well as indirect spectroscopy of electrons from cold
cathodes in a triode configuration under high electric fields (up to ~100 MV/m) by a recently installed
hemispherical spectrometer (resolution = 6.7 meV) and quantum efficiency QE measurements under
pulsed tuneable laser illumination (3.5 ns, 10 Hz, 0.5-5.9 eV, > 0.3 mJ), respectively. Moreover, a
comprehensive system upgrade was performed, which enables precise triode positioning, controlled
sample cooling or heating (77-400 K), and dust protected sample insertion. First tests of the apparatus
and the spectrometer commissioning were carried out with DC FE from a W tip resulting in a reliable
work function of 4.42 ± 0.19 eV compared to the literature value of 4.55 eV**. Further measurements
of pulsed spectra from flat PFE cathodes are planned and will be presented at the workshop.
* B. Bornmann et al., Rev. Sci. Instrum. 83, 013302 (2012)
** B.J. Hopkins and J.C. Rivière, Proc. Phys. Soc. 81, 590 (1963)
Suitability of carbon-based nanostructures for
various cold cathode applications
P. Serbun*, G. Müller
FB C Physics Department, University of Wuppertal, Wuppertal, Germany
Field emission (FE) cathodes are considered as attractive alternative to thermionic or
photo cathodes for the generation of high-current, low-emittance and ns-pulsed electron beams.
Bottom-up grown nanostructures like carbon nanotubes (CNT) and carbon nanowalls (CNW)
provide excellent electron field-emission (FE) properties due to their high aspect ratio.
Therefore, such cathodes have been optimized for a variety of vacuum device applications, e.g.
flat light sources, compact X-ray tubes and microwave amplifiers [1, 2, 3].
Nevertheless, actual CNT and CNW FE cathodes have some disadvantages that need to
be overcome in order to fully exploit their application potential. CNT suffer from poor contact
to the substrate, which result in high contact resistance, limited FE current and lifetime [4, 5].
Furthermore, the varying shape, random alignment and mutual shielding of CNT and CNW
often limit the homogeneity of such FE cathodes [6, 7] and cause low transmission efficiency of
triode structures.
Therefore, different approaches to improve the FE homogeneity, current density and
contact interface of structured carbon-based cathodes for diode and triode applications will be
presented and discussed at the workshop.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
J. Eichmeier, M. Thumm (Eds.), “Vacuum electronics: components and devices”,
Springer-Verlag Berlin Heidelberg (2008).
Y. Saito, “Carbon Nanotubes and Related Field Emitters”, Wiley-VCH, Weinheim
(2010).
A. N. Obraztsov, V.I. Kleshch, and E.A. Smolnikova, Beilstein J. Nanotechnol. 4, 493
(2013).
L. Nilson, O. Gröning, P. Gröning, and L. Schlapbach, App. Phys. Lett. 79, 1036 (2001).
S. Purcell, P. Vincent, C. Journet, and V. Binh, Phys. Rev. Lett., 88, 105502 (2002).
A. Navitski, G. Müller, V. Sakharuk, A.L. Prudnikava, B.G. Shulitski and V.A. Labunov,
J. Vac. Sci. Technol. B 28, C2B14-19 (2010).
A. Navitski, P. Serbun, G. Müller, R.K. Joshi, J. Engstler, and J.J. Schneider, Eur. Phys.
J. Appl. Phys. 59, 11302/1-6 (2012).
Area: Vacuum Electronic and Discharge Devices and their Applications
Topic: A3 Vacuum Microelectronic and Nanoelectronic Devices
Preferred Presentation Form: Talk
Fabrication, Simulation, and Characterization of High Aspect Ratio Silicon Tip Cathodes
Christoph Langer1, Robert Lawrowski1, Christian Prommesberger1, Florian Dams1,
Pavel Serbun2, Michael Bachmann3, Günter Müller2 and Rupert Schreiner1
1
OTH Regensburg, Seybothstraße 2, D-93053 Regensburg, Germany
2
University of Wuppertal, Gaußstraße 20, D-42097 Wuppertal, Germany
3
Ketek GmbH, Hofer Straße 3, D-81737 München, Germany
Topic: A3 Vacuum Microelectronic and Nanoelectronic Devices
Preferred Presentation Form: P Poster Presentation
ABSTRACT
Silicon field emission (FE) cathodes are promising candidates for the application in electron sources,
vacuum sensors and x-ray tubes. As presented in [1, 2] it is possible to fabricate very homogeneous ntype, p-type, and metal coated silicon tip arrays with a field enhancement factor in the range of 60 to
140. Based on these results, we improved our fabrication process using a combination of reactive-ionetching (RIE) and subsequent etching with an inductively-coupled-plasma (ICP). That additional step
allows us to realize sharp tip structures on top of elongated pillars. By simulations with COMSOL
Multiphysics® the geometric field enhancement factor β was calculated. Therefore, the elliptic curvature
shape model given in [3] was adapted to the new geometry of the emitters. N-type as well as p-type
silicon structures with a total height of ≈5 µm, a pillar height of ≈4.5 µm, a pillar diameter of ≈1 µm, an
aperture angle of ≈60°, and an apex radius less than 20 nm were fabricated. These FE cathodes were
characterized by field emission scanning microscopy [4] under ultra-high vacuum conditions. Integral
measurements of arrays with 271 tips showed low onset-fields of ≈10 V/µm and field enhancement
factors of up to 700 during up- and down-cycle. With n-type silicon structures the expected FNbehaviour was observed, whereas p-type silicon structures showed saturation region above ≈15 V/µm.
Compared to our previously fabricated Si-tip structures [1, 2] the saturation region is more pronounced.
The saturation behaviour can be explained by the limited number of electrons in the conduction band [5]
and a further carrier depletion effect caused by the pillars themselves [6]. At an operating point in the
saturation region a fluctuation of the emission current below ±2% was observed with p-type silicon tips
on pillars. That combination offers an excellent method to stabilize the emission current.
References
[1] F. DAMS, A. NAVITSKI, C. PROMMESBERGER, P. SERBUN, C. LANGER, G. MÜLLER,
R. SCHREINER, IEEE Trans. Electron Devices, vol. 59, pp. 2832–2837, 2012.
[2] P. SERBUN, B. BORNMANN, A. NAVITSKI, G. MÜLLER, C. PROMMESBERGER, C.
LANGER, F. DAMS, R. SCHREINER, J. Vac. Sci. Technol. B, vol. 31, pp. 02B101, 2013.
[3] C. LANGER, C. PROMMESBERGER, F. DAMS, R. SCHREINER, Proc. of IVNC 2012, pp. 148–
149, 2012.
[4] D. LYSENKOV, G. MÜLLER, International Journal of Nanotechnology, vol. 2, pp. 239, 2005.
[5] D. K. SCHRODER, R. N. THOMAS, J. VINE, H. C. NATHANSON, IEEE Trans. Electron Devices,
vol. 21, pp. 785–798, 1974.
[6] L. F. VELASQUEZ-GARCIA, S. A. GUERRERA, Y. NIU, A. I. AKINWANDE, IEEE Trans.
Electron Devices, vol. 58, pp. 1775–1782, 2011.
Bunched electron emission from graphene emitters with GaAs photoswitch
O. Yilmazoglu1*, S. Al-Daffaie1, F. Küppers1, H. L. Hartnagel1, Y. Neo2, H. Mimura2
1
Technische Universität Darmstadt, 64283 Darmstadt, Germany.
2
Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan.
*[email protected]
ABSTRACT
A simple photocathode for bunched electron emission was fabricated and used for field electron
emission in a diode configuration. Commercial graphene nanoplatelets were used as field emitter array
with low turn-on field. The graphene nanoplatelets have thicknesses in the range of 2-10 nm and a high
aspect ratio of 1000-2000. A low turn-on electric field of ~1.5 V/µm (defined at 1µA/cm2) was obtained
for this emitter. The photo-modulation was achieved with a GaAs photoswitch in series to the bottom of
the graphene emitters. The semi-insulating (s.i.) GaAs is a promising high-power and fast photoswitch
with high electron mobility (>6000 cm2/Vs), sub-nanosecond carrier lifetime [1] and high quantum
efficiencies. A single photoconductive GaAs switch in a planar configuration can handle currents and
voltages as high as 3.7 kA and 28 kV, respectively [2]. Furthermore, the s.i. GaAs has a high resistivity
of > 1 x 107 Ωcm and a high electric breakdown field of >2x104 V/cm.
A simple low-power low-cost external laser modulated the GaAs photoswitch. This photocathode
configuration can find applications in optically driven X-ray sources with high on/off ratio for X-ray
imaging. Initial field emission measurements showed an on/off ratio > 200 and modulation up t o
300 kHz (Fig.1). New photoswitches with very low carrier life-time can open further promising
applications in high-charge short-pulse electron sources to produce fast electron bunches for x-ray free
electron lasers as well as for miniaturized high frequency vacuum tubes.
The dc characteristics as well as fast photo-modulated field emission currents will be presented.
Furthermore, a future design optimization for contact pulsed X-ray sources will be presented.
Fig. 1 Photo-modulated field emission current from graphene with GaAs photoswitch.
References
[1] J. S. Weiner and P. Y. Yu, J. Appl. Phys. 55 (1984) 3889.
[2] W. Shi et al., Appl. Phys. Lett. 92 (2008) 043511.
Field Emission Initiated Glow
Discharge with Long Pulses and High Currents
D. Wenger1,3, W. Knapp2, B. Hensel3, S. F. Tedde1
1
Siemens AG, Corporate Technology, 91058 Erlangen, Germany
2
IFQ, University of Magdeburg, 39106 Magdeburg, Germany
3 MSBT, University of Erlangen-Nuremberg, 91054 Erlangen, Germany
ABSTRACT
Field emitters are a promising alternative for thermionic electron sources in X-ray tubes. However
the main challenges remain the achievement of stable and high field emission currents of more than
100 mA, even up to 1,5 A, with simultaneous current densities beyond 3 A/cm2.
Field emission (FE) properties of SWCNT/graphene hybrid samples were investigated in DC as
well as in pulsed mode. A transition of electron field emission to glow discharge was measured for
high currents, long pulse-on times or high duty cycles with stainless steel anodes. Pulse-on times
varied between 0.2 ms and 400 ms and duty cycles between 1% and 80%. DC measurements
showed a slow transition to glow discharge already at currents greater than 10 mA. The pulsed IVcharacteristics with up to 400 mA maximum current deviated also from the Fowler-Nordheim (FN)
behavior. Constant-voltage behaviour arises after subtracting the cathode resistance. This constant
voltage behavior, the observed glowing during field emission and time resolved measurements give
evidence for the transition from FN type field emission to FE enhanced glow discharge. FE enables
a soft transition to normal glow discharge without the need of an ignition voltage. The build-up
dynamic and the respective time constants of the glow discharge will be evaluated and discussed,
based on the observed data. Respective equivalent electric circuits for the FN-type field emission
and for the normal glow discharge will be presented.
Electron stimulated desorption (ESD) of stainless steel appears to be the most reasonable reason for
this transition causing a pressure increase in the gap between cathode and anode in the range that
glow discharge can be ignited. It was observed that almost no glow discharge occurs with copper or
molybdenum anodes. The outgassing of stainless steel is significantly higher due to the low thermal
conductivity and the high amount of ESD.
References
[1]
[2]
D. Wenger, W. Knapp, B. Hensel, and S. F. Tedde, “Transition of Electron Field Emission
to Normal Glow Discharge”, submitted 2014.
O. Malyshev, C. Naran, “Electron stimulated desorption from stainless steel at temperatures
between 15 and +70 C”, Vacuum 86, 1363 (2012).
STATUS AND PROSPECTS OF GYROTRON DEVELOPMENT AT KIT: 2014 UPDATE
J. Jelonnek1,2, K. A. Avramidis1, J. Franck1, G. Gantenbein1, K. Hesch3, S. Illy1, J. Jin1, P. Kalaria1,
A. Malygin1, I. Gr. Pagonakis1, T. Rzesnicki1, S. Ruess1,2, A. Samartsev1, A. Schlaich1, T. Scherer4,
D. Strauss4, M. Thumm1,2, C. Wu1, J. Zhang1
Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany
1
IHM, 2IHE, 3KIT Nuclear Fusion, 4IAM-AWP
ABSTRACT
KIT is performing gyrotron research and development for the two major plasma fusion devices under
construction in Europe, the stellarator Wendelstein 7-X (W7-X) at Greifswald, Germany [1] and the
international experimental nuclear fusion reactor ITER at Cadarache, France [2]. As part of the
European fusion development consortium (EUROfusion), KIT is contributing significantly to the
development of gyrotrons which shall fulfil the future needs of DEMO, the nuclear fusion demonstration
power plant that will follow ITER. Within that research and development, KIT is investing in the
development of advanced design tools, in components research, and in a proper test environment.
Both experiments, W7-X and ITER, are relying on electron cyclotron resonance heating (ECRH) as the
main heating method for steady state operation, while it is planned for ITER to additionally apply
electron cyclotron resonance technique for current drive (ECCD). Gyrotrons are the unique RF sources
which meet the extraordinary requirements of those applications: RF output power in the MW range,
operating frequencies up to 170 GHz, and pulse lengths of several seconds up to 1 h continuous wave
operation (CW). Optimum current drive efficiencies for future nuclear fusion devices such as DEMO
will require the development of gyrotrons operating at even higher frequencies (>200 GHz), offering
efficiencies better than 60 % together with multi-MW levels of RF output power [3]. To prevent
mechanical antenna steering close to the plasma, frequency step-tunable RF sources will be required for
localized plasma stabilization [4]. KIT is contributing to this development by doing theoretical studies
and experiments.
In this presentation, the latest status and prospects of the different developments will be presented.
Acknowledgement
This work has been supported in parts by the European Community, under the contract of Association
between EURATOM and Karlsruhe Institute of Technology (KIT) and within the framework of the
European Fusion Development Agreement (EFDA), or under the EUROfusion consortium. Other parts
have been supported by Fusion for Energy (F4E) under the contracts F4E-GRT-432 and F4E-OPE-458
to the European Gyrotron Consortium (EGYC). EGYC is a collaboration among CRPP, Switzerland;
KIT, Germany; HELLAS, Greece; IFP-CNR, Italy. The views expressed in this publication do not
necessarily reflect the views of F4E or the European Commission.
References
[1] V. Erckmann, et. al., Fusion Sci. & Techn. 52, 291, 2007,
[2] C. Darbos, et. al., 35th IRMMW-THz, Rome, Italy, 2010
[3] H. Zohm, M. Thumm, J. of Physics: Conf. Series, 25, 274-282, 2005
[4] E. Poli, et. al., Nuclear Fusion, 53, no. 10, 2013
DESIGN ASPECTS FOR DEMO-COMPATIBLE 2 MW GYROTRONS:
ELECTRON GUN AND CAVITY
J. Franck, K. A. Avramidis, S. Illy, J. Jelonnek, I. Gr. Pagonakis, M. Thumm
Institute for Pulsed Power and Microwave Technology (IHM), Karlsruhe Institute of Technology (KIT),
Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen
ABSTRACT
In a commercial power plant based on magnetic confinement fusion of deuterium and tritium, especially
the first demonstration plant DEMO to be commissioned around 2050, the plasma needs to be heated up
to above 108 K in order to obtain a sufficient fusion rate. The required heating power of tens of
megawatts [1] and an effective plasma control can be provided by gyrotrons in the form of microwave
radiation via electron cyclotron resonance heating and current drive (ECRH&CD). Physical and
economic considerations demand high unit power, reliability and efficiency per tube at an output
frequency significantly above 200 GHz for both pulsed and steady-state operation according to current
studies [1].
In this talk, a design approach towards a coaxial-cavity 2 MW gyrotron will be presented. The approach
includes mode-selection based on multi-frequency operability as well as the design of the cavity and of
the coaxial triode-type magnetron injection gun. Critical design restrictions due to the quasi-optical
output system and to the window of the gyrotron are already addressed within the mode-selection
scheme. Thus, the gyrotron is optimized for mode TE49,29, corresponding to a frequency of 237.5 GHz,
but would also allow operation at other modes with sufficient efficiency, such as TE42,25 (at 203.8 GHz
for e.g. plasma control), TE35,21 (170.0 GHz) or TE56,33 (271.3 GHz for e.g. pulsed DEMO operation).
Results from numerical electron gun [2] and interaction simulations [3,4] will be presented.
Acknowledgment
This work, supported by the European Communities under the contract of Association between
EURATOM and Karlsruhe Institute of Technology, was carried out within the framework of the
European Fusion Development Agreement. The views and opinions expressed herein do not necessarily
reflect those of the European Commission.
References
[1] E. POLI et al 2013 Nucl. Fusion 53 013011
[2] I. GR. PAGONAKIS, J. L. VOMVORIDIS Proc. 29th Joint Int. Conf. Infrared Millim. Waves, THz
Electron., Karlsruhe, Germany, 2004, pp. 657-658
[3] K. A. AVRAMIDES et al EPJ Web of Conferences 32, 04016 (2012)
[4] S. KERN wiss. Bericht des FZKA 5837, Karlsruhe 1997
CONVENTIONAL CYLINDRICAL-CAVITY GYROTRON DESIGN FOR DEMO
P. Kalaria, K. A. Avramidis, J. Franck, S. Illy, J. Jelonnek, I. Gr. Pagonakis, M. Thumm
Institute for Pulsed Power and Microwave Technology (IHM),
Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany
ABSTRACT
Based upon the experiences and results of the ITER experimental nuclear fusion reactor, a
demonstration power plant (DEMO) is proposed to be built to prove the technical and economic
feasibility of fusion energy. Electron Cyclotron Resonance Heating and Current Drive (ECRH&CD) of
the fusion plasma plays a key role in such a DEMO. The necessary mm-wave radiation is provided by
gyrotrons. To achieve sufficient fusion gain, it is desirable to use gyrotrons with frequencies around
240 GHz and electrical efficiencies higher than 60 %. Along with this, fast frequency tunability of
2-3 GHz and slow frequency tunability of 30 – 40 GHz (in a few seconds resp. minutes) is requested [1].
The use of broadband or step-tuneable single disk CVD diamond windows is proposed to achieve this
tuneability, while the beam interaction efficiency and the beam energy recovery system efficiency must
remain high to obtain the required efficiency. Along with conventional cavity gyrotrons, coaxial cavity
gyrotrons are being investigated at IHM, KIT to set the parameter space for the future gyrotron. The
design of the different gyrotron components (like interaction section, Magnetron Injection Gun (MIG),
Quasi-Optical Launcher (QOL) with the mirror box and multi-stage depressed collector (MDC)) is in
progress.
The following mode chain is suitable for the high-frequency, high-power conventional-cavity gyrotron
with good multi-frequency properties: TE19,7 (104 GHz) – TE25,9 (137 GHz) – TE31,11 (170 GHz) –
TE37,13 (203 GHz) – TE43,15 (236 GHz) – TE49,17 (267 GHz). At 236 GHz, the mode TE43,15 is selected
for optimization as cavity mode for the DEMO gyrotron. This vacuum tube would also support
170 GHz, TE31,11 mode operation for ITER and could be used for the ECCD system of a pulsed DEMO
version at 270 GHz. These modes possess the same caustic radius, thus the design of the QOL, mirrors
and the MIG fits for all these modes. The first three modes at 104 GHz, 137 GHz and 170 GHz have
been successfully operated by the JAEA gyrotron team [2].
The conventional cavity for the 236 GHz TE43,15 mode gyrotron is designed using the in-house
developed code package CAVITY. At high frequency (>200 GHz), the ohmic cavity wall loading is a
critical parameter for the cavity design. The physical parameters of the cavity are optimized such that
maximum output power and efficiency are achieved with the reasonable ohmic cavity wall loading of
2 kW/cm2. Single-mode and multi-mode self-consistent time-domain (SELFT) calculations predict
stable operation of the TE43,15 mode without serious competing modes for suitable start-up conditions.
The presentation will provide a comprehensive overview of the ongoing research which will lead to the
conventional-cavity gyrotron design for DEMO.
References
[1] M. Thumm, et al., in Proceedings of the 5th Int. Workshop on Far-Infrared Technologies (FIRT
2014), Fukui, Japan, 5-7 March 2014, p. 5-7.
[2] Y. Oda, K. Kajiwara, et al., EPJ Web Conferences 32, 04004, 2012.
Secondary electron emission model in the code ESRAY&ESPIC
J. Zhang, S. Illy, I. Gr. Pagonakis, J. Jelonnek and M. Thumm
Institute for Pulsed Power and Microwave Technology (IHM),
Karlsruhe Institute of Technology (KIT), Germany
In Magnetron Injection Guns (MIGs), secondary electrons are generated by the bombardment of
back reflected electrons on the cathode surface. These additional electrons from the cathode surface
have higher probability to be trapped again by the magnetic mirror and the accumulation of trapped
electrons can cause Low Frequency Oscillation (LFO) and damage in the gyrotron.
A new secondary electron emission model based on the Furman secondary electron emission model
[1] was developed for the code ESRAY&ESPIC. The Monte Carlo code CASINO [2] is used in order
to have more accurate angular distribution information of the elastic and re-diffused electrons. The
relation between the incident angle θ0 and the outward secondary electron angle θ and φ is shown in
Fig. 1.
(a) θ distribution
(b) φ distribution
Fig.1 Angular distribution of the secondary electrons under different incident angle.
The secondary emission parameters for the two traditional cathode material tungsten and
molybdenum are deduced by fitting the existing experimental data [3].
The initial gun calculation results show that the secondary electrons will cause the accumulation of
trapped electrons, which could lead to LFO is observed in the gun region.
Acknowledgement:
This work, partially supported by the European Communities under the contract of Association
between EURATOM and KIT, was carried out within the framework of the European Fusion
Development Agreement. The views and opinions expressed herein do not necessarily reflect those of
the European Commission.
The authors are thankful to China Scholarship Council (CSC) for the financial support of this research
project.
References:
[1] M. Furman and M. Pivi, “Probabilistic model for the simulation of secondary electron emission,”
Physical Review Special Topics - Accelerators and Beams, vol. 5, p. 124404, Dec. 2002.
[2] H. Demers, N. Poirier-Demers, N. de Jonge, and D. Drouin, “Three-dimensional electron
microscopy simulation with the casino monte carlo software,” Microscopy and Microanalysis,
vol. 17, pp. 612–613, 7 2011.
[3] D. C. Joy, “A database on electron-solid interactions,” Scanning, vol. 17, no. 5, pp. 270–275,
1995.
Development and Optimization of an Inverse Magnetron Injection Gun
for Future Fusion Gyrotrons
S. Ruess1,2, K. A. Avramidis1, G. Gantenbein1, S. Illy1, J. Jelonnek1,2, I. Gr. Pagonakis1, T. Rzesnicki1
Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany
1
IHM, 2IHE
ABSTRACT
Electron Cyclotron resonance heating and current drive (ECRH&CD) is one of the major
plasma heating and stabilization techniques for nuclear fusion devices. The only source
which is capable to produce the high power microwaves for the ECRH&CD is the
gyrotron. It offers excellent coupling to the plasma and very good localization of the RF
power. The KIT is involved in three major projects: Wendelstein 7-X at IPP Greifswald,
ITER at Cadarache, France and future European DEMOnstration power plant (DEMO).
In order to minimize the necessary number of gyrotrons for future fusion power plants,
KIT is working on feasibility studies for multi-MW (>1 MW) gyrotrons. Additionally, to
achieve a sufficient current-drive efficiency, the operating frequency for future DEMO
gyrotrons will be above 200 GHz.
In this work an inverse Magnetron Injection Gun (MIG) was developed. A new type of
inverse electron gun preferable for the coaxial-cavity gyrotron, but also appropriate for
standard hollow-cavity gyrotrons is proposed. The geometry of the gun allows the design
of a significant larger emitter ring, hence significant larger current densities, using the
same size of bore hole for the super-conducting magnet (SCM) as for today’s gyrotrons.
Additionally, the geometry of the new type is significantly simpler when comparing to
the “conventional” gun. Trapped electrons in the gun region can be prevented much
easier in the design than before. In addition, this new type of gun could be used as a
triode gun without any geometrical modifications.
Acknowledgement
This work is supported by the European Community under the contract of Association
between EURATOM and Karlsruhe Institute of Technology (KIT). It is carried out
within the framework of the European Fusion Development Agreement (EFDA). The
views expressed in this publication do not necessarily reflect the views of F4E or the
European Commission.
INITIAL STEPS TOWARDS MULTI-STAGE COLLECTORS FOR GYROTRONS
Chuanren Wu, K. A. Avramidis1, G. Gantenbein1, S. Illy1, J. Jelonnek1,2,
I. Gr. Pagonakis1, M. Thumm1,2
Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, D-76131 Karlsruhe, Germany
1
Institute for Pulsed Power and Microwave Technology (IHM)
2
Institute of High Frequency Techniques and Electronics (IHE)
ABSTRACT
High-power gyrotrons are the unique sources for electron cyclotron resonance heating and current
drive (ECRH & CD) in plasma fusion devices. Gyrotrons for fusion experiments at the stellarator W7X and the tokamak ITER will operate at frequencies between 100 GHz and 200 GHz. The maximum
RF output power is up to 1 MW/2 MW at pulse lengths ranging from several seconds up to 1 h for
ITER. Today, the electronic efficiencies are typically <35 %. Therefore, always the concept of a
single-stage depressed collector (SDC) is used to recuperate some of the electron beam energy which
is not converted into RF power. Depending on the applied depression voltage, that results in
achievable total gyrotron efficiencies of up to 50 %. Of course, that is sufficient for present plasma
fusion experiments. But, future fusion power plants, such as the demonstration tokamak DEMO will
require significantly better efficiencies (>60 %) to achieve a sufficient fusion gain factor.
One possibility to improve the total efficiency of a gyrotron is to use the so-called multi-stage
depressed collector (MSDC) technology. That technology is well known from TWT or klystron
operation. Those collectors use several intermediate steps of the depression voltage along the electron
beam axis. According to the author’s best knowledge, in case of gyrotron operation there are two
theoretical concepts of MSDC technology known: the one is making use of the non-adiabatic
trajectories of electrons in a strong magnetic field; the other is using a specific E x B drift of the
electrons [1]. Even though that several considerations about theoretical MSDC designs for gyrotrons
exist in the literature [2, 3, 4], there is not any successful implementation of that technology known
for gyrotron operation.
In frame of EUROfusion at KIT the technology of MSDC shall be pushed significantly forward.
Initial steps towards new concepts for MSDC have been done already in 2014. For example, the
theoretical optimal efficiency depending on the distribution of the electron energy has been calculated
and some conceptual simulations have been made. In this presentation, the results of analytical studies
and the latest state of the research will be presented.
Acknowledgement
This work is supported by the European Community under the contract of Association between
EURATOM and Karlsruhe Institute of Technology (KIT). It is carried out within the framework of
the European Fusion Development Agreement (EFDA). The views expressed in this publication do
not necessarily reflect the views of F4E or the European Commission
References
[1] Pagonakis, I.G., et. al., IEEE Trans Plasma Sci., vol. 36, no 2, pp. 469-480, Apr 2008
[2] Singh, et. al., IEEE Trans. Plasma Sci., vol. 27, no. 2, pp. 490-502, Apr 1999
[3] Ives, R. L., et. al., IEEE Trans. Plasma Sci., vol. 27, no.2, pp. 503-511, Apr. 1999
[4] Ling, G., et. al., IEEE Trans. Plasma Sci., vol. 28, no. 3, pp. 606-613, Jun. 2000.
Combined experimental and theoretical study of constriction threshold of large-gap AMF vacuum
arcs
N. Wenzel1, A. Lawall2, U. Schümann2, and S. Wethekam3
1
Siemens AG, Corporate Technology, Günther-Scharowsky-Straße 1, 91058 Erlangen, Germany
2
Siemens AG, Infrastructure & Cities, Low & Medium Voltage Division, Rohrdamm 88, 13629 Berlin,
Germany
3
Siemens AG, Energy Sector, Power Transmission Division, Nonnendammallee 104, 13629 Berlin, Germany
ABSTRACT
In this work, we investigate the constriction threshold of axial magnetic field (AMF) stabilized vacuum
arcs between copper-chromium (CuCr) contacts at gap lengths of about 40 m m. The experiments are
performed in a synthetic test circuit with short circuit currents (50 Hz) of up to about 40 kA (rms). In the
experimental setup, the spatial AMF distribution is varied by means of external Helmholtz coils which
are installed coaxially with a pair AMF-type contacts. The AMF magnetic flux density in the contact gap
is determined by 3D finite element computation. The resulting arc evolution is studied in a demountable
vacuum chamber with a high-speed, high-resolution CCD video camera. The experimental data is
compared to 3D transient simulations of the vacuum arc based on a two-temperature magnetohydrodynamic model of the arc plasma derived from first principles without adjustable parameters. The
plasma simulation delivers streamlines of plasma flow and current density, distributions of plasma
density and temperatures, and the energy impact on t he anode. Experiment and simulation show good
agreement concerning the minimum AMF amplitude needed to obtain a diffuse vacuum arc to prevent
anode spot formation. The results also provide a qualitative understanding of ring structures of the
energy flux to the anode surface observed for the diffuse state of the arc.
Primary = Vacuum Interrupters
Presentation Style: Oral
Speaker’s Name: Andreas Lawall or Norbert Wenzel
NEW ULTRA FAST EARTHING SWITCH (UFES) DEVICE BASED ON VACUUM
SWITCHING PRINCIPLE
Dietmar Gentsch1
ABB AG, Calor Emag Medium Voltage Products,
Oberhausener Straße 33, 40472 Ratingen, Germany
e-mail: [email protected]
phone: +49 2102 121 685
1
ABSTRACT
In the low- and medium- voltage range the vacuum interruption principle has been well
established since 30 years in series production. Based on this experience a new application
of vacuum technology is being introduced for use in the medium voltage range.
This paper presents the design principle and the performance of the Ultra Fast Earthing
Switch (UFES) based on a vacuum insulation device as conceived by ABB Ltd.
The UFES design consists of two main sections: The vacuum device and the corresponding
drive section to close the vacuum device. The vacuum device is divided into two separate
ultra high vacuum zones to create at the one hand a double gap between both contacts in
oder to enhance the dielectric performance significantly, and on the other hand to obtain
redundant vacuums. The two vacuum zones are separated by applying a closed membrane
between both contacts which can be opened by a ctivating the plug contact side and
breaking through the membrane to close the self-blocking contact system within less than
1.5ms.
The UFES system was developed for medium voltage application up t o 40.5kV and the
short circuit current up to 63kA. Both ratings are tested in accordance to the standard IEC
62271-102 at the KEMA laboratory. Furthermore the short-circuit rating can be extended
in the short-time-current (STC) of up to 3s. The design, test results and the application in
commercial solutions are being presented.
Primary = Vacuum Interrupters
Presentation Style: Oral
Dielectric testing of HV vacuum interrupters during capacitive current switching
B. Baum1, H. Janssen1, V. Hinrichsen1
1
Technische Universität Darmstadt, High Voltage Laboratories, Darmstadt – 64283, Germany
ABSTRACT
Vacuum circuit breakers are well established in the distribution voltage level due to their various
advantages, e.g. frequent switching operations, low life-cycle-costs, excellent thermal arc quenching
capabilities, and nearly maintenance free operation [1]. In order to establish this technology at higher
voltages, the dielectric withstand capability must be increased. E.g. restrikes, while interrupting
capacitive currents, have to be identified and reduced. In this work, a test setup to investigate
commercially available high-voltage vacuum interrupters for test voltages up to 200 kV is presented and
its features are discussed. In particular, the simultaneous measurement and analysis of field emission
currents as well as micro discharges shortly after arc extinction will be presented.
References
[1] P.G. Slade “The vacuum interrupter: theory, design, and application”, CRC Press, 2008
Triggered spark gap with internal trigger delay circuit
Wolfgang Däumer, Peter Bobert, Frank Werner
EPCOS AG, A TDK Group Company
Rohrdamm 88, 13629 Berlin, Germany
O (oral presentation)
C (primary topic): Vacuum Interrupters and Spark gaps
A2 (secondary topic): Pulsed Power Switching
Abstract
Currently used triggered spark gaps for medical applications like lithotripsy and
electric shock wave therapy ESWT are covered with government administration
restrictions for an export control (article 3A228 of EU export control list for dual use
electronic components). The export control is valid for switching components with
peak currents >= 500A and breakdown delay time <= 15 µs. Triggered spark gaps
fall under the export control because of their short delay times caused by the very
fast development of the gas discharge avalanche. However for the applications in
medical treatment these short breakdown delay times are not important.
A triggered spark gap device with build-in trigger delay circuit and a mechanism,
called locking fuse, which disables the function of the whole component when trying
to remove the delay circuit, is presented. The typical breakdown delay time will be
increased to typical > 25 µs, so that the device is not covered by article 3A228. The
typical operation voltage lies in the range between 8 kV and 20 kV, maximum peak
currents up to 8 kA and long life time with more than 4 million impulses.
The build-in trigger head locking fuse mechanism gives the guarantee, that the
trigger delay circuit cannot be short circuited without destroying the whole trigger
connection to the main gap.
GIANT CURRENT DENSITY IN KOOPS-GRANMAT- IS IT DUE TO A BEC CONDENSATE
AT ROOM TEMPERATURE?
Hans W. P. Koops, HaWilKo GmbH, Ober-Ramstadt Germany
[email protected]
®
Koops Gran Mat surpasses all known materials in carrying giant current densities and
anomalous high currents. The values are much higher than for normal metals ( Au: < 250
KA/cm,²), and in high TC superconductors using Cooper pairs (Bosons) at 70K (Ti-doped
MgB2 < 1 MA/cm² ( 1]), and as high or even higher than Carbon Nanotubes and Graphene
(1 GA/cm²) at 300 K[ 2]. CNT and Graphene have overlapping electron states- which allows
BEC at room temperature- but are limited by phonons influence from the substrate( M.
Fuhrer [ 3]). In field emitter tips emission currents > 3 GA/cm² were experimentally
measured (Pt/C, and Au/C- nanogranular materials produced by FEBIP – Focused Electron
Beam Induced Processing,[ 4] 1994, and [ 5] 2000. The nanocrystals in the material have 2
nm or 4 nm diameter, being embedded into a carbon matrix with Pt-crystals distances of <
1 nm. Crystal diameters ranged from 1.8 to 2.1 nm for the Pt/C material. The metal crystals
are surrounded by s urface electron orbitals states according to Bohr’s atom model with a
perimeter length of 3-, 4-, 5- electron wavelengths of ca. 2 nm. The levels with 5 λ extend
more than half into the carbon matrix and overlap in 3 dimensions to the same levels of the
neighbouring Pt crystals. This forms even at room temperature a network of overlapping
electron states of similar energy throughout the NGM material. The Eigenstates have
energy level distances of 125 meV ( Pt/C) or 65 meV (Au/C) above the Fermi-level[ 6]. The
energy difference corresponds to the measured activation energy for hopping of electrons
into the material. The resistivity of the material has a negative slope with rising
temperature. This is in contradiction to metal or semiconductor materials characteristics.
According to Bose and Einstein, a BEC condensate immediately forms, if overlapping
electron states exist in the material. In superconductors this condensate is occupied from
Bosons: composed from 2 electrons and Bohr Magnetons with anti-parallel spins and have
a diameter up t o 600 nm [ 7]. Like in lasers an infinite number of Bosons can reside in 1
energy level in 1 state, and they are coherent. The possibility of charge transport also for
neutral Bosons built from 1 electron and 1 hole exists. However the electrons and the hole,
which attract each other must have the same spin, which balances the attraction of the two
charges. This results in the same extended Boson diameter (up to 600 nm). Having a field
emitter situation, where a high field is applied (7 10^7 V/cm) electrons can tunnel through
the field into the vacuum. However Bosons, which reach the tip of the NGM tip first need
to decay into electron and hole. The hole goes back into the NGM on the excitonic level to
form a new Boson with any other free electron in this level.
1
P.C. Canfield S. Bud`ko Spectrum d. Wiss. Juni 2005 p. 56
Chandramouli Subramaniam et al. Fig. 1 c, ” Nature Communications Vol.:4, 2202, 23.7.2013
3
M. Fuhrer quotedat page 3247 in “Seong Ki Lee et al in Nano Letters 2012 12 , 3472”
4
J. Kretz et al. Microelectronics Engineering 1994, 23, 477-481.
5
F. Floreani et al. Nuclear Instr. & Methods in Physics Research A 2002, 483, 488-492.
6
, H. W. P Koops et al. J. Vac. Sci. Technol. 1996, B14, 4105.
7
http://www.supraconductivite.fr/en/index.php#supra-explication
[2]
SELF-SCREENING EFFECT OF INDIVIDUAL CNT FIELD EMITTER
WITH HIGH ASPECT RATIO
Wolfram Knapp
Otto-von-Guericke-Universität Magdeburg / IFQ
Universitätsplatz 2, D-39106 Magdeburg, Germany
[email protected]
ABSTRACT
It is a w idely accepted fact, based on num erous experimental studies, that stand-alone CNT field
emitter with high aspect ratio have very good e lectron emission properties, such as low threshold
voltage, high emission current and current density, long-term stability and so on. B ut a surprising
result of some measurements is a “st rong saturation” of electron field emission (FE) at very high
emission current, e.g. IE > 100nA for an individual MWCNT (cf. [1], FIG. 2 and FIG 4), without CNT
field emitter destruction! Because abrupt transitions are atypical for well-known FE limitations (e.g.
space charge limitation, purely ohmic resistance limitation), a self-screening effect was assumed and
investigated.
At first, an elementary model for self-screening effect specifications was developed. Model-based
simulations show, a current dependent emitter voltage drop is the reason for a dramatic changing of
field geometry of the applied macroscopic electrostatic field. And so, without warning, the field
emission characteristic changes transition-free in the self-screening limitation characteristic. In my
contribution I present and discuss following results:
- The reason of self-screening effect is the CNT emitter resistance and a resultant CNT voltage drop
at higher emission current (IE > 100nA for an individual CNT), how shown in [2] and [3].
- The outcome of this self-screening effect is a virtual cathode.
- The virtual cathode has the geometry (3D geometry) of the equipotential surface of the emitter tip
potential (exact: potential of field emission area). In contrast, the real cathode surface (cathode
substrate and CNT emitter surface) is only the equipotential surface of zero field-emission current.
- The enhancement factor is a function of (a) field-emitter geometry and (b) emission current [3].
- Self-screening limitation characteristic is quasi-stationary. It means self-screening limitation is a
dynamic effect between continuous operation field emission switch-off and switch-on, like a jitter
function.
- Self-screening effect can measure very well on individual CNTs with high aspect ratio, high
emitter resistance and in small vacuum gaps.
References
[1] J.-M. Bonard, K. A. Dean, B. F. Coll, and C. Klinke, “Field Emission of Individual Carbon
Nanotubes in the Scanning Electron Microscope”. Phys. Rev. Letters 89, 19 (2002), p. 197602-1.
[2] E. Minoux et al., “Archieving High-Current Carbon Nanotube Emitters,” Nano Letters 5, 2135 (2005).
[3] L. Hudanski et al., “Carbon Nanotube based photocathodes,” Nanotechnology 19, 105201 (2008).
A fully kinetic and self-consistent simulation of a HEMP -thruster using a statistical
approach for solving the “anomalous electron transport” problem
Günter Kornfeld1
Kornfeld Plasma & Microwave Consulting
The paper provides information about the authors developments on simulations of HEMP-thrusters with
no further assumptions than geometry and magnetic field configuration, the applied anode voltage, the Xe
gas flow and the neutralizer current, all defined in an input file. The major plasma collision processes
should be implemented in the code. The selected baseline code was XOOPIC, an open source 2d3v
plasma simulation code written in C++ and developed by the Plasma Simulation Group around Charles K.
Birdsall and John Verboncoer at the Berkeley University of California. Starting from their internet version
2.70, dated 11-Jul-2012 and the corresponding XGRAFIX version 2.70.2, which enables the use of
comfortable simulation diagnostics, the author implemented in the source code modifications and
additional modules required for meaningful simulations of the HEMP- thruster:








exception treatment for neutral (zero charge) particles in the code to allow for
continuous supply of neutral Xe particles for unlimited time simulations,
correction of the “plasma source” module for proper functioning (used as neutral gas source),
multiple background gases (NGDs) for neutral Xe0 and single charged Xe1+ implemented in the
code and the input file,
addendum of the initial background gas densities (NGDs), which are used up with time, with the
time depending respective local particle densities “rhoSpecies” for Xe0 and Xe1+.
In addition to the single ionization of those gases, leading to Xe1+ and Xe2+ ions, introduction of
one step double ionization collisions producing Xe2+ and Xe3+ ion particles respectively,
introduction of a removal procedure for Xe0 and Xe1+ particles after ionization process,
introduction of elastic collisions between neutral Xe0 particles.
In an input file, the geometry of a fictive HEMP- thruster and its plume region is split in a grid of axial
256 times 128 radial cells. A pronounced geometrical downscaling with a factor  =1e-4 was selected.
According to the scaling laws for the Maxwell equations all scaled particle trajectories remain unchanged
if following applies: Distances d' =  * d, fields E' =  -1 * E and B' =  -1 * B, whereas the potentials,
velocities and currents remain unchanged. Thus for the simulation time step we have dt' = * dt and select
dt' =1e-15 s to observe the Courant condition. To gain on the particle number and simulation time, we
don't scale the currents invariant but start with I' = * I and the initial neutral pressure not like p' = -3 *p
but like p' =  -1 *p. The latter, physically follows Paschen law p'*d' = p*d, which keeps the collision
probability along a certain particle trajectory constant. With these scalings, the selected grid cell
dimensions are in the order of the Debeye length.
Remaining problems due to insufficient electron cross field transport required additional code work. They
were found to result from an incorrect over-interpretation of colliding electron coordinates in the standard
Monte Carlo collision modules, as used also in the baseline XOOPIC code. Those codes assume, that the
starting coordinates of primary and created electrons after collision are identical to the coordinates of the
incoming, colliding electron, thus binding the new or scattered electrons again to the same magnetic flux
line in a magnetized plasma. As will be explained, this assumption is not justified within the scope of a
uniform particle density inside the cells and the granularity of the number of particles np2c represented by
a computer particle. In fact the locations of the outgoing electrons are only known to be within the same
grid cell and therefore should be randomly selected within the cell where collision occurs.
It will be shown, that using this approach without artificial assumptions on anomalous electron transport,
allows realistic simulations of a HEMP-thruster at very low currents (10-4 to 3*10-3 from nominal 1.5 A) .
This has not only a physical similarity value for nominal operation but the method seem to allow
investigation of the operational regime at the low edge of the dynamic range of a thruster.
__________

Corresponding author, E-mail: [email protected]
X-Band Hollow-Beam Klystron Design with Corkscrew-Modulation
Jiwei Nie, Heino Henke
Technische Universität Berlin, Sekr. EN-2, Einsteinufer 17, Berlin, 10587, Germany
André Grede
Hüttinger Elektronik, Boetzinger Str. 80, Freiburg, 79111, Germany
Abstract: A hollow-beam klystron with corkscrew
modulation has a series of advantages. Here, a tentative
design of a high efficient klystron at x- band is given. With
three gaps an extraction efficiency of 50% was achieved
for a 100 kV, 10 A beam. The power gain is 49 dB.
Keywords: Traveling wave tube; vacuum electronics;
hollow beam
I. Introduction
The hollow beam corkscrew modulated klystron is based
on an annular beam which is velocity modulated in a ring
cavity operating in a rotating TM m10 -mode. As a result the
beam develops a density modulation in the drift-space of
corkscrew shape. The advantages of an annular beam are
related to the larger beam cross section area and larger
cavities. Here, we give a first design of a klystron with
input cavity, an idler cavity and a three gap output cavity at
10 GHz, Fig.1. Eigenvalue and PIC simulations have been
performed with the code GdfidL[2].
Table 1. OUTPUT POWER AND OUTGOING BEAM
VELOCITY β IN ONE TO THREE GAP CAVITIES
cavity
output power
β
One gap
210 kW
0.35
Two gaps
Three gaps
310 kW
465 kW
0.2
0.13
The bandwidth of the three gap cavity is about 4.6%. Then
the normalized velocity decreases from originally 0.55 to
0.13 after the third gap. All simulations are done with a
single cell modulating cavity.
The input cavity has a loaded Q of about 285. A modulation
factor of 0.45% has been achieved with 7 W input power.
An idler cavity was added to increase the modulation and
thus the gain. It has the same geometry as the input cavity
but is tuned 1MHz higher than the input cavity, such that
the voltage has 70° phase shift ahead of the current. The
Q-factor is 6300. The idler increases the beam modulation
to 5.1%. and the bunching of the beam. The possible power
coupling between cavities were suppressed by radial choke
lines close to the cavities, Fig. 1. The distances between the
cavities are determined to assure maximum efficiency. A
full PIC has been done and 500 kW RF power could be
extracted from the beam. The power gain is 49 dB. In- and
output cavity are connected to a four transmission line
network.
A preliminary design of a hollow beam gun is also given. It
turns out that compression is not necessary.
Figure 1. Schematic drawing of the klystron. In- and output
cavities with four coupling lines and idler cavity (all in red),
beam pipe (green) and three chokes (golden)
II. Design with TM110-Mode Cavities
In a first step the three gap output cavity was designed. The
beam has a current of 10 A and a voltage of 100 kV, i. e. a
normalized velocity of β=0.55. The modulation degree of
the beam is 5%. For cavities with more than one gap we
need π-phase shift between cavities and a good coupling.
So four magnetic coupling slots were chosen at the high
magnetic field position near the outer conductor in the
cavity. The extraction efficiency is seen in Table I.
III. Design with TM310-Mode Cavities
Alternatively, cavities operating in a TM310-mode were
considered. In that way the current could be increased to
50A. Also, the output cavity is modified to four gaps and
electric instead of magnetic coupling. The extraction
efficiency is now 50.2%.
References
1. A. Grede, H. Henke, Concepts for circular deflection
modulated tubes and frequency multiplying millimeter
wave sources, IEEE Intern. Conf. IVEC 2009, Rome, pp
552 – 553
2. Warner Bruns, http://www.gdfidl.de/
Broadband Traveling Wave Tubes in Ka- grants modern communication
E. Bosch, A. Laurent, P.Ehret, Jean Gastaud
THALES Electron Devices, 78141 Vélizy (France) and D-89077 Ulm (Germany)
Email: [email protected], [email protected], [email protected];
[email protected]
Abstract: The paper presents the capability of THALES
Traveling Wave Tubes (TWT) for broadband satellite
applications in Ka-band.
In the last years on the communication market a significant
increase of data transfer has been recognized. The
frequency needs shift step by step from C-band to Ku-band
and now is using the full Ka-Band. Based on this
continuing trend the satellite infrastructure has to provide
a flexible and broadband solution for the communication
equipment. The RF amplifier has a key role in the definition
of the performance. The Traveling Wave Tube technology
is able to support the broadband characteristic. THALES
provides a portfolio of TWTs which will cover the need of
the payload manufacturers. THALES has an outstanding
experience in developing and manufacturing Traveling
Wave Tubes and can demonstrate an impressive in orbit
heritage. This tremendous experience was baseline for a
full portfolio in Ka-Band from lower power up to 170 W
and 250 W under development.
Keywords: Traveling Wave Tube; TWT; broadband; Kaband, high power Ka-band TWTs
Introduction
The trend on the communication market is requiring
continuously more and more data. New applications are
being installed and the amount of information exchange is
increasing day by day. This demands signals in high quality
and high channel capacities. As the end user is increasingly
dependent to have access to the data at any time and
everywhere, high reliability of the data transfer is also very
important. For satellite applications the system architecture
has to use broadband equipment. Also the trend towards
higher output power and higher frequency has to be
realized. For decades THALES Traveling Wave Tubes
demonstrate beside the high reliability in orbit that this
technology can effectively be adapted to the demand of the
payload performance requirements. In the running
THALES production program and development programs
in Ka-band for higher power increased bandwidth the
results show an nice efficiency improvement. In spite of
necessary modifications of the design mainly due to
increased output power the heritage is always respected.
The THALES portfolio will be completed with broadband
designs covering the total Ka-Band and the new designs
will cover up to 2.9 GHz bandwidth in the output power
classes up to 250 W. This will give the flexibility to the
customers in channel bandwidth or channel allocation
within the band. Also an optimization for narrowband
application can be done. Radiation cooled versions will be
in the portfolio as well as conduction cooled versions.
TWT broadband needs in Ka-Band
The high data transmission and large through put on the
satellite requires wider Channel bandwidth resulting in
mostly the full available bandwidth in Ka-band ( 2,9 Ghz)
frequency. Beside the increase of the bandwidth the
behavior has to be well balanced and with low linearity
impacts to allow linearizing the signal. The leads to strong
efforts on the TWT design.
TWT broadband performance
In the following the latest results of the THALES
development tubes in Ka-band will be shown. It will be
concentrated on performance over frequency. To be able to
use advantages from a broadband amplifier the most
important parameters are symmetrical and flat behavior vs
frequency of RF output power, DC input power and gain.
In Ka-band first the current 130 W design has been updated
by a new helix taper design. An improvement by +2% total
efficiency has been demonstrated. Qualification status is
given by a heritage to big number delivered and in orbit
operated tubes. The design is introduced into production
since beginning 2014. Shown in the figure is the
performance for 2 GHz bandwidth. The max phase shift at
highest frequency is 53 deg.
As the market demands an increase of the output power
THALES performed an development program to be
prepared to offer 170 W output power over the complete
Ka-band (2.9 GHz bandwidth). In the next figure results of
one development tube is presented.
The maximum phase shift is 55 deg. The radiator size is
185 mm. The radiation cooled version is going to be
offered to the market in 2015. The conduction cooled
version is already available.
The trend of the market for the future to higher output
power will continue. To be prepared THALES has started
development programs for the 250 W class. Both radiation
cooled and conduction cooled designs will be offered. The
qualification for the radiation cooled version will be
finished in 2017 and for conduction cooled in 2016. The
radiator size is defined with 210 mm. First development
tube results are already available. These can be seen in the
next figure. The total phase shift is 55 deg at highest
frequency.
Conclusion:
The paper describes the design improvements achieved in
the full Ka-band power range and will be extended to
higher power in the full paper. The results today are fully in
line with the expectation of broadband requirements and
extent the large portfolio of Thales TWTs from L to VBand with high efficiency and low non linearity’s.
THALES 150 W C-BAND TRAVELLING WAVE TUBES
W. Dürr, C. Dürr, P. Ehret, E. Bosch
Thales Electronic Systems GmbH, Söflinger Strasse 100 - 89077 Ulm - Germany
ABSTRACT
Since recent years a clear trend has emerged on the world market of travelling wave tube
(TWT) to higher output power, increased bandwidth and higher efficiency. With raised output
power the payloads have possible reach the limit with dissipated power and the wish for
radiation cooled C-band tubes will expressed by the payload manufactures. Competitors
have shown in other frequency bands their strength and it can be expected that they will also
introduce a high performance C-band tube with improved efficiency in near future. For this
reason it is very important for Thales to introduce a new generation of radiation cooled TWT.
Design characteristics
The TL4150R is designed to operates at full frequency range of 3.4 - 4.2 GHz for downlink
commercial communications to cover future market needs, provides a typical RF output
power of 150 W CW, providing sufficient margin und specified operating conditions. The
development was focused on the thermal management, the RF characteristic and new
subassemblies components.
The high power gun is designed with higher beam compression and higher output power and
is equipped with a positive ion barrier to protect the cathode and increase life time.
Additional performance for future output power increase will be also secured.
The new line is improved to increase the RF bandwidth up to 800 MHz, to increase tube
efficiency and to avoid oscillation to guarantee stable operation.
Introducing a new innovative 5 stage collector into the C-band TWT family rises the overall
efficiency at 150 W up to 74% on selected channels. Using the tube in wideband mode 71%
efficiency is possible.
The RF input and output are matched to archive a VSWR lower than 1.33:1 (17 dB) between
3.4 – 4.2 GHz. To handle multipaction at lower frequencies the output transition
(TNC-connector) is changed in size and diameter.
Performance Results
The TWT can be operated over the entire
frequency band (800 MHz) with the same
voltages. By adjusting the voltages the RF
performance can be optimized for selected
frequency channels. Typical small signal
gain values are at 60 dB for 150 W output
power. The phase shift at 4.2 GHz is approx.
52°.
75
74
73
72
71
70
69
68
67
3,4
3,6
TL4150 BB4
3,8
4
TL 4115 SN86
4,2
Conculsion
The predevelopment phase was very successful. The C-band TWT performance is
significantly improved, not only a higher output power was achieved, but also an improved
overall efficiency and an improved bandwidth performance. Qualification, additional margin,
reliability tests and life tests are the upcoming task to finalize the product.
Bead-Pull Measurement of a W-Band Folded Waveguide Structure
Heinrich Büssing1, André Grede2, Heino Henke1
1
Technische Universität Berlin, Einsteinufer 17, 10587 Berlin, Germany
Hüttinger Elektrotechnik, Bötzinger Straße 80, 79111 Freiburg, Germany
2
Abstract
The paper presents a simple and cheap bead-pull
measurement technique for W-band traveling wave
structures.
b
d
p
h
Keywords
Field Measurement, Traveling wave tube, vacuum
electronics.
Introduction
Although modern simulation techniques are very
powerful and are the standard procedure for designing
electron tubes, one still has to verify the fabricated
structure by cold measurements. Here a simple and cheap
bead-pull technique for traveling wave tubes is presented.
It determines the electric field along the beam pipe axis
and allows for calculating the interaction impedance by
integration.
Figure 2a. Two halves of a W- Figure 2b. Zoom into the 0.9mm
band folded waveguide structure.
deep serpentines with b=0.3,
h=0.6, p=0.55, d=0.4mm
Figure 2c. 50µm metal bead on a
8µm kevlar fibre. 1mm distance
between markers of the ruler.
Network analyzer
Control Unit
Diode Detectors
Reference
f
-10dB
Terminator
-10dB
6f
Sweeper Multiplier
Directional Couplers
40
20
DUT
Reflection
Electric Field along Beam Pipe Measured at 92 GHz
60
|E| in kV/m
To measure the reflection in magnitude and phase with a
scalar network analyzer, four measurements have to be
done with the reflected signal self interfered at 0, 90°,
180° and 270° by an adjustable short as shown in fig. 1.
0
-80
-70
-60
-50
-40
Distance in mm
-3dB
Adjustable Short
Measurement Method
In this example the perturbation measurement is applied
to a folded waveguide traveling wave tube at w-band (90
… 98GHz) as shown in fig. 2a and b. A 50µm Al bead on
a 8µm kevlar fiber (fig 2c) is pulled by a stepping motor
through the beam pipe (z-direction) and the reflection
parameter s11 is measured in magnitude and phase. The
electric field at position z is calculated in (1), where the
factor k is achieved by both, simulation and measurement.
(1)
The magnitude of the electric field is shown in fig. 4a.
The voltage an electron experiences on it its way along
the beam pipe with a certain velocity ß is
V eff =∫0 e
⋅E dz
This Veff is shown in fig. 4b for different ß.
(2)
6
x 10
Figure 4b. The voltage an
electron experiences on its
way along the beam pipe
computed with (2) for
different velocities ß. The
synchronous velocity is at
ß=0.2445
4
Veff
Figure 1. Simulated vector network analyzer, using directional couplers,
a combiner and an adjustable short to self interfere the reflected signal.
j ω z
βc 0
-10
Synchronous Velocity
6
z max
-20
Figure 4a. Magnitude of electric field at 92GHz along the beam pipe.
Combiner
E ( z)=k⋅√ Δ s 11 (z)=k⋅√ s 11 with bead ( z)− s 11 without bead
-30
2
0
0.15
0.2
0.25
ß
0.3
0.35
References
[1] A. Grede, H. Henke, R. K. Sharma, "RF-structure
design for the w- band folded waveguide TWT
project of CEERI", IEEE Proc. IVEC 2011,
Bangalare, pp. 213-214
[2] Charles W. Steele, “A Nonresonant Perturbation
Theory”, IEEE Transactions on Microwave Theory
and Techniques, Vol. MTT-14, No. 2, February 1996
[3] Warner Bruns, http://www.gdfidl.de/
Simulation of Beam-Wave Interaction in Filter-Type Slow Wave Structures
of Travelling Wave Tubes
Philip Birtel 1, Elke Gehrmann2, Sascha Meyne2, Arne F. Jacob2
Thales Electron Devices, Söflinger Straße 100, 89077 Ulm, Germany
2
Technische Universität Hamburg-Harburg, Institut f. Hochfrequenztechnik, 21073 Hamburg, Germany,
1
ABSTRACT
Accurate numerical simulation tools are a critical requirement for the design of competitive travelling
wave tubes (TWTs). While there are commercial solutions to this task, these are general-purpose tools
that have simulation times of many hours or even days, making them impractical for design work.
Instead, a manufacturer of TWTs, such as Thales Electronic Systems, has to create special-purpose tools
with a very limited range of applicability, but with simulation times several orders smaller. There is an
ongoing DLR-funded cooperation with the TU Hamburg-Harburg to extend and improve the programs
that compute the beam-wave interaction in filter-type slow-wave structures (SWS). An interaction tool
for folded-waveguide SWS (“KLYSTOP”), and an interaction tool and a design method for filter helices
are two recent results of this cooperation.
A folded waveguide SWS consists of regularly spaced
and alternately oriented “teeth” that form the eponymous
waveguide. A hole for the beam is drilled through the
teeth. The folded waveguide has a limited pass band for
propagating waves, which makes it akin to the more
expressively discrete coupled-cavity SWS. However, due
to the large number of teeth (~100) the exchange of
energy between beam and wave is continuous, like that in
a helical SWS. In order to account for that somewhat hybrid nature of the folded waveguide, an accurate
equivalent-circuit model of the SWS was developed, and a suitable convergence method (quasi-Newton)
was employed for the interaction program. Also, considerable work was done on the transition and sever
elements [1]. The accuracy of the thus extended simulation program was demonstrated by comparison to
measurements.
The “filter helix” is a method to selectively suppress the harmonic
of the operating signal, which is created by the nonlinearity of the
beam-wave interaction, in order to increase the efficiency of the
device. It consists of a section of the helical delay line in which the
pitch of the helix periodically and abruptly changes, thus creating a
stop band at the harmonic, while propagation and amplification at
the operating frequency is unimpeded. The effects of the filter are
simulated by assuming both a forward and a backward travelling
wave, which are coupled via reflections occurring at the pitch discontinuities. The filter helix has now
been successfully employed in a 500W S-Band TWT in order to extend its operating band towards lower
frequencies, where the harmonic is especially strong [2].
[1] S. Meyne et. al., in Proceedings of the 15th International Vacuum Electronics Conference, Monterey,
April 2014, IEEE, pp. 15-16.
[2] E. Gehrmann et. al., IEEE Trans. on Electron Devices, Issue 6, Vol. 61 (1014), 1859-1864
HOT MATCHING ANALYSIS OF A GENERIC TWO-SECTION COUPLED-CAVITY
TRAVELING-WAVE TUBE
Sascha Meyne1, Jean-François David2, Arne F. Jacob1
1
Institut für Hochfrequenztechnik, Technische Universität Hamburg-Harburg, Hamburg, Germany
2
Thales Electron Devices, Vélizy, France
ABSTRACT
Coupled-cavity traveling-wave tubes (CC-TWTs) provide large output power with high efficiency at
microwave frequencies. It is important to study the matching condition of CC delay lines with and
without electron beam to understand the implications on the tube performance. Considering the trend
towards higher frequencies, delay lines such as folded waveguides (FWG) are currently investigated.
They can be modelled in a similar fashion as CC delay lines, so the analysis presented here is directly
applicable to FWG-TWTs.
Normally, the cold match of a delay line, i.e., without electron beam, is optimized in order to ensure
stable and efficient operation. However, the matching changes during operation due to the presence of
the modulated electron beam [1]. Thus, an effective characteristic impedance change has to be
considered to predict stability and performance of the tube [2, 3].
In this contribution a generic CC-TWT with two sections is considered (Figure 1). The tube consists of
nine and eleven cavities, respectively, and has couplers at the in- and output as well as severs between
the two sections. An ideal hot match derived from a small-signal interaction model is applied to couplers
and severs at each frequency. The matching condition is thus defined by the characteristic impedance of
the coupled beam-wave system. Therefore the couplers and severs are assumed to exhibit the proper
frequency dispersion. Although this might be a somewhat idealized assumption, several important
practical conclusions can be drawn.
Interaction is simulated with small- and large-signal models. Stability and amplifier gain are analyzed.
The results confirm that the matching condition derived from the small-signal model leads to residual
reflections under large-signal operating conditions. Nonlinear effects which are not included in the
calculation of the matching condition are shown to play a major role in this case and thus determine the
tube performance.
References
[1] S.O. WALLANDER, IEEE Transactions on Electron Devices Vol.19 No.5 (May 1972), pp. 655, 660
[2] S. MEYNE, J.-F. DAVID, and A.F. JACOB, in Proceedings of the German Microwave Conference
(GeMIC), Aachen, Germany, March 2014
[3] S. MEYNE, J.-F. DAVID, and A.F. JACOB, in Proceedings of the IEEE International Vacuum
Electronics Conference, Monterey, CA, April 2014, p. 15.
Figure 1: Generic two-section CC-TWT