Download Development of High Power CW and Pulsed RF Test Facility based

Development of High Power CW and Pulsed RF Test Facility based on 1 MW,
352.2 MHz Klystron Amplifier
M. K. Badapanda*, Akhilesh Tripathi*, Rinki Upadhyay, J. N. Rao, Ashish Tiwari, Akhilesh Jain,
M. R. Lad and P. R. Hannurkar
RF Systems Division, Raja Ramanna Centre for Advanced Technology, Indore, M.P- 452013, India
Abstract
A high power 1 MW, 352.2 MHz RF Test facility
having CW and Pulse capability is being developed at
Raja Ramanna Centre for Advanced Technology
(RRCAT), Indore for performance evaluation of various
RF components, accelerating structures and related
subsystems. Thales make 1 MW, 352.2 MHz klystron
amplifier (TH 2089) will be employed in this high power
test facility, which is thoroughly tested for its
performance parameters at rated operating conditions.
Auxiliary power supplies like filament, electromagnet,
ion pump and mod anode power supply as well as 200 W
solid state driver amplifier necessary for this high power
test facility have been developed. A high voltage floating
platform is created for floating filament and mod anode
power supplies. Interconnection of various power
supplies and other subsystems of this test facility are
being carried out. A high voltage 100 kV, 25 Amp DC
crowbar less power supply and low conductivity water
(LCW) plant required for this klystron amplifier are in
advanced stage of development. NI make cRIO 9081 real
time (RT) controller based control and interlock system
has been developed to realize proper sequence of
operation of various power supplies and to monitor the
status of crucial parameters in this test facility. This RF
test facility will provide confidence for development of
RF System of future accelerators like SNS and ADSS.
INTRODUCTION
A 1 MW, 352.2 MHz, RF test stand based on Thales
make TH 2089 klystron amplifier is being developed at
RRCAT, Indore for characterization and qualification of
RF components, cavities and related subsystems.
Complete 1 MW RF system is shown in Figure 1.
A klystron amplifier is a sensitive device and its life
depends on how stored energies are taken care of, during
internal flashover, arcing, etc., since its arc resistances
reduce to very low value during arcing. Some klystron
manufacturers keep restriction on allowable fusing action
of the arc current, i.e, a limit on the maximum I 2t, while
others keep restriction on the maximum allowable energy
that can be allowed to pass through these arcing klystrons
[1]. The TH 2089 klystron amplifier employed in this
system, can tolerate about 20 Joules of energies called
‘critical energy under arcing’ and about 40 A2Sec of
fusing action called ‘critical fusing action under arcing’
beyond which irreparable damage may occur. A crowbar
_______________________________________________________________
*Primary Authors E-mail:
M. K. Badapanda: [email protected]
Akhilesh Tripathi: [email protected]
Figure 1: Block diagram of 1 MW RF system
less solid state modular 100 kV, 25 Amp DC power
supply is developed and is used as the bias power supply
of this klystron amplifier. The stored energy in this power
supply is less than 20 Joule, which is not detrimental to
this klystron amplifier during its arcing. The 100 kV DC
power supply has the inherent pulse capability which can
be utilized to operate this test stand in pulsed mode also.
The control system is designed and developed for
controlling the sequence of operation of various power
supplies employed for the proper operation of this high
power klystron amplifier. It also controls and monitors
cooling water temperature, pressure and flow, oil
temperature, cooling air flow and other environment
conditions.
HIGH POWER TESTING OF TH 2089
KLYSTRON AMPLIFIER
TH 2089 klystron amplifier is tested for its
performance evolution under rated operating conditions.
Various tests like measurement of RF gain, measurement
of variation of RF phase over beam voltage and beam
current, measurement of output power variation against
beam voltage and beam current and output power
variation against mod anode voltage have been
performed. These tests are carried out at central operating
frequency of 352.2 MHz.
Variation of RF gain with RF input power
This test is conducted for determining the gain
characteristics of this klystron amplifier. The variation of
output power and RF gain against the input power is
shown in Figure 2 and Figure 3 respectively. It is clear
that RF output power initially increases, goes into
saturation and then beyond saturation, it decreases with
increasing input power.
Figure 2: Output power Vs input power
Figure 4: Output power Vs cathode voltage
Figure 3: RF Gain Vs input power
Hence it can be concluded that overdriving a klystron
reduces its output power. The value of the gain decreases
with increase in input power. Klystron is usually operated
near the point of saturation for maximum RF output even
though its gain value reduces at saturation. From Figure
2 and Figure 3 it is clear that saturated output power is
1055.6 kW and gain at the saturation is 41.2 dB.
Variation of RF output power with beam
voltage and beam current
This test is carried out to show how output power
varies with beam voltage and beam current. In this test,
RF output power is plotted against the variation in beam
voltage with rated beam current of value 18.2 A. It is
shown in Figure 4. Value of output power decreases with
the decrease in cathode voltage and become negligible
below certain value of cathode voltage. This is because
below certain cathode voltage, electrons hardly get
accelerated towards collector and hence very less output
power is received. Above certain value of cathode
voltage, internal arcing between cathode and nearby
anode may occur, leading to catastrophic failure of
klystron tube. Hence the graph is drawn only in and
around the rated cathode operating voltage. Again
variation of RF output power against varying beam
current is shown in Figure 5, at constant beam voltage of
92.8 kV. Output power increases with increase in cathode
current and the rate of increment is higher at higher value
of cathode current. The higher is the cathode current,
more is the numbers of electron that reaches from cathode
to collector for same cathode voltage and hence higher is
the output power.
Figure 5: Output power Vs cathode current
POWER SUPPLIES OF TH 2089
KLYSTRON AMPLIFIER
1 MW, 352.2 MHz klystron amplifier requires various
power supplies, such as high voltage beam power supply
(-100 kV, 20 A, DC), modulating anode power supply
(100 kV, 12 mA, DC), filament power supply (20 V, 25
A, DC), ion pump power supplies (5 kV, 10 mA, DC in
two numbers) and electromagnet power supplies (300 V,
12 A, DC in two numbers) [2]. These power supplies are
operated in a particular sequence for proper operation of
TH 2089 klystron amplifier.
High Voltage Platform
Out of several power supplies employed for TH 2089
klystron amplifier, filament and mod anode power
supplies are floating at cathode potential of -100 kV
voltages hence to power the input of these power supplies
an isolation transformer of suitable isolation is employed.
This transformer is tested up to isolation voltage of 150
kV. A high voltage platform is prepared to mount
filament and mod anode power supplies above this
isolation transformer. This transformer has two separate
secondary windings for applying the input to these power
supplies. The control of these power supplies will be
carried out through optical fibre and optical fibre cards
are also mounted over this high voltage platform.
Interconnection of Various Power Supplies with
TH 2089 Klystron Amplifier
The interconnection of these power supplies with TH
2089 klystron amplifier is shown in Figure 6.
Figure 6: Interconnection of different power supplies with TH 2089 klystron amplifier
Beam power supply is basically a solid state modular 100 kV, 20 Amp DC bias power supply with 24 pulsed
input system. It consists of 96 numbers of switched power
modules connected in series and suitably staggered to
minimize the output ripple, hence reducing the
requirement of output filter capacitor and thereby
avoiding the use of crowbar for protecting klystron
amplifier in case of arcing. An inverter bridge based
voltage controlled 100 kV, 12 mA DC power supply is
utilized as modulating anode power supply for this
klystron amplifier. The Modulating anode is positive with
respect to cathode and is floating at cathode potential of
-100 kV. The maximum amplitude of the mod anode
power supply should be such that the potential difference
between the body and mod-anode is never less than 5 kV,
in order to avoid the excessive interception of the electron
beam by the drift tube. A current regulated 20 V, 25 A,
DC power supply is developed as the filament power
supply for this klystron amplifier [3]. Soft start feature is
incorporated in this supply to limit the surge current and
to increase the output current slowly. The cold condition
filament resistance is 0.1 ohm and in hot condition it is
0.85 ohm [4]. So if full filament voltage is applied in cold
condition, very large filament current will flow during
start that may damage the klystron. Hence filament power
supply is started in soft start mode. Two numbers of high
frequency inverter bridge based voltage regulated 5 kV,
10 mA, DC ion pump power supplies are utilised for
creation of necessary vacuum level inside the klystron
tube. For proper focusing of the electron beam in the
klystron amplifier, two numbers of high frequency
inverter bridge based current regulated 300 V, 12 A DC
electromagnet power supplies are employed. A 200 W
solid state driver amplifier has also been developed to
provide the necessary input drive to this klystron
amplifier.
SEQUENCE CONTROL SYSTEM
The sequence control system of 1MW, 352.2 MHz,
CW klystron has been developed in order to drive TH
2089 klystron amplifier. The system is able to control the
operation of several power supplies in proper sequence.
The hardware of sequence control and the interlock
system are based on the NI cRIO 9081(Integrated
1.06GHz dual core controller). The basic function of the
software is to check and indicate the status of various
interlocks as well as for real time data logging. The
software will acquire system parameters like status of
various power supplies, RF status, various channel status
and selection, interlocking system and other incoming
status signal. It process acquired data and control the
system to achieve user defined goals.
CONCLUSION
The high power RF test stand with CW and pulsed
capability is a national facility, which is in advanced stage
of development at RRCAT, Indore for the evaluation and
qualification of advanced accelerator sub-systems. Pulse
capability in this test stand is provided by operating the 100 kV, 25 A bias power supply of TH 2089 klystron
amplifier in pulsed mode. Various factory tests, carried
out for the performance verification of 1 MW, 352.2
MHz, TH 2089 klystron amplifier are presented in this
paper. Interconnection scheme of several power supplies
with TH 2089 klystron and their control system with
suitable interlocks have been developed.
REFERENCES
[1] Badapanda M.K., Hannurkar P.R. and Upadhyay R.,
“Crowbar protection for CW klystron amplifier” Journal of the
Institution of Engineers (India) 91, 3-7, 2010.
[2] M. K. Badapanda, Akhilesh Tripathi, Rinki Upadhyay,
Pundlik R. Hannurkar, "Development of 352.2 MHz high power
RF test setup," ivec, pp.485-486, 2011 IEEE International
Vacuum Electronics Conference, 2011.
[3] Akhilesh Tripathi, M. K. Badapanda and P. R. Hannurkar
“Design and Development of DSP Controlled Filament Power
Supply for 1 MW, 352.2 MHz Klystron”, International Journal
of Engineering Research (ISSN: 2319-6890), Volume No.2,
Issue No.2, pp: 137-140, April 2013.
[4] “TH 2089 Manufacturers data sheet,” Thomson Tubes
Electroniques, France.