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‘Development and Commissioning of a Single Non-linear
Kicker Magnet System for the BESSY II Storage Ring Injection’
O. Dressler, P. Kuske - USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Content
• Non-conventional Injection vs. 4 Kicker Bump
- Improvement Matching of Conventional 4 Kicker Bump
• Undisturbed Injection in Top-Up-Mode
• Non-linear Magnet Development and Laboratory Test
- Concept, Evolution of Design, 2D Magnetic Field Calculations
- Comparison of Different Pulse Circuit Topologies
- Realization of Magnet and Connections with good Symmetry
- Laboratory Tests for Magnetic Field Measurements
• Non-Linear Kicker Commissioning and Design Improvements
- Mitigation of RF Power Losses
- Commissioning of Non-linear Kicker as Storage Ring Injection
- Measured Beam Excitation with Kicker Magnet
• Summary and Outlook
• Extra: Principle of Kicker Circuit, Linear Transducer
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Non-conventional Injection vs. 4 Kicker Bump
Conventional layout of BESSY II Storage Ring Injection
Two similar injection septa and four separately powered injection kickers in one straight section.
Non-conventional injection with one single non-linear kicker
Application of the two injection septa and one single pulsed non-linear kicker magnet outside the
injection straight for special injection procedure in top-up-mode *.
*PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS 10, 123501 (2007),
New injection scheme using a pulsed quadrupole magnet in electron storage rings, Kentaro Harada,
Yukinori Kobayashi, Tsukasa Miyajima, and Shinya Nagahashi, Photon Factory
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Improvement Matching of Conventional 4 Kicker Bump
Exercise: Changing the intrinsic pulser circuit
impedance improves the matching of the four
different current pulse shapes.
Result: Adjustment of circuit inductances
achieves better matching of the injection
kicker pulses than before.
Problem: The adjustment could only be preserved within ±2% in the long term (month). The
inherent timing jitters and drifts of the four single thyratron driven kicker pulsers units cause
transverse beam excitations still, and therefore, reduce injection efficiency.
O. Dressler, J.-O. Kuszynski, ‘Matching Pulse Shapes of the BESSY II Storage Ring Injection Kicker System / High Precision Pulse Measurements’, PPC05, Monterey, CA, U.S.A., 2005
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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Mitigation by Series Connection of two Kicker Magnets
Result:
• The injection became much less sensitive to
timing adjustments and jitters of the two pulsers.
• The sensitivity to trigger timings decreased from
±35ns before to about ±350ns now.
Difference
Mitigation:
Idea:
The matching of the two pulse currents is ±0.5%.
Move septum magnet to the beam axis by 1/3.
Reduce kicker pulse current from 6.8 kA to 4.5 kA.
• Relaxing injection geometry.
• Series connection of two kicker magnets on one
pulser unit each side of septum magnet.
• Maintained only two independent pulse current
shapes and timings equal.
Problem: Applied pulse currents between both pulser units differ by 30% for lowest beam excitation.
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Undisturbed Injection in Top-Up-Mode
Aims: For the ‘Top-Up’ operation mode of the BESSY II storage ring an electron beam current of
300mA must be maintained constant for a long time period. The loss of electrons will be
compensated continuously by a new injection every 30s, ideally without any excitations resulting
in transversal oscillations of the already stored beam. Therefore a pulsed non-linear kicker was
inserted into the accelerator at a suitable position. At this point the injected electron beam is
deflected closer to the already stored electron beam, and so, will be accumulated. The term
‘non-linear’ refers to the characteristic magnetic field distribution of induction By inside the magnet.
Magnetic field distributions:
Dipole
Quadrupole
Sextupole
Octupole
Non-linear
Tasks for single non-linear kicker magnet system development:
Beam optics calculations, magnet system concept, magnetic field calculations, rf estimations,
mechanical design, power electronics, control electronics, integration, etc.
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Non-linear Magnet Concept / Calculation of Induction
Concept: Design one single kicker magnet with non-linear field characteristics, zero Bx,y-field
in the center and an off-axis maximum, By, which is horizontally displaced by 10-12 mm.
Achieve the lowest possible vertical gap height by an in vacuum magnet.
Table of Parameters
Calculation of Induction By
Parameter
Value
Deflection angle
1 mrad
Maximum induction By
25 mT
Magnet bore (hor. x ver.)
42 mm x 10 mm
Active magnet length
280 mm
Length half-sine current pulse
1.5 µs
Primary peak current ÎP
1750 A
Secondary peak currents ÎS
2 x 700 A
K  B0  l [ Tm ] 
 [ rad ]  p [ GeV c ]
0 .3
 [ rad ]  p[ GeV c ]
B0 [ T ] 
0.3  l [ m ]
(1)
(2)
K  Kick stregth
  1mrad Specified deflectition angle
l  0.28m Length of magnet
B0 [ T ] 
0.001[ rad ]  1.72[ GeV c ]
0.3  0.28[ m ]
B0 [ T ]  20 mT
Values of pulse currents are stated for
current design solution, after all iterations.
Two coils of top and bottom magnet halfs
are in series, both are connected in parallel
to the pulser unit.
B0min = 20 mT, induction required at least
By at y = 10 mm
Specifications
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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Non-linear Kicker Magnet, 2D B-Field Calculations
Non-linear refers to the specific characteristics of magnetic
Evolution of Design: 4 conductors, 4 coils,
with ceramics support and vacuum pipe profile. Induction By. This was to be confirmed by measurement.
Desired:
4 currents into one direction
The kicker magnet posses
mirror symmetry on its
horizontal and vertical middle axis.
Direction of scalability of design.
Measures in [cm]
Final design with bore of vacuum pipe
and titanized ceramics support.
POISSON SUPERFISH, Report No. LA-UR-96-1834,
7 Feb. 2007, Los Alamos National Laboratory
Specifications:
By max. ≥ 20 mT, depiction in [G], (1 G = 1•10-4 T)
By max. at y = 0 and x = +10 mm
By min. at y = 0 and x = -10 mm (symmetry condition)
Bx = 0 along y = 0
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Comparison of Different Pulse Circuit Topologies
Traveling Wave Circuit
Characteristic
impedances:
50, 25, 12.5Ω
Pro:
• Pulser unit in save distance to
magnet, therefore no radiation.
exposure of power electronics
• Small attenuation by cable only.
Con:
• Impedance matching required.
• Small impedance mismatch by
load inductance deteriorates
slew rate of pulse current.
• High charging voltage necessary
because of system impedance.
Lumped Element Circuit
Pro:
• High currents on small
load impedance.
• High accuracy possible.
• Low ripple on pulse top.
Con:
• Small distance to magnet.
• Foot width vs. pulse top
of half-sine pulse current.
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Circuit Topologies with and without Transducer
Lumped Element Pulser - Resonant Circuit
Resonant Circuit with Transducer and Cable
Idea: add 1:1 transducer!
Resonant Circuit + Connection Cable
Distance by Insertion of Coaxial Cable Possible?
Difficult for short pulses!
Resonant Circuit with Cable Inductance
Solution: Pulser / Short Cables / Magnet
Transducer 1:1, Number of Windings n = 2
Problem: Pulser generates
high transient voltages to
ground on magnet.
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Realization of Magnet and Connections
2D Magnet Model
Schematics of Electrical Connections
Four Kicker Coils
Symmetry
axis
Sectional View 3D Magnet Model
Options for Coil Interconnections
• 2 coils in parallel on 1 transducer
(top/bottom), 2 circuits in parallel.
• 2 top and 2 bottom coils in series using
1 transducer respectively (installed).
• 4 coils in series on 1 transducer (future).
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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Photo of Non-linear Kicker Inner Structure
Ceramic support
Coils
Flange
Water cooling pipe
Flange
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Laboratory stand
Olaf Dreßler
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Set-up for Magnetic Field Measurements
Procedure for Magnetic Field Measurements:
• Measurement of in long straight coil induced
voltage v(t) at succeding horizontal positions.
• Instantaneous calculation of magnetic flux φ(t)
out of voltage trace with the storage oscilloscope.
• Readout of max. value Фmax from oscilloscope
for actual position, division by known coil area.
• Plot points into digramm.
 ( t )    v ( t )dt
B0 max 
 max
A
Typical scope picture of B-field measurement
Voltage signal in
pick-up coil [V]
Magnetic flux [Φ]
Direction of vertical
B-field measurement,
Magnet rotated by 90°
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Pulse current [V~A]
Olaf Dreßler
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Magnetic Field Measurement vs. ANSYS Calculation
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Conventional vs. Non-linear Kicker Injection
Local Orbit Bump Injection
Neighboring kicker magnets (K1 + K2 and
K3 + K4) are powered in pairs to form a local
pulsed orbit bump for beam accumulation.
Non-linear Kicker Magnet Injection
One pulsed non-linear kicker magnet located
outside the injection straight at an effective phase
advance of 45° in reference to the injection point.
Turn-by-turn measurement of horizontal and vertical beam oscillations due to kicker schemes.
• 4-kicker injection bump optimized
for small orbit perturbation.
• Injection efficiency ~ 80%
• rms orbit perturbation
horizontal ~ 1.000mm
vertical
~ 0.500mm
• Standard injection, beam current 300mA
• Significant perturbation of the stored beam
in both planes, horizontal and vertical
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
• Single non-linear kicker injection,
not yet completely optimized.
• Injection efficiency ~ 80%
• rms orbit perturbation
horizontal ~ 0.060mm
vertical
~ 0.015mm
• Injection up to a beam current of 300mA
possible
• Second design was cured from rf warming
Olaf Dreßler
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Commissioning of Non-linear Kicker magnet (1)
Methodology of Measurements:
The kicker magnet was excited by its nominal current (4 x 700A). The kicker timing relative to
the storage ring injection was changed stepwise [µs]. The kick strength [kick/µrad] into either
horizontal or vertical direction, measured at a particular horizontal / vertical geometric position
(x / y [mm]) of the beam in the vacuum pipe, is shown in the plots.
Set-up:
All 4 magnet coils were powered in parallel, on 2 transducers for upper and lower magnet half
respectively (previous schematic). Maximal efforts for tuning of current symmetry had been done.
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Commissioning of Non-linear Kicker magnet (2)
Set-up:
The 2 magnet coils magnet coils of top and bottom magnet half were connected in series, on
2 transducers for upper and lower magnet half respectively, and tuned for best current, and
hence, magnetic field symmetry.
Result:
• In both coil set-ups a minimum of beam excitation in horizontal direction can be detected.
• While in the first case as minimum for vertical beam perturbations is far away from the
horizontal minimum, in the second case one finds much better agreement with the theory.
• Supposition that only a series connection of all four kicker coils will achieve horizontal and
vertical minima at the same x / y position.
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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Acknowledgement
We would like to acknowledge the determined and
very successful collaboration of the HZB project team:
• Scientific project leader: P. Kuske
• Power electronics and magnet concept: O. Dressler
• Mechanics and magnet design: M. Dirsat
• Magnetic field calculations: T. Atkinson
• RF design: H. Rast (TU Dortmund)
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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Summary
• Integration of magnet system; timing, control & power electronics are effectively working.
• Successful tests of non-linear kicker magnet in BESSY II storage ring for beam injection
is achieved. Beam injection and accumulation were easily attained.
• RF warming of 1st structure was reduced by design changes for 2nd magnet structure
by a complete coating of ceramic support surfaces with sufficient titanium thickness.
• Upper and lower half-coils are currently powered in series to achieve better By-field
symmetry, and at the same time, reduce necessary over all pulse current, and hence,
the applied voltage on the structure.
• Usage of one single pulse power supply in a lumped element circuit has the advantage
that current amplitude and amplitude stability are no issue for the functionality
as injection kicker system.
• First studies of beam excitation and injection efficiency show satisfying results.
Further studies in top-up mode are ongoing.
• The series connection of all coils is feasible and may reduce the measured imbalance.
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
Olaf Dreßler
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Outlook
• Development efforts are proposed for a 3rd magnet prototype to remove remaining
design bugs, to achieve better reliability of the kicker magnet in long term operations.
• Eddy currents in mechanical support structure near the connections outside the vacuum
system cause imbalance of upper and lower half pulse currents.
Therefore, adjustment and synchronism of pulse currents in upper and lower kicker
magnet half on one pulse power supply must be improved by inductance tuning.
• The deployment on two synchronized lumped element pulser units for top and bottom half
of magnet is feasible. Here timing jitters and pulse current synchronism must be obeyed
to avoid excitations of stored beam.
• The application of one traveling wave kicker system to power the magnet from a
distant, radiation protected place by one solid state pulser unit could be studied.
• How does the change of dynamic apertures by insertion devices in different operation
conditions influence the injection efficiency?
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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Symmetry by Positioning of Coils and Connections
Series connection of two coils in upper magnet half
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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Schematics of Linear Transducer
Conzept: Pulser / Transducer / Magnet
Schematics of Linear Transducer
Transformation ratio 1:1, only
prim. + sec. stray inductance add on
M  K L1  L2
Transducer in saturation
CT2
(1)
M - Mutual inductance,
K - coupling ratio
Scope picture
as example for
non-linearity
and saturation
of core material
CT1
Properties:
• Primary and secondary stray inductance of
windings and connections
• Non-complete coupling
• Eddy current and hysteresis losses in core
material, possible saturation
• Transformation ratio ≠ 1:1 causes
transformation (increase) of load impedances
and hence longer current pulses
t
1
dI
dI
I1dt  RI1  LS  L1  1  M 2  0

C0
dt
dt
LM  L2  dI2  M dI1  0
dt
dt
LE
d 2I1
dI
1
 R 1  I1  0
dt
dt C
LE  LS  LM

L1 1  1  K 2  / 

1   
L2


(2)
(3)
(3) in (2)
LE - Apparent inductance
of pulser circuit, in (4)
LL
L2
(4)
(5)
β in (5)
(6)
α in (6)
(7)
* Heinz Knoepfel, S. 143, Physical effects and generation methods concerning pulsed fields
up to the megaoersted level, Verlag: North-Holland Publ. Co. (1970), ISBN-10: 0-444-10035-0
USR Workshop, Huairou, Beijing, Oct. 30 - Nov. 1, 2012
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