1. CLIC DR Extraction Kicker and Future Testing at ATF
M. Barnes
CERN TE/ABT
Acknowledgements:
J. Holma (CERN), C. Belver, A. Faus-Golfe (IFIC), F. Toral (CIEMAT)
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

2. Overview of presentation
Specifications for kickers for CLIC Damping Ring (DR) Extraction Kickers;
Overview of design of Pulse Generator (Inductive Adder) and Striplines for CLIC DR;
Fast kicker R&D at ATF;
Modifications required to CLIC DR kicker to allow use in ATF;
Decisions required before prototyping of kicker ….
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

3. CLIC General Layout
TA kicker
Loop phase compensation kicker
Phase measurement
Dump
kicker
DR Extraction Kicker
244 kickers for Drive Beam. For Main Beam = Turn-Around Kickers
CR injection is by an RF deflector (NOT kickers).
Dump kickers are NOT foreseen.
CR only 3 passes, but impedance is an issue because of very high beam current.
Turn around impedance is probably an issue -> Drive Beam passes through 24 TA kickers!
Emergency kickers in drive beam => Similar requirements to CR & TA kickers.
Compact Linear Collider (CLIC) study aims at a center-of-mass energy range for electron-positron collisions of 0.5 to 5 TeV, optimised for a nominal center-of-mass energy of 3 TeV (3 TeV CLIC). In order to reach this energy in a realistic and cost efficient scenario, the accelerating gradient has to be very high - CLIC aims at an acceleration of 100 MV/m. Superconducting technology being fundamentally limited to lower gradients, only room temperature travelling wave structures at high frequency (12 GHz) are likely to achieve this gradient. In order to optimize the production of sufficient RF power for this high gradient, and CLIC relies upon a two-beam-acceleration concept: The 12 GHz RF power is generated by a high current electron beam (drive beam) running parallel to the main beam. This drive beam is decelerated in special power extraction structures (PETS) and the generated RF power is transferred to the main beam. This leads to a very simple tunnel layout without any active RF components (i.e. klystrons). Both beams can be generated in a central injector complex and are transported along the linac.
A total of approximately 300 kickers will be required for CLIC ! ;
Damping Rings: one injection and extraction system per ring and per beam (8 kicker systems);
Damping rings reduce beam emittance; hence kickers must be high stability (low ripple and droop) with excellent integrated field homogeneity and very low beam coupling impedance.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

4. DR Kickers: Selected CLIC, ILC & DAΦNE Parameters
CLIC Pre Damping Ring
CLIC Damping Ring
ATF
ILC
DAΦNE
Beam energy (GeV)
2.86
1.3 5
0.51
Total kick deflection angle (mrad)
2.0
1.5 3
0.7
Aperture (mm)
~40 20 11
24 (tapered)
54.8 (tapered)
Effective length (m)
2*1.7
1.7
2*0.6
20*0.32=~6.4
0.94
Field rise time (ns)
700
1000 ~5
Field fall time (ns)
Pulse flattop duration (ns)
~160 NA
Input pulse duration (ns) ~6
5.9
5.3
Flattop reproducibility
±1x10-4
1x10-3
Flattop stability [inc. droop], (Inj.)
per Kicker SYSTEM (Ext.)
±2x10-2
±2x10-3
±2x10-4
1x10-4
Field inhomogeneity (%) [CLIC: 3.5mm radius]
[CLIC: 1mm radius]
±0.1 (Inj.)
±0.1 (Ext.)
±0.01(Ext.)
±?? ±3
±10
Repetition rate (Hz) 50
3M burst
5 (3M burst)
Pulse voltage per Stripline (kV)
±17
±12.5
±10 ±5
±45
Stripline pulse current [50 Ω load] (A)
±340
±250
±200
±100
±900
Longitudinal beam coupling impedance (Ω)
< 0.05*n
Transverse beam coupling impedance (kΩ/m)
< 200
Takashi NAITO showed an estimated (measured) stability, of the kick angle, of 2x10^-3, see “Fast kicker performance in ATF”, Low Emittance Rings Workshop (LER2010), January 12–15, 2010, CERN.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

5. Schematic of CLIC DR Kicker System with an Inductive Adder
DR Kicker with an Inductive Adder
Schematic of CLIC DR Kicker System with an Inductive Adder
Beam upstream end of striplines
An extensive literature review of existing pulse generators has been carried out: an inductive adder is a very promising means of achieving the demanding specifications for the DR extraction kickers.
Two of the main challenges of DR kickers
Impedance matching of ALL parts/components over a wide frequency range (… striplines are particularly challenging);
Stability of ALL parts/components (with time, temperature, ….).
Inductive Adder of 14 Layers
½ Layer of an Inductive Adder
MOSFETor IGBTs
Capacitor
Gate Driver
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

6. Predictions for Various Modulation Schemes
PSpice simulations of the effect of the value of the capacitance per layer upon the flattop droop, with:
no modulation,
active analogue modulation (am);
passive analogue modulation (pm).
20µF
40µF
20µF - pm
320µF
40µF - pm
160ns
20µF - am
Without modulation 320 µF, per layer, is required to achieve 0.02% droop over 160 ns.
An analogue modulating layer is very effective at controlling droop, even with a relatively small value of the capacitor banks;
Critical design issues include:
low inductance for capacitor bank circuit,
small parasitic capacitances,
impedance matching (e.g. of pulse transformer) to minimize reflections
temperature stability of magnetic characteristics of transformer cores and careful choice of material;
For tape-would transformer cores, adequate interlaminar insulation;
etc..
For a prototype inductive
adder it is proposed to use
~80 µF, per layer.
Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

7. Beam-Line Kicker Element
The specifications for the pre-damping rings and the damping rings include:
low longitudinal and transverse beam coupling impedances;
high stability and reproducibility of the field;
excellent field homogeneity;
ultra-high vacuum.
Feedthru
Ceramic Support
Taken from: D. Alseni, LNF-INFN, “Fast RF Kicker Design”, April 23-25, 2008.
Beam
Elliptical cross-section (increases deflection efficiency).
DAΦNE Striplines (~0.9m)
Stripline structures will be used for the beam-line kicker element;
IFIC, in conjunction with CIEMAT & CERN, are carrying out a complete optimization of the design of the DR striplines;
Spanish Industry (TRINOS) will produce manufacturing drawings and a set of prototype DR striplines;
The striplines will be supplied with suitable high voltage vacuum feedthroughs (Stripline feedthroughs will probably be supplied by Kyocera: 15KV-F-Coaxial UHV).
Note: each taper ≈ 30% of overall length.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

8. Stripline Optimization: ”Flat” Electrodesh
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

9. Beam Impedance: V2 (Optimization for Even Mode Impedance = 50Ω)
Aperture = 20 mm
Electrode thickness = 4mm
Electrode edge length = 5 mm
Electrode edge angle = 45°
R = 20 mm → h/R = 0,68
(Z0)e = 49,5 Ω
(Z0)o = 40,7 Ω (FH)o = 0,16%
R = 25 mm → h/R = 1
(Z0)e = 50,2 Ω
(Z0)o = 36,8 Ω (FH)o = 0,01%
R = 30 mm → h/R = 1,18
(Z0)e = 50,9 Ω
(Z0)o = 33,7 Ω
(FH)o = 0,005%
Where (see previous slide).:
h is electrode height (without taking into account the electrode edges);
R the inner kicker radius.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

10. 13th ATF2 project meeting. January 13, 2012
Fast Kicker R&D at ATF
Demonstration of a Beam Extraction (2009~)
Swap the conventional pulse kicker with the fast kicker but only in this R&D period
Slide adapted from: N. Terunuma, KEK. LER11, Heraklion, Crete, Greece, Oct. 2011
1.3 GeV electrons are circulating at 2.17MHz (460ns length) in the ATF DR.
Pulser performance study (2005~2009)
It has been done here by measuring the beam oscillation.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012 10

11. 13th ATF2 project meeting. January 13, 2012
Beam Extraction Orbit using Strip-line Kicker, Aux. septum & Pulse bump
Courtesy: N. Terunuma, KEK. LER11, Heraklion, Crete, Greece, Oct. 2011
Stored beam
Local Bump
Extracted beam
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

12. 13th ATF2 project meeting. January 13, 2012
ATF Striplines
Kicker pulse
(10kV) [FID Co. Ltd]
Kicker field
2~1.3m overall length
Courtesy: N. Terunuma, KEK. LER11, Heraklion, Crete, Greece, Oct. 2011
Rise time
1.5 ns
Rise time
5 ns
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

13. CLIC DR Kicker & Variations for ATF
CLIC Damping Ring – spec.
CLIC DR v2a for ATF (Z0E=50Ω)
[1.3m, ±12.5kV]
CLIC DR v2 for ATF
(Z0E=50Ω)
[1.3m, ±15kV]
CLIC DR v1a for ATF
(Z0O=50Ω)
CLIC DR v3 for ATF
ATF
Beam energy (GeV)
2.86
1.3
Total kick deflection angle (mrad)
1.5
2.5
3.0
5.0
3.0 or 5.0 ?
Aperture (mm) 20 12
Effective length (m)
1.7
2*0.6 or 0.45?
Field rise time (ns)
1000
~250
~100 ~5
Field fall time (ns)
Pulse flattop duration (ns)
~160 NA
Input pulse duration (ns) ~6
Flattop reproducibility
±1x10-4
1x10-3
Flattop stability [inc. droop], (Inj.)
per Kicker SYSTEM (Ext.)
±2x10-3
±2x10-4
Field inhomogeneity (%) [CLIC: 3.5mm radius]
[CLIC: 1mm radius]
±0.1 (Inj.)
±0.01(Ext.)
±??
Repetition rate (Hz) 50
3M burst
Pulse voltage per Stripline (kV)
±12.5
±15
±10
Stripline pulse current [50 Ω load] (A)
±250
±300
±200
Longitudinal beam coupling impedance (Ω)
< 0.05*n
Higher than v2
Transverse beam coupling impedance (kΩ/m)
< 200
Estimated additional cost (kCHF) 75
Takashi NAITO showed an estimated (measured) stability, of the kick angle, of 2x10^-3, see “Fast kicker performance in ATF”, Low Emittance Rings Workshop (LER2010), January 12–15, 2010, CERN.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

14. 13th ATF2 project meeting. January 13, 2012
Timeline
Inductive Adder:
samples of main components ordered, to start testing in first-quarter of 2012;
a prototype layer scheduled to be ready for testing in the third-quarter of 2012;
order all components for a prototype stack by end of 2012 (select voltage: ±12.5kV or ±15kV);
build and test prototype stack by mid-2013;
order components, build and test a second IA stack;
Striplines:
optimization of stripline design , for even-mode characteristic impedance and field homogeneity, is underway;
re-optimize stripline design , for odd-mode characteristic impedance and field homogeneity (for reduced field rise-time in ATF)???
longitudinal and transverse beam coupling impedance, with tapers, to be calculated (together with Wakefields);
complete stripline electromagnetic design by June 2012 (select stripline length: 1.7m or 1.3m, and “odd or even” mode of 50Ω characteristic impedance), and give design to TRINOS Vacuum Projects for mechanical design and prototyping;
Possibly use different cable types (i.e. different losses) to “balance” losses, e.g. for a double kicker system losses in paths of different lengths could be similar to relevant frequency components…..
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

15. 13th ATF2 project meeting. January 13, 2012
Summary
The CLIC DR extraction kickers are presently being designed, since they are particularly challenging ,as they require:
low longitudinal and transverse beam coupling impedances;
good integrated field homogeneity;
excellent stability (±0.02 %* requirement for the pulse flattop stability);
Two [±12.5kV] inductive adders & [1.7m] tapered striplines are required for the CLIC DR, with Z0E=50Ω, and the plan was to prototype these.
* To be compared with T. Naito’s extensive experience with double kickers and striplines.
It would be very interesting to test the inductive adders and striplines in the ATF. This would not only confirm the design of these elements but would provide ATF with a high stability kicker system with good integrated field uniformity. But the CLIC DR parameters are NOT compatible with ATF:
are the modified kicker system parameters (±15kV and a 1.3m version of prototype striplines with Z0O≈50Ω  ~100ns field rise and fall time, 20mm/12mm aperture 3mrad/5mrad) acceptable for ATF?
would you consider putting this modified kicker system in ATF?: if so, it could be a “test” kicker or a replacement of the double kicker (depends on stability)?
what ATF manpower would be required for installation etc.?
a “recommendation” for/against testing the modified kicker system is required by March 2012, to allow for design modification before manufacturing of the striplines commences (CERN would need to find the additional budget to finance the required modifications to the inductive adders).
Possibly use different cable types (i.e. different losses) to “balance” losses, e.g. for a double kicker system losses in paths of different lengths could be similar to relevant frequency components…..
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

16. 13th ATF2 project meeting. January 13, 2012
Thank you for your attention. QUESTIONS, COMMENTS AND SUGGESTIONS
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

17. 13th ATF2 project meeting. January 13, 2012
RESERVE SLIDES
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

18. CLIC Damping Ring Pulse Definition
Rise time: time needed to reach the required flattop voltage (but includes settling time). DR extraction 1000 ns rise time allowed, <250 ns desired;
Settling time: time needed to damp oscillations to within specification;
Beam: 160 ns time window during which any ripple and droop (i.e. flattop stability) must be within specification;
Flattop stability: within ±2x10-4, for combined ripple and droop for DR extraction. This corresponds to a maximum, combined, ripple and droop of ±2.5 V for a 12.5 kV output pulse for the DR extraction kicker;
Reproducibility: maximum difference allowed between any two pulses, of ±1x10-4;
Fall time: time for voltage to return to zero. DR ext.  1000 ns allowed, <250 ns desired.
Minimizing rise and fall times reduces stress on kicker system.
To minimize settling time, impedance of system has to be well matched.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

19. Principle of IA Modulation Layers
PROBLEM: During output current pulse charge is removed from capacitor banks, hence capacitor bank voltage reduces, causing droop of output pulse.
ANALOGUE MODULATION: layer is used to compensate voltage droop of capacitors, and can also significantly reduce the required capacitance per layer.
No energy storage capacitor on modulation layer, but there is a resistor Ra in parallel with the transformer core (magnetizing inductance Lm);
Resistor Ra is effectively in series with the load;
PASSIVE MODULATION: during the pulse, current through Lm increases, hence current through Ra decreases (τ=Lm/Ra). Therefore, voltage over Ra decreases, compensating voltage droop caused by storage capacitor voltage droop of other layers.
ACTIVE MODULATION: a linear switch provides a shunt path for the current through resistor Ra. Therefore, the voltage over Ra can be controlled by controlling the current through the switch.
DIGITAL MODULATION: switching “On” and “Off” provides coarse modulation and hence will not be used for droop compensation. However turn-on of layers at different times may be used to reduce ripple.
No capacitor here
Linear
switch ic
Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

20. 13th ATF2 project meeting. January 13, 2012
Status of the IA Design
Specifications have been defined for the main IA components, based on existing applications, discussions with Ed Cook, and simulations;
Simulations on-going:
Compensation of droop and ripple using analogue modulation;
Samples of main components ordered:
Storage capacitors, MOSFETs (switch-type and linear devices) and transformer cores;
Components will be tested starting first-quarter of 2012 and the most suitable candidates will be chosen for the prototype;
The first prototype layers are scheduled to be ready for lab testing in the third-quarter of 2012;
Build and test a prototype stack by mid-2013.
Sample components: transformer cores, capacitors, MOSFETs and their gate driver circuits.
Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

21. Measurement Challenges
The ±0.02 % requirement for the pulse flattop stability, for the DR extraction kicker, is an extremely demanding specification from both the design and measurement perspective.
Commercially available Current Transformers (CT) are promising for the measurement device, e.g.:
Short coaxial cables, terminated in their characteristic impedance, to minimize attenuation, dispersion and reflections.
But commercially available oscilloscopes are not capable of measuring shape of pulse flattop to required (relative) accuracy, e.g. because of ~1% amplifier droop over 200 ns.
High speed, 14-bit, Analogue to Digital converter to be investigated…
Pulse measurement experts contacted (e.g. Technical Research Institute of Sweden and ETH Zürich) and discussions commenced.
To confirm effect of analogue modulation by lab measurements (e.g. for droop compensation), two systems, with output currents in opposite sense though a CT (~zero total field without modulation), will probably be required.
Ipeak > 250 A;
Droop over 160 ns < 0.002%;
Rise time < 10 ns, hence measurement ripple introduced by CT is expected to be insignificant after 100 ns target rise-time. Se
+I or −I
Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona) I
M.J. Barnes
13th ATF2 project meeting. January 13, 2012 21

22. Double Kicker System: Concept (Extraction)
Extraction with one kicker magnet:
Requires a uniform and stable magnetic field pulse.
Two “identical” pulses are required;
One power supply sends the pulses to 2 “identical” kickers.
Extraction with two kicker magnets:
1st kicker system for beam extraction;
2nd kicker system for compensation of jitter of deflection angle (ripple & droop) from 1st kicker;
Figure shows 1st and 2nd kickers separated by a betatron phase of 2nπ: for a betatron phase of (2n−1)π the 2nd kick is in the other direction.
(Kicker)
(Anti-Kicker)
Time of flight
Septum after 1st kicker not shown, but would be there (see next slide).
KEK/ATF achieved a factor of 3.3 reduction in kick jitter angle, with respect to a single kicker, with single-bunch measurements.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

23. Example of Double Kicker System for DR Extraction
1st kicker system (in damping ring) for beam extraction;
2nd kicker system (in extraction line) for jitter compensation.
Beam Time-of-Flight compensation.
In order that beam bunches and kicker field are synchronized in time at the 2nd kicker system, the two kicker systems are powered in parallel. However, additional lengths of transmission line are required to compensate for the beam-of-flight between the 1st and the 2nd kickers.
Potential problems
Different attenuation & dispersion of stripline waveforms (due to length of transmission lines);
Differences between magnetic characteristics of kicker & anti-kicker;
Imperfections in beam-line elements/alignment between kicker & anti-kicker.
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

24. Stripline Design: Longitudinal Impedance
Longitudinal beam coupling impedance for untapered (Chao) and tapered stripline kicker (S. Smith, SLAC):
Without dielectric or magnetic materials:
Virtual Ground
+ve
-ve
Beam pipe Ground
Striplines driven to same magnitude, but opposite polarity, voltage, to extract beam
 ODD mode characteristic impedance.
Total capacitance (C) is given by:
capacitance between a stripline and virtual ground (C11)
capacitance between a stripline and beam-pipe ground (2C12)
+/-ve
Beam
Same polarity and magnitude of current / voltage induced on both striplines by beam.
 EVEN mode characteristic impedance
Capacitance (C) is given by:
capacitance between a stripline and beam-pipe ground (C11)
C11
C11
2C12
2C12
C11
C11
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

25. Beam Impedance: V1 (Optimization for Odd Mode Impedance = 50Ω)
BEAM IMPEDANCE: defines the interaction of the beam with the kicker, resulting in beam energy lost and a beam shape perturbation. L l l
Longitudinal beam coupling impedance for untapered (Chao) and tapered stripline kicker (S. Smith, SLAC):
How can we decrease the longitudinal beam impedance?
Optimizing the kicker geometry in order to achieve 50 Ω even mode characteristic impedance,
Acknowledgements: C. Zannini and G. Rumolo
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

26. Stripline Design: Field Homogeneity (V1)
7 mm
20 mm
STRIPLINE
CLIC DR specifications: Field inhomogeneity:
±0.1 % (1e-3) for DR injection (over 3.5 mm radius);
±0.01 % (1e-4) for DR extraction (over 1 mm radius).
2 mm
Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)
Contour plots of field inhomogeneity in the kicker aperture for the optimized design
Sensitivity of field homogeneity to parameter variations from the optimized design (Courtesy of C. Belver-Aguilar)
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

27. Estimated Resources for Inductive Adder V2a
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

28. Estimated Resources for Striplines
J. Holma
LCWS 2011, September 26-30, 2011

29. 13th ATF2 project meeting. January 13, 2012
Other Issues
If only one of the two striplines is powered, beam will receive ~1/2 deflection; high intensity beam could cause considerable damage to other equipment. This could result if a “single” switch were used for each stripline: an inductive adder (multiple primary switches) will help to avoid this problem.
Fast rise and fall times of field are desirable; e.g. if beam is mis-timed, with respect to the kick pulse, a fast rise/fall time will result in beam being swept faster across downstream materials/devices, minimizing potential damage. Se
Testing: ATF or synchrotron light source (e.g. ALBA, Bareclona)
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

30. Tail Clipper: Deflection
From CTF3 CR
To CLEX
Beam (e-)
Strip-line at positive voltage
Strip-line at negative voltage Fe
Deflection due to Electric Field:
From CTF3 CR
To CLEX
Beam (e-) I Fm B
Deflection due to Magnetic Field:
Strip-lines fed from CLEX end +V -V
M.J. Barnes
13th ATF2 project meeting. January 13, 2012

31. ATF Kicker: Measured Electrical Pulses
(FID Co. Ltd)
Courtesy: N. Terunuma, KEK. LER11, Heraklion, Crete, Greece, Oct. 2011
M.J. Barnes
13th ATF2 project meeting. January 13, 2012