SPS Wideband Transverse Kicker Evaluation and Design
Transcript of SPS Wideband Transverse Kicker Evaluation and Design
SPS Wideband Transverse Kicker Evaluation andDesign
Progress and Plans
J. M. Cesaratto1
Kicker Design Contributors:
J. M. Cesaratto1, J. D. Fox1
S. DeSantis2, Z. Paret2, H. Qian2, A. Ratti2
W. Hofle3
D. Alesini4, A. Drago4, S. Gallo4, F. Marcellini4, M. Zobov4
1Accelerator Research Department, SLAC National Accelerator Laboratory2Lawrence Berkeley National Laboratory
3BE-RF Group, CERN4INFN-LNF
LARP/HiLumi Collaboration Meeting CM20, April 17, 2013
J. M. Cesaratto LARP CM20 April 17, 2013 1 / 22
Outline
1 Introduction, the need for a wide band kicker, design evaluationcriteria
2 Kicker designs, possible implementations, simulation resultsCavityStriplineSlotted, 3 flavors
3 Summary
J. M. Cesaratto LARP CM20 April 17, 2013 2 / 22
Introduction
Purpose: Need for a Wide Band Kicker
The current SPS tapered stripline rolls off at 200 MHz, kicker of largerbandwidth necessary is for intra-bunch dynamics control.
For the application of controlling electron cloud (ecloud) and transversemode coupling instability (TMCI)
Establish a baseline for implementation of a vertical kicker system in thesuper proton synchrotron (SPS)
Review, evaluate, and determine the capabilities of several possibleimplementations with the criteria:
1 Shunt impedance2 Beam coupling broadband
impedance3 Bandwidth4 Heating issues
5 Fabrication complexity &complications
6 Vacuum chamber compatibility7 Ease of coupling to external
amplifiers
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Introduction
Progress in 2012 – 2013
Evaluation of three structures for use as wide band transversekickers in the SPS, cavities, striplines, slotted structures
Refinement on specification of the SPS beam stay-clear andaperture requirements
Revised stripline design compatible with beam stay-clear
Extensive modeling of the slotted slow wave structure, investigatedthree variations
Established collaboration between SLAC – LBNL – CERN – LNF,interest by LNF to build a prototype kicker for installation intoSPS
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Kicker Designs Cavity
Cavity kicker
Use several narrow band cavities tokick at high frequencies
Used in conjunction with a striplinefor the low frequencies
Several processing channelsnecessary
Phasing between multiple kickersnecessary
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Kicker Designs Stripline
Stripline Kicker
Redesigned to comply with SPS beam stay-clear requirements
Derived from ALS camshaft kicker (which is 3 times smaller)
Modeled in CST MS
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10 cm in length
Kicker Designs Stripline
Stripline Kicker - Transverse Shunt Impedance
2 wire method in MS to determine
R⊥T2 (breaks down at DC)
1 kΩ at 500 MHz,400 Ω at 750 MHz
Larger dimensions increase straycapacitances and lower HOM cutoff,disrupting shunt impedance athigher frequencies.
As it is now, kicker could likely beused in the DC – 500 MHz range.
In order to reach to 1 GHz, needs tobe used with high frequencystructure
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Power estimate at 750 MHz → Pmax = 25 kW!
Kicker Designs Slotted
Slotted Kicker
Similar structures to those used in stochastic cooling at Fermilaband CERN
McGinnis type – WaveguideFaltin type – Coaxial
Investigated three variations of slotted kickers
WaveguideRidged waveguideCoaxial
Quarter geometries shown (and on next slides)
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Kicker Designs Slotted
Slotted Kicker - Fermilab’s model
500 600 700 800 900 1000 1100 12000
10
20
30
40
50
60
Frequency (MHz)
Tra
nsv
erse
Shunt
Imped
ance
(kΩ
)
HFSS
Moment Method
Waveguide and beam pipe couple together by slots
Initial simulations carried out by moment method calculation,Slotted Pickups
Simulations verified with HFSS
A more flexible tool, more quantitative outputDifferent geometries simulated easily
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E-field at 800 MHz Agreement between independent methods
Kicker Designs Slotted
Slotted Kicker - Ridged Waveguide
200 400 600 800 1000 12000
5
10
15
20
25
Frequency (MHz)
Tra
nsv
erse
Shunt
Imped
ance
(kΩ
)
With HFSS, explore variations of the slotted structure
Including a ridge in the waveguide increases the bandwidth, andlowers the operating frequency.
The shunt impedance is reduced, but still at very acceptable levels
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E-field at 500 MHz
Kicker Designs Slotted
Slotted Kicker - Coaxial, Shunt Impedance
0 200 400 600 800 1000 12000
2
4
6
8
10
12
14
Frequency (MHz)
R⊥T
2 (
kΩ
)
Slot length 125 mm
Slot length 80 mm
Including a coaxial line in the waveguide increases the bandwidth of theslotted structure
Shunt impedance is markedly reduced, but still at very acceptable levels
Voltage phase response linear at low frequency, see next slide
Very promising candidate
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E-field at 500 MHz
Kicker Designs Slotted
Shunt Impedance Comparison of 3 structures
0 200 400 600 800 1000 12000
10
20
30
40
50
60
Frequency (MHz)
R⊥T
2 (
kΩ
)
Waveguide
Ridge
Coaxial SL 125 mm
Coaxial SL 80 mm
0 200 400 600 800 1000 1200−100
−80
−60
−40
−20
0
20
40
60
80
100
Frequency (MHz)
φV
t (°)
R⊥T2 =
V 2⊥
2Pin V⊥ =
∫ L
0(Ex − cBy)e
iωzc dz
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*Note: vertical in model x direction
Kicker Designs Slotted
Initial Coaxial Type Parameters
6
?h in = 5 mm
?
6
wh = 50 mm
6
?
bh = 52.3 mm
6
?thick = 1 mm
-
w in/2 = 40 mm
-sl/2 = 40 mm
-ww/2 = 75 mm
-bw/2 = 75 mm⊗
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In z-direction (⊗, beam axis into page):
- slotted length, al = 1000 mm
- slot width, sw = 5 mm
- slot spacing, ss = 20 mm
*Note: sl/2 is shown to be 40 mm,but initially was 72.5 mm
*Note: vertical direction is x
Kicker Designs Slotted
Optimizing Slot Width - Spacing
All parameters of the structure werevaried with the goal of maximizingshunt impedance and bandwidth
As an example, slot width andspacing periodicity
Slot width and spacing in thez-direction, direction of the beam.
40 slots, over 1 m
Initially started with 5 mm width,20 mm spacing, aspect ration 1:4
The aspect ratio which maximizedthe shunt impedance is ∼ 1:1
Phase of transverse voltage nearlylinear up to 600 MHz → importantfor feedback function
0 200 400 600 800 1000 12001
2
3
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8
9
10
11
Frequency (MHz)
Tra
nsve
rse
Sh
un
t Im
pe
da
nce
(kΩ
)
2.5 mm
5 mm
7.5 mm
10 mm
12.5 mm
15 mm
17.5 mm
20 mm
22.5 mm
0 200 400 600 800 1000 1200−100
−80
−60
−40
−20
0
20
40
60
80
100
Frequency (MHz)
Ph
ase
(°)
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Kicker Designs Slotted
Increasing/Decreasing the Number of Slots
More kick strength can beachieved by increasing theperiodicity of slots - length ofslotted section fixed at 1 m
Beam coupling impedanceincreases as well
Coupling impedancecalculations on going withGdFidL as design evolves (seeslides 16 and 17).
Discussions with CERN ABPgroup necessary to specify SPSimpedance budget for thisstructure
0 200 400 600 800 1000 12002000
3000
4000
5000
6000
7000
8000
9000
10000
11000
Frequency (MHz)
Tra
ns S
hunt Im
pedance (Ω
)
20 slots
40 slots
80 slots
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Kicker Designs Slotted
Slotted Kicker - Coaxial, Longitudinal Coupling Z
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Real Imaginary
Kicker Designs Slotted
Slotted Kicker - Coaxial, Transverse Coupling Z
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Real Imaginary
Kicker Designs Slotted
Transverse Uniformity
How does the shunt impedancevary off the axis of the beam?
Presented for two slot length(horizontal direction) cases:
1 125 mm2 80 mm
Transverse displacementmodeled up to 20 mm off axis
1 Shunt impedance reduced by18%
2 Shunt impedance reduced by39%
Discussions with CERN ABPgroup necessary to properlydetermine the necessaryuniformity.
0 200 400 600 800 1000 12000
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14
Frequency (MHz)
Tra
nsve
rse
Sh
un
t Im
pe
da
nce
(kΩ
)
0 mm
5 mm
10 mm
15 mm
20 mm
0 200 400 600 800 1000 12002
3
4
5
6
7
8
9
10
Frequency (MHz)
Tra
nsve
rse
Sh
un
t Im
pe
da
nce
(kΩ
)
0 mm
5 mm
10 mm
15 mm
20 mm
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Kicker Designs Slotted
Optimize Coax to Stripline Interface
Matching input port power powerto stripline
Optimize the stripline,waveguide, and coaxialdimensions to achieve propermatching consistent withparameters necessary tomaximize shunt impedance andtransfers kick uniformity.Simulations on going, may bedifficult to achieve minimalreflection over entire frequencyband.
Example, varying the coaxialwidth, w in.
0 200 400 600 800 1000 12000
0.2
0.4
0.6
0.8
1
Frequency (MHz)
|S11|
10 mm
20 mm
30 mm
40 mm
50 mm
60 mm
70 mm
80 mm
90 mm
100 mm
?
Input port
)1w in
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Summary
Summary
Three structures have been explored as possible kicker options for theSPS wide band feedback effort
Options:
A stripline operating from DC - 400 MHz, with two or three cavitiesA stripline with a slotted kickerArray of striplinesA slotted coaxial kicker
Ideally, would like one structure to cover the entire band. The coaxialtype slotted kicker is an attractive option
Slotted kicker simulations on going to fine tune dimensions for matchingthe structure
Design report being written now, compiling all results and analysis fromevaluation study, to be submitted to CERN
LNF interested in building a vacuum compatible prototype of the kicker,detailed mechanical drawings necessary
Acknowledge essential collaboration between the four laboratories
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Additional Information
Stripline Kicker - Transverse Uniformity
Isolines of Ey at steady state
Each line separated by 2%
Wider electrodes, to ensure highfield uniformity, cause overalldimensions to be larger in order tomaintain 50 Ω characteristicimpedance
Note, in model vertical is y direction
Ey vs. x at y = 0 Ey vs. y at x = 0
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