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


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


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


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


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


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


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)



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


E-field at 800 MHz Agreement between independent methods


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


E-field at 500 MHz


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


E-field at 500 MHz


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


*Note: vertical in model x direction


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⊗


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


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

4

5

6

7

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

(°)



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



Slotted Kicker - Coaxial, Longitudinal Coupling Z


Real Imaginary


Slotted Kicker - Coaxial, Transverse Coupling Z


Real Imaginary


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

2

4

6

8

10

12

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



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


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


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


Additional Information

Stripline Kicker - Coupling Impedance and Matching


sps wideband transverse kicker evaluation and design

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