Squashed Superconducting Deflecting Cavity for APS at ANL · 2013. 7. 28. · Jiaru Shi Defl. Cav. Workshop, SSRF, Apr.23-25, 2008 2/ 18 Deflecting RF Cavity R&D • Collaboration

Deflecting/Crabbing Cavity Workshop, SSRF, Shanghai

Squashed Superconducting Deflecting Cavity for APS at ANL

Jiaru ShiTsinghua University

Apr 24, 2008

Defl. Cav. Workshop, SSRF, Apr.23-25, 2008Jiaru Shi

2 / 18Deflecting RF Cavity R&D

• Collaboration with ANL, LBNL and JLab– Possible upgrade of the ALS at LBNL

• Single or multi-cell structure in storage ring• Polarization, LOM and HOM damping studies• Prototype cavity at Tsinghua University

– Compressing X-ray pulse at the APS, ANL• Similar requirement as for the ALS• Squashed SC single cell cavity (2.8 GHz)• Prototype (Nb, Cu) at JLab

– Emittance exchange experiment at ANL• 1.3 GHz NC cavity

– Beam diagnostic at Tsinghua • Photo-injector for Thomson Scattering X-ray source • (2.856 GHz NC cavity)

– ILC, LHC study


3 / 18Acknowledgements

• Collaborators– Argonne National Laboratory

• A. Nassiri, G. Waldschmidt• W. Gai

– Thomas Jefferson National Accelerator Facility• R. Rimmer, H. Wang and …

– Lawrence Berkeley National Laboratory• D. Li, J. Byrd, J. Corlett and …

– Tsinghua University, Beijing• H. Chen, C. Tang

• Acknowledgements– KEK

• K. Hosoyama


4 / 18Outlines

• Introduction• Squashed v.s. cylindrical symmetric

– Degenerate modes– Peak magnetic field– Mode damping

• LOM Damper design of deflecting cavity– Simulation using Time domain and Eigen-mode solver– Waveguide on beam pipe

• Resonance coupling between waveguide and cell• Copper model experiment

– On-cell damping• Multi-cell study

– Cell-Cell coupling of dipole mode• Double chain model

– Two cell structure, more cells


5 / 18Compressing X-ray Pulse


6 / 18Accelerating versus Dipole Cavity

For the same resonant frequency at π- mode: - accelerating cavity (TM010) - deflecting/crabbing cavity (TM110 + TE111): both modes

contribute to the transverse kick

Accelerating cavityAccelerating cavity Deflecting cavityDeflecting cavity

Accelerating cavityAccelerating cavity

Deflecting cavityDeflecting cavity

Scaling of physical dimensionsScaling of physical dimensionsField distribution, maximum Field distribution, maximum

Magnetic field at different regionsMagnetic field at different regions


7 / 18SC Deflecting Cavities

• Crab-wise crossing in Colliders– KEK-B cavity– LHC and ILC worldwide

• BNL, SLAC, FNAL, Cockcroft• Short X-ray Pulse Generation

– ALS at LBNL– APS at ANL– SSRF in China

• Other– Kaon separation at Fermi– Emmitance exchange

• NC cavities

KEKKEK--B cavity B cavity


8 / 18Summary of the Deflecting Cavity Study at LBNL

• X-Ray pulse compression using the deflecting cavity for LUX– Studied 9-cell, 7-cell and 5-cell cavities at 1.3 and 3.9-GHz– 7-cell cavity at 3.9-GHz to produce 8.5MV deflecting was proposed

• ALS option– 3-Cell, 2-Cell cylindrical symmetric cavity at 1.5 GHz– LOM and HOM damping was studied.– Al prototype mode w/o and w/ damping waveguide was tested and got very good

agreement with experiment


9 / 18SC Squashed Cavity for APS1

Frequency (GHz) 2.815

Deflecting Voltage 4 MV * 2

Operation CW

Beam Current (mA) 100

• Definitions– deflecting/crabbing cavity (TM110 +

TE111): both modes contribute to the transverse kick

– Panofsky-Wenzel Theorem

– Shunt impedance

APS requirement

Transverse E-field

[1] A. Nassiri


10 / 18Building 3-D Model

• Race-track shape at center plane• Tangent arc-line-arc cross section

– Same equator-radii and iris-radii every section

– Different angle of the straight segment

• Loft in CAD code– Loft rotation from section to section,

iris as guide line– Loft from iris to iris with guide line:

better for adding beam pipe in Microwave Studio


11 / 18Comparing the Geometry

• Constant– Curve radii– Beam-pipe dimension– Cavity length

• Comparing– Peak magnetic field – (R/Q)*– LOM/HOM


12 / 18

Symm. Sqsh. Symm. w/ WG

Sqshw/ WG

Working Mode

(TM110, y)!E

f MHz 2801.5 2800 2795 2795(R/Q)* Ohm 43.06 37.15 48.18 41.95Ep / V 1/m 65.27 69.4 61.89 63.39Bp / V mT / MV 193.49 150.5 212.08 168.5

LOM(TM010)

!E

f MHz 2018.8 2375 2005.7 2376(R/Q) Ohm 103.83 76.7 81.6 75.7Qext 1103 1050

!Tf MHz 2009.6 2368

Qext 777.6 1012

Degenerate Mode

(X-TM110)

!E

f MHz 3667 2798.8 3649(R/Q)* Ohm 12 47.77 14.3Qext 459.2 849

!Tf MHz 2788.9 3635

Qext 453.5 1186

• (R/Q)* -10%• Bp / Vdef -20%• Higer LOM frequency

– Easier to propagate– LOM damping wg

• Degenerate mode– frequency seperation– lower (R/Q)– higher frequency

Symmetric v.s. Squashed


13 / 18How Squashed?

R/Q

Bmax and R/Q v.s. squashed ratio

Rarc D ratio f (R/Q)* B/V E/V f_TM010 f_xTM110

[mm] [mm] [MHz] [Ohm] [mT/MV] [1/m] [MHz] [MHz]

67.3 0 1 2801.5 43.06 193.5 65.27 2018.8 2801.5

60 08 1.13 2836.0 42.43 179.6 68.76 2110.9 2997.4

55 15 1.27 2825.6 42.25 172.3 71.78 2170.9 3158.1

50 23 1.46 2806.7 41.42 168.3 71.45 2243.3 3355.3

45 32 1.71 2805.4 38.59 157.4 71.16 2345.9 3597.5

Bmax


14 / 18Final Dimensions

R (race-track) (mm) 44

D (race-track) (mm) 33.6

Ratio (R+D)/R 1.76

Frequency (GHz) 2.815

RT / Q ( Ω) 37.8

Esp/Vdefl (1/m) ~72

Bsp/Vdefl (mT/MV) without damping

~160

100

120

140

160

180

200

0.90 1.10 1.30 1.50 1.70 1.90

ratio (long/short)

B_pe

ak /

V_de

f (m

T/M

V)

38

39

40

41

42

43

44

(R/Q

)*_T

(Ohm

)

B_peak / V_def [mT/MV]

R/Q* (Ohm)

B_peak / V_dev

150

155

160

165

170

175

180

185

190

1.4 1.6 1.8 2 2.2ratio (long/short)

B_p

eak

/ V_d

ev (

mT

/ MV)

JiaruGeoff


15 / 18Prototype Test

• Nb prototype for vertical test. (Result at J-Lab, presented by H. Wang)

• Cu model test.

Tab. Result with only beam-pipe

Experiment Simulationmode f / MHz Q_0 f / MHz

TM010 2402.23 5471 2400.3TM110_y 2800.14 14321 2806.5TE111_x 3062.31 15431 3066.5TE111_y 3104.09 15426 3128.1TM110_x 3811.79 4660 3806.3


16 / 18Damping Requirement for APS, ANL

Instability Thresholds from Parasitic Mode Excitation (by Y.Instability Thresholds from Parasitic Mode Excitation (by Y.--C C ChaeChae))APS parameters assumed: I = 100APS parameters assumed: I = 100--mA; E = 7 mA; E = 7 GeVGeVαα = = 2.8x102.8x10--44, (, (ωωss/2/2ππ) = 2 kHz, ) = 2 kHz, ννss = 0.0073, = 0.0073, ββxx = 20 m= 20 m

[1] A. Mosnier , Proc 1999 PAC.

[2] L. Palumbo, V.G. Vaccaro , M. Zobov , LNF -94/041 (P) (1994; also CERN 95 - 06, 331 (1995).


17 / 18Waveguide Damping on Beam Pipe

Co-axial damping as KEK-BWaveguide damping on accelerating cavity at J-LabWaveguide damping on deflecting cavity

Al model at Tsinghua for ALS at LBNL brief benchmark result on next page


18 / 18Qext Calculations in Time Domain

Method has also been benchmarked against measurements for a HOMdamped room temp cavity at J-Lab• MWS or MAFIA simulations in time domain• Waveguide boundary conditions at ports• Excite cavity from one RF (HOM) port or inside the cavity• Record and observe field (energy) decay as a function of time inside the cavity• External Q is computed from decay time

Excitation pulse E-Field decay

Benchmark at JBenchmark at J--LabLab


19 / 18

→→ Very good agreement !Very good agreement !

Two-Cell with Damping Waveguide at Tsinghua

With Waveguide LoadedMeasurements CST Simulation

f / GHz Q0 Qload Qext f / GHz Qext

LOMTM010 0 1.0401 10843 2030 2498 1.0400 2286

π 1.0435 10787 1709 2031 1.0438 1686

Deflecting ModeTM110 π y 1.4928 11514 10983 -- 1.4894 --

0 y 1.5037 11903 12107 -- 1.5013 --

Unwanted DipoleTM110 π x 1.4951 11233 673 716 1.4917 686

0 x 1.5045 11547 844 911 1.5025 930

HOM

TE111 0 y 1.8587 7898 159 163 1.8539 174 0 x 1.8529 7757 202 207 1.8465 196

π y 1.9293 6045 252 263 1.9278 260

π x 1.9260 6103 356 378 1.9243 338

Low power microwave measurements on the Al 2Low power microwave measurements on the Al 2--cell prototype cell prototype cavity with WG damping at Tsinghua University: external cavity with WG damping at Tsinghua University: external QQ


20 / 18Stub

• Threshold of LOM Q: < 500• CST Microwave Studio

– Eigenmode solver with external Q calculation

– Working mode frequency at 2763MHz because of end groups, need to be tuned later

– TM010 mode in cavity couples a resonant mode in stub. (detail next)

mode frequency

2000

2100

2200

2300

2400

2500

2600

2700

2800

2900

80 90 100 110 120 130 140

stublength / mm

frequ

ency

/ M

Hz 1

2345

Stub and one port instead of 2-ports

stub

Loaded port


21 / 18Different Stub lengthmode frequency

2200

2250

2300

2350

2400

2450

2500

80 90 100 110 120 130 140

stublength / mm

frequ

ency

/ M

Hz

23cell modestub mode approx.

external Q

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

80 90 100 110 120 130 140stublength / mm

Qex

t

23T domain

-1 5 0 -1 0 0 -5 0 0 5 0 1 0 0 1 5 00

0 . 5

1

1 . 5

2

2 . 5

3

3 . 5x 1 0

7

z / m m

M o d e 2

-150 -100 -50 0 50 100 150-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

z / m m

M od e 3

Frequency, Qext, field balance v.s. stublength

E-field on axis

Cell WG


22 / 18Points

• 2-unit coupling system: stub and cell– Field distribution in stub and cell depends on the frequency

difference. – Close frequency yields balanced field in the two unit and easy to

be damped through waveguide.• Optimized stub_length

– When Q*(R/Q) is smallest– A peak with very weak damping appears at a little longer than the

optimized value: might with wave node in wg on axis.– Shorter design is better than longer design for simulation error– Optimized stub length will change after the frequency of working

mode are tuned to 2815-MHz.


23 / 18Experiment on LOM damper

Sliding short to change stub length(with contact ring) One cell cavity with only the

LOM damper

Contact fingers around

With one port loaded

The other fit sliding short


24 / 18Bench Test / Summaryfrequency of 2 LOM's

2300

2350

2400

2450

2500

2550

2600

75 85 95 105 115stub length

f / M

Hz

Loaded Q

0

500

1000

1500

2000

2500

75 85 95 105 115stub length

Q_l

oad

• Agrees with theory• The optimized stub length: 97 mm

compared with 103 mm in simulation– Reason: the frequency is detuned

(~30 MHz) in simulation by HOM damper Q-Loaded and Q-ext

• ~200 Qext can be achieved with this LOM damper

• Stub coupling is stronger than 2-port loading (~600)


25 / 18Open Cell Waveguide Damping

• Open cell will get a field enhancement.– Comparable to field enhancement by endgroups– Goes up with enlarged slot

• Race-track slot and dog-bone slot (R. Rimmer’s idea) were studied.

Variable slot width (noted as slot_a)


26 / 18Open Cell Waveguide Damping

3 0 3 5 4 0 4 5 5 01 0 1

1 0 2

1 0 3

1 0 4

s lo t a / m mQ

ext o

f LO

M

B_max/V and Qext with only on-cell damper (w/o HOM end group)

Hot spot

• Slot_a around 45~50mm– With Qext of LOM less than 100– With peak B field of Working mode

around 200mT/MV – (~160 without slot) (~220 with only

HOM damper) (Bneck/Biris~0.8)• Two waveguides on each cell


27 / 18Multi-Cell?

• Start from cell-to-cell coupling / dispersion

dispersion curve

2600

2800

3000

3200

3400

3600

3800

4000

0 30 60 90 120 150 180phase adv / cell (Deg)

frequ

ency

Mode1Mode2

TM110TM110

TE111

TE111

Two mixed modes/passband


28 / 18Double Chain Model [1]

[1] K. Bane and R. Gluckstern, SLAC-PUB-5783

Dispersion curve

2700

2750

2800

2850

2900

2950

3000

0 30 60 90 120 150 180phase adv / cell (Deg)

frequ

ency

mode 1mode 21-chain TM1102-chain mode 1

• Double chain model agrees simulation result very well.• Coupling coefficient:

• k1 = 0.05 (TM)• K2 = 0.3 (TE)


29 / 18Summary

• Squashed cavity – Reduced magnetic field– Degenerate mode separation

• On-beam-pipe damping– Simulation and experiment shows stub coupling promising. With an

optimized stub length, get Qext~200• On-cell damping

– Field enhancement acceptable– Qext low to several tens– Need to check multipacting

• Multi-cell– Cell-to-cell coupling studied– High field enhancement– 2-cell/4-cell structure

• R. Rimmer’s talk for more information

Documents

Squashed Superconducting Deflecting Cavity for APS at ANL · 2013. 7. 28. · Jiaru Shi Defl. Cav. Workshop, SSRF, Apr.23-25, 2008 2/ 18 Deflecting RF Cavity R&D • Collaboration