high-current srf cavity design€¦ · 11july2005 dave meidlinger (msu, nscl) 2005 srf workshop...
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11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
HIGH-CURRENT SRF CAVITYDESIGN
Dave MeidlingerTerry Grimm
Walter Hartung
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
OUTLINE
• Introduction• Primary Concerns that Direct Cavity Design• 6-Cell Elliptical Cavity• 2-Cell Injection Cavity• TM012 Cavity• Summary
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
Objective
• High current ERL (100’s mA) (10 MeV-100’s MeV)
• Simplified HOM damping
• Simplified cavity and cryomodule
• Lower cost
Electron source
Electron cooling / FEL
Beam dump
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
Issues Driving Cavity Design
Transverse multipass/multibunch beam breakup
HOM power dissipation
AVGlossHOM IqkP =
( )QRth Qf
I 1∝
m
mm Q
Rfk ⎟⎟⎠
⎞⎜⎜⎝
⎛=
2π
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
Bunch Frequency
• Setting fbunch = fRFCan simplify HOM damping for a large enough diameter beam pipe.
i.e. all dangerous HOMs above cutoff (low Qs)
Lowers bunch charge for same average current
bunch
AVGlossAVGlossHOM f
IkIqkP2
==
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
frequency
fRF
frequency
CUTOFFfRF
frequency
CUTOFFfRF
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
frequency
fRF
frequency
CUTOFFfRF
frequency
CUTOFFfRF
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
frequency
fRF
frequency
CUTOFFfRF
frequency
CUTOFFfRF
( )QRth Qf
I 1∝
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
HOM Qs
• Trapped modes and HOM couplers – 2100 MHz (JLAB FEL)– Q~ 106, Ith ~ 10 mA
• Above cutoff– Damp in beampipe with ferrite, coupler or wall
losses– Q~ 103 , Ith ~ 10 A
( )QRth Qf
I 1∝
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
Elliptical Cavity Designs
• 100's mA beam current• 1.5 GHz• TM01 cutoff ~1.95fRF and TE11 cutoff ~1.5fRF
• 6o wall angle• Epk / Bpk equals TeSLA value• 2 cells β > 0.50• 6 cells β = 1.0
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
Transit Time Factors
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
v / c
TT
6-Cell
2-Cell
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
Cavity Figures of Merit
2-Cell 6-Cell
Ep / EA - 2.16 2.19Bp / EA mT / (MV/m) 4.59 4.68R / Q Ω 165 535
Geometric β - 0.81 1.0
275
3.9
6Number of Cells - 2
Cell-to-cell Coupling % 2.8
Geometrical Factor Ω 228
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
2-Cell Surface Fields
0 5 10 15 20 25
distance along surface (cm)
|B|
|E|
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
6-Cell Surface Fields
0 10 20 30 40 50 60
distance along surface (cm)
|B||E|
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
-50 -40 -30 -20 -10 0 10 20 30 40 50
axial distance (cm)
Electric Field Profile
2.7% fieldunflatness
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
6-Cell BNL Ampere Class TeSLA CEBAF
Ep / EA - 2.19 2.0 2.00 2.56Bp / EA mT / (MV/m) 4.68 5.8 4.26 4.56R / Q Ω 535 404 1036 482.5
5
Ω
%
-
273.8
3.29
Number of Cells 6 5 9
Cell-to-cell Coupling 3.9 3 1.9
Geometrical Factor 275 225 270
6-Cell Elliptical
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
TM012 Cavity
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
TM012 Cavity
• AdvantagesSimple shape
Easier fabricationBetter film depositionLow loss factor
Single cellEasier tuning
• DisadvantagesHigh peak magnetic fieldsDamping parasitic modes below the accelerating modeLow shunt impedance
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
TM012 Cavity
TM012Ep / EA - 3.06Bp / EA mT / (MV/m) 8.40
Voltage Gain MV 2Ep MV / m 4.8Bp mT / (MV/m) 13.19
R / Q Ω 55
k|| V / pC 0.37
Frequency MHz 353
beam pipe radius cm 17
Geometrical Factor Ω 476
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
TM012 SOLEILEp / EA - 3.06 2Bp / EA mT / (MV/m) 8.40 4.5
Voltage Gain MV 2 2Ep MV / m 4.8 9.42Bp mT / (MV/m) 13.19 21.2
R / Q Ω 55 90
k|| V / pC 0.37 0.75
Frequency MHz 353 353
beam pipe radius cm 17 13
Geometrical Factor Ω 476
TM012 Cavity
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
TM012 SOLEILEp / EA - 3.06 2Bp / EA mT / (MV/m) 8.40 4.5
Voltage Gain MV 2 2Ep MV / m 4.8 9.42Bp mT / (MV/m) 13.19 21.2
R / Q Ω 55 90
k|| V / pC 0.37 0.75
Frequency MHz 353 353
beam pipe radius cm 17 13
Geometrical Factor Ω 476
TM012 Cavity
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
Summary
• Objective: 100's mA of beam current with a simplified design
• Concept: Fill every RF bucket so that all dangerous HOMs are above cutoff.
• 2-Cell injection cavity and 6-Cell cavity designed for this purpose.
• Fabrication of 2-cell prototype to be completed by end of 2005.
11July2005 Dave Meidlinger (MSU, NSCL)2005 SRF Workshop
HIGH-CURRENT SRF CAVITYDESIGN
Dave MeidlingerTerry Grimm
Walter Hartung