1 c-band linac development satoshi ohsawa 2004.feb.19lcpac
TRANSCRIPT
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C-Band Linac Development
Satoshi Ohsawa
2004.Feb.19 LCPAC
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Upgrade Requirements(1) KEKB SuperKEKB
Beam Energy (e–) 8.0 GeV -----> 3.5 GeV (e+) 3.5 GeV -----> 8.0 GeV !!
-> C-band accelerator modules
(2) KEKB SuperKEKBStored current (e–) 1.1 A -----> 9.4 A !! (e+) 1.5 A --> 2.6 A ---> 4.1 A !
-> e–: increase beam charge-> e+: flux concentrator (e+ capture effic.)
(3) Smaller e+ emittance to fit for IR & C-band module apertures
-> e+ damping ring
(4) Faster e+/e– mode-switching for Continunous e+/e– Injection -> separated e+/e– beam lines -> non-destructive beam monitoring
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Upgrade Scheme
e+ energy is boosted by the C-band (5712MHz) accelerator modules.
–8.0 GeV ~ 21 MV/m (S-band modules) x 46 m + 42 MV/m (C-band modules) x 185 m
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New C-band accelerator modulePresent S-band accelerator module
Wave guide
C-bandcompressor
PulseModul-ator
C-bandKly-stron
Wave guide
C-bandcompressor
PulseModul-ator
C-bandKly-stron
Wave guide
S-bandSLED
PulseModulator
S-bandKly-stron
C-band accelerating sectionsS-band accelerating sections
Linac Accelerator module
(From S-band To C-band)
41 MW4 s
40 MW2 s
40 MW2 s
Accel. field gradient = 21 MV/m Accel. field gradient = 42 MV/m
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C-Band Accelerator module
Wave guide
PulseModul-ator
C-bandKly-stron
1m C-band accelerating section
40 MW2 s
Accel. field gradient = 42 MV/m
First acceleration test
Target field gradient = 42 MV/m for e+ 8 GeV injection
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R & D strategy of accel. section
1. An accelerating section whose dimension is1/2-scale of that of the present S-band sectionis adopted as a first prototype in order to take the shortest path to the high power test of all the components in the C-band accelerator module.
2. No special cure considered against multi-bunch wake field effects (like damped structure or choke mode cavity) because the number of bunch is at most 2 e+ bunch intensity is low (1.2 nC) bunch interval is long (96 ns)
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C-band accel. section (First prototype)
54 regular cells 1m-longiris diameter 2a: 12.44 ~ 10.41 mmgroup velocity vg: 1.9 ~ 1.0 %shunt impedance r0: 74.8 ~ 85.3 M/mfield gradient Eacc: 41.2 ~ 39.0 MV/m
(assuming 40 MW klystron power)
Filling Time tF = 234 nsecAttn. Constant = 0.434
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C-band Test Stand
RF Window
High-power
Klystron
Modulator
SubBooster Klystron
Accelerating section
for High power test & RF processing of the components
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Test Stand (inside)
Dummy Load
Analyzer Magnet Faraday Cup
Accelerating section
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RF processing History
RF powerRF power
43.7 MW43.7 MW
Achieved!Achieved!
7/17 Start
9/5 Finish!
11C-band accel. section installed in KEKB linac (2003 September)
C-band sectionS-band section
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(A) Compact pulse modulator for klystron (350kV, 310A, 2sec. (flat top), 50Hz).
(B) 50MW high-power klystron (Toshiba E3748) assembly.
(C) Waveguide to the C-band accelerator section.
High power C-band (5712MHz) rf system
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Beam acceleration study
Energy gain measured by changing acceleration phase
with 43.8 MW x 0.5 s RF pulse
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C-band R & D items
• Klystron -> Toshiba E3746, High Power Test OK• Modulator -> compact (1/3 size), OK except inverter P.S. trouble
• Low power RF -> sub-booster OK, solid-state amp.?
• RF pulse compressor -> HPT in July 2004• Accelerating section -> 1st prototype 41 MV/m,
breakdown at input coupler
2nd prototype HPT in July 2004• Other RF components
– RF window HPT OK– Dummy load HPT OK– 3-dB hybrid power divider HPT OK– Wave guide flange HPT OK– RF gate valve under consideration
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0
5
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45
0 100 200 300 400 500
RF input [W]
RF o
utpu
t [M
W}
Es=42kVEs=40kVEs=38kV
Toshiba E3746 klystron assembly
Toshiba E3746 klystron (50MW) is adopted. Conventional 1:15 pulse-transformer (used at klystron gallery) is reused.
S-band C-band
RF output 41 MW 40 MW
Typical charging voltage
42 kV 41 kV
Typical applied voltage
290 kV 325 kV
Pulse duration 4 μs 2μs
Accelerating gradient
(21 MV/m) (42 MV/m)
Requirements for rf source
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Compact modulator
1.8 m4.7 m
By using invertor P.S., the modulator size can be 1/3 (4.7 m->1.8 m).
Present PFN and Thyratron are reused at new modulator.
Thyratron
Present modulatorCompact modulator
Inverter P.S.
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RF pulse compressor
• CERN-LIPS type of pulse compressor (TE038-mode cavity)
• Q0 = 142,000 (measured)
• Coupling beta = 6 ~ 7• Power multiplication ~ 3.4• Study with low power model
is under way to fix coupling hole dimension.
• High power test in July 2004Low powermodel
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Mix-mode rf window
Mix-mode (TE11+TM11) window with traveling wave in ceramic.
The electric field at the periphery is half of the S-band window.
4 - 1 / 4 " S W L4 - R c 1 / 8 ″ ネジ
FLANGE -FEMALEFLANGE -MALE
(78 .05 )(78 .05 ) (148 .4 )
3 0 4 . 5
Emag on yaxis vacuum
0
1
2
3
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5
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0 5 10 15 20 25 30 35 40 45
y [mm]
E [M
V/m
@50
MW
]
S total
S xy
C total
C xy
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Dummy load
Newly designed 2kW
Matsumoto-type dummy load
– 26 SiC cylinders– SiC diameter 12 mm
C-band dummy load heat distribution
0
0.5
1
1.5
0 50 100 150 200 250 300 350 400 450
distance from a bottom (mm)
heat
dis
trib
utio
n(n
orm
aliz
ed b
y pe
ak)
dummy No.1dummy No.3design value
Heat distribution
High power test OK up to 2 kW !
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Summary
• C-band R & D is in progress. High power test of the prototype C-band accelerator module has been performed since October 2003. Most of the components are working well.(Remaining issues)
Breakdown at input coupler
2nd prototype HPT in July 2004
Inverter P.S. troublesRF pulse compressor
HPT in July 2004