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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

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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

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1

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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

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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