2004.Feb.19

LCPAC

C-Band Linac Development

Satoshi Ohsawa

1

2

Upgrade Requirements(1)
Beam Energy (e–)
(e+)

KEKB
SuperKEKB
8.0 GeV----->
3.5 GeV
3.5 GeV----->
8.0 GeV !!
-> C-band accelerator modules(2)Stored current (e–)
(e+)

KEKB
SuperKEKB
1.1 A----->
9.4 A !!
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3Upgrade 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

4

Linac Accelerator module(From S-band To C-band)
Present S-band accelerator module
Wave guide

Wave guideS-bandSLEDC-bandcompressor

41 MW
4 µs S-band

Pulse
Modulator

New C-band accelerator module

KlystronS-band accelerating sectionsAccel. field gradient = 21 MV/m

40 MW
2 µs Pulse

C-bandModul- Klystron
ator

Wave guideC-bandcompressor

40 MW

Pulse C-band
Modul- Kly- 2 µsstronatorC-band accelerating sections

Accel. field gradient = 42 MV/m

5C-Band Accelerator module
First acceleration test
Target field gradient = 42 MV/mfor e+ 8 GeV injection
Wave guide

40 MW
2 µsPulse
Modulator

C-bandKlystron

1m C-band accelerating section

Accel. field gradient = 42 MV/m

6R & 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 theshortest path to the high power test of all thecomponents in the C-band accelerator module.
2. No special cure considered against multi-bunchwake field effects (like damped structure or chokemode cavity) because

the number of bunch is at most 2e+ bunch intensity is low (1.2 nC)
bunch interval is long (96 ns)

7C-band accel. section (First prototype)54 regular cells
iris diameter 2a:group velocity vg:
shunt impedance r0:field gradient Eacc:

1m-long
12.44 ~ 10.41 mm
1.9~ 1.0%
74.8 ~ 85.3
MΩ/m
41.2 ~ 39.0
MV/m
(assuming 40 MW klystron power)

Filling Time tF = 234 nsec
Attn. Constant τ = 0.434

8C-band Test Standfor High power test & RF processingof the components
Modulator

RF Window

Accelerating
section
SubBooster
Klystron
High-power
Klystron9

Test Stand (inside)
Dummy Load

Accelerating
sectionAnalyzer
MagnetFaraday Cup10

RF processing History
7/17 Start

9/5 Finish!

RF power
43.7 MW
Achieved!

C-band accel. section installed in
KEKB linac (2003 September)

S-band section

C-band section

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High power C-band (5712MHz)
rf system(A) Compact pulse modulator
for klystron (350kV, 310A,
2µsec. (flat top), 50Hz).
(B) 50MW high-power klystron(Toshiba E3748) assembly.
(C) Waveguide to the C-band
accelerator section.

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Beam acceleration study
Energy gain measured bychanging acceleration phasewith 43.8 MW x 0.5 µs RF pulse

14C-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– Dummy load
– 3-dB hybrid power divider– Wave guide flange– RF gate valve

HPT OKHPT OKHPT OKHPT OK
under consideration

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Toshiba E3746 klystron assembly Toshiba E3746 klystron (50MW) is adopted.
 Conventional 1:15 pulse-transformer (used at klystron gallery) is reused.
Requirements for rf source
S-bandC-bandRF output

41 MW

40 MW

Typical charging
voltage

42 kV

41 kV

Typical applied
voltage

290 kV325 kV

Pulse duration

4 μs

2μs

Accelerating
gradient(21 MV/m)(42 MV/m)

45
40

RF output [MW}

3530
25

Es=42kV
Es=40kV
Es=38kV

2015
10
500

100

200

300

RF input [W]40050016Compact modulator
 By using invertor P.S., the modulator size can be 1/3 (4.7 m->1.8m).
 Present PFN and Thyratron are reused at new modulator.
Inverter P.S.

Compact modulator

Present modulator
Thyratron
4.7ｍ

1.8ｍ

17RF pulse compressor

Low powermodel• CERN-LIPS type of pulsecompressor(TE038-mode cavity)• Q0 = 142,000 (measured)• Coupling beta = 6 ~ 7• Power multiplication ~ 3.4• Study with low power modelis under way to fix couplinghole dimension.
• High power test in July 2004

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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.
Emag on yaxis vacuumS total

6S xy
C total

E [MV/m @50 MW]

5４−Ｒｃ１／８″ネジ

C xy

432４−１／４" ＳＷＬ1FL A N G E- F E M AL E

F LA N G E -M A L E00( 78 . 0 5 )(1 4 8 . 4)
３０４．５

( 7 8 .0 5 )

51015

20
25y [mm]30354045

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Dummy load
Newly designed 2kW
Matsumoto-type
dummy load
– 26 SiC cylinders– SiC diameter 12 mm
High power test OK
up to 2 kW !
heat distribution(normalized by peak)C-band dummy load heat distribution

1.5Heat distribution

1dummy No.1
dummy No.3
design value

0.5

00 50 100150200250300350400450
distance from a bottom (mm)20Summary• C-band R & D is in progress. High power test of theprototype C-band accelerator module has been
performed since October 2003. Most of thecomponents are working well.
(Remaining issues)
Breakdown at input coupler
2nd prototype HPT in July 2004

Inverter P.S. troubles
RF pulse compressor
HPT in July 2004