2005.Feb.22

KEKB Review

C-band R & D status
for SuperKEKB
Kamitani Takuya

1 /17

Status at the last KEKB Review (Feb-2004)

2 /17

Linac C-band Test Module #4-4A(C-band components was installed in Sep-2003 and had been operated for 5 months)• 2856 x 2=> 5712 MHz• 1/3-size of S-band modulator • Output power in operation
max 43 MW x 0.5 µsec
• inverter Power supply(max 2.0 µsec)• Heating and IGBT
breakdown problem

Pulse compressor• TE038 cavity• Low power test

RF windowModulator• Mix-mode (TE11+TM11)• Half E-field of S-band pill box
type window• 160 MW at Test StandSub booster
Klystron(Mitsubishi PV5101)

High-power
Klystron(Toshiba E3746)

Dummy load

• SiC block array type
• 100 MW at Test StandBeam
model of S-band section
Accelerating section •• Half-scale
Field gradient 38 MV/m at 43 MW KLY output(CKM001)• Breakdown problem

Present Status (Feb-2005)

3 /17• Things achieved in recent 12 months

Linac C-band Test Module #4-4A(Pulse compressor was installed in Sep-2004 and has been operated for 5 months)• Heating andIGBT Breakdown
problem almost fixed• Output power in operation
12 MW x 2.0 µsec
(max 43 MW)

RF window • 300 MW at Test StandModulator

Pulse compressor (installed in Sep-2004)• 200 MW output at Test Stand• 56 MW in operation

Sub booster
Klystron(Mitsubishi PV5101)

High-power
Klystron(Toshiba E3746)• 17 months operation
since installation

Under fabrication
CKK001

CKK002

CKM002

CMM001

Dummy loadBeam

42 MV/m at 56 MW
Accelerating section • Field gradientpulse
compressor output(CKM001)• Breakdown problem

Klystron & modulator

4 /17• Klystron and modulator have been operated since Sep-2003• C-band modulator is 1/3 size of S-band modulator
with inverter DC power supply.
• Heating => (1) Improve cooling, (2) Ohmic loss reduction• IGBT breakdown => (1) Larger margin in current and voltage,(Insulated Gate Bipolar Transistor) (2) Improved gate driver circuit• No trouble since Sep-2004

Inverter DC PS

4.7ｍ
S-band modulator & klystron

1.8ｍ
C-band modulator & klystron5 /17

RF window
1. Mix-mode (TE11+TM11)
RF window with travelingwave in ceramic part
2. Electric field strength ishalf of S-band pill box
type RF window

9:;<

3. 300 MW transmission
power achieved withresonant ring!"'!"&$!"&!"%$!"%!"!$!"!
!"#$!

%!#=67$"( $"($ $") $")$ $"* $"*$+,-./-012345678

RF windowRF pulse compressor
1. SLED-type compressor, but
TE038 mode cavity insteadof TE015(Q0 = 132,000,coupling beta = 6.6).
2. 200 MW output power isachieved at Test Stand.
3. Power multiplication factor
is 4.7 at peak.

6 /17(SKIP: SuperKEKB Injector Pulse compressor)

Accelerating section (CKM001; ser#=1)

7 /17

1. Fabricated at Mitsubishi Heavy Industry
2. Installed in linac #4-4A module(Aug-2003)

3. Operated with RF power directly fromklystron (till Jun-2004)
4. Pulse compressor installed (Aug-2004)
5. Operated with Pulse compressor

S-band section(until now)

• Half-scale model of S-band section(1-m long, 54 cavity cells)••

traveling-wave, disk-loaded structure
2/3-π phase advance per cell

C-band section• quasi-constant gradient• formed by cupper electroplating•single-port coupler (field asymmetry not corrected)• thin (1mm) coupler irisEnergy gain measurement
1. Field gradient is estimatedby measuring energy gainof the C-band module with
3-GeV e- beam at the Linacend
2. Field gradient ~ 38 MV/m at
KLY output power 43 MW without
pulse compressor
in Jun-2004

3. Field gradient ~ 42 MV/mat KLY output power 12 MWwith pulse compressor(peak power ~ 56 MW)
in Dec-2004

8 /17

9 /17

RF breakdown (CKM001)
1. Breakdown occurs typically
5 times/hour @ 43 MW
2. It mostly occurs around the input
coupler
3. Surface damage was observed
around the iris of the input-coupler,
the 1st disk and a the bottom of
the coupler cavity (metallic dust ?)OutputcouplerInput
coupler

Breakdown location estimated fromthe timings of transmitted and reflected waves

coupler-iris insidecoupler-iris outside

first disk

10 /17Strategy of accelerating section development
Power from Klystron
40 MW x 2.0 us

Design C-band
accelerator module
for SuperKEKB
Power input for each section(including WG loss)
80 MW

Power from Pulse compressor
188 MW x 0.5 us
50 MW22 MW

Disk aperture 2a =14.5->12.5->10.5mm
Group velocity vg/c = 3 -> 2 -> 1 %2m-long sections

1.

Development of coupler structure / regular cell cavities

2.

Demonstration of operation as a whole C-band module(installation only in summer shutdown)

3.

Establish fabrication technique at KEKForthcoming accelerating sections

11 /17Fabricator

Disc2aCoupler

CupperElectroplating

Completion(1)
CKM001MHI

12.5->
10.5

1-port, Edge iris 1-mm thick,
2π/3 mode cell coupler(S-band section half-scale model)High speed

MHIJuly-2003Now inoperation(2)
CKK001

KEK 12.5->
10.5

1-port, Edge iris 4-mm thick,arched end, non-standard cell coupler
full-length iris => wave guide width

Low speedMar-2005(3)
CKK002

KEK 14.5(CI)1-port, Smooth iris 4-mm thick,axis-offset,
full-length iris => 2π/3 mode cell coupler
Electropolishing of coupler surface

Low speed(4)
CKM002

MHI

12.5
->
10.5

1-port, Partly smooth iris 3-mm thick,
2π/3 mode cell coupler

High speed

12.5(CI)

1-port, Partly smooth iris 3-mm thick,2π/3 mode cell coupler

PeriodicReverse(5)
MHI
CMM001

NomuraMay-2005

NomuraJun-2005

MHIMHI

Jun-2005

Accelerating section (CKK001; ser#=2)
1. Fabricated at KEK
2. Thick (4 mm) iris
3. Arched waveguide end
4. Non-standard coupler celllength (full length iris)

VSWR ~ 1.05
(after electroplating)1.17

12 /17

Accelerating section (CKK002; ser#=3)
1. Under fabrication at KEK
2. Smooth shape coupler iris
3. Standard coupler cell lengthand full length iris
4. Coupler axis offset
for field asymmetry correction

5. Coupler cavity surface
treatmentby Electropolishing
6. For highest power input
largest disk aperture cells
group velocity vg/c = 3 %(for CKM001 vg/c = 1 ~ 2 %)7. Constant impedance

13 /17

Accelerating section (CKM002; ser#=4)

14 /17

1. Slight modification of CKM001 (#1) in coupler iris shape=> thick and round edge
2. Under fabrication at MHI
3. To be completed in June-2005
CKM001 coupler• thin (1mm) iris• sharp edge•

CKM002 coupler• thick (3mm) iris
• round edge(outside surface)• same as CKM001(inside surface)

CMM001 (ser#=5) is almost same as CKM002 except forelectroplating method and constant impedancePlanned configuration (Aug-2005)
Linac C-band Test Module #4-4A(will start operation in this configuration in Aug-2005)

Modulator

RF window
Pulse compressor

Sub booster
Klystron(Mitsubishi PV5101)

High-power
Klystron(Toshiba E3746)

3-dB Hybrid

Dummy loads

Beam
CKK002 CKM001

CKM002 CKK001

Accelerating sections

15 /17

Summary (Things achieved in recent 12 months)

16 /17

1. Heating and IGBT breakdown problem of the inverter power supply isalmost fixed and the modulator has been operating for 5 months withno trouble.
2. Mix mode RF window achieved 300 MW transmission power at TestStand.
3. RF pulse compressor has been fabricated, achieved 200 MW output
power at Test stand and installed in C-band test module #4-4A in theKEKB linac.
4. Field gradient in the accelerating section is estimated by beam
acceleration study to be 42 MV/m with klystron output power 12 MWand with rf power compression (x 4.7 times at peak).
5. Four new accelerating sections are in fabrication and will be installedin Sep-2005

Future development in accelerating section
1. Two port coupler,
if single port coupler is not satisfactory against breakdowns
even with smooth-shaped iris.

2. New types of coupler structure
if smooth-shaped iris coupler is not satisfactory.
A) mode converter type couplerB) wave guide coupler

3. 2m-long structureA)
B)
C)

one 2m-long structure=> difficult in fabrication and RF measurement
two 1m-long structures connected with couplers andwaveguides=> present design layout but expensive
two 1m-long structures directly connected with cavity cells

17 /17