9th KEKB Acc. Review Committee Feb.17,2004

C-band linac progress: rf source
Accelerator Laboratory

KEK –High Energy Accelerator Research Organization
Accelerator Laboratory

Shinichiro MICHIZONO, for the KEKB-Linac RF GroupOverview of C-band rf system
Rf system
LLRF
Driver klystron (Subbooster:SB)
High power klystronCompact modulator
RF window / resonant ring
Performance at KG #44
Future works
19th KEKB Acc. Review Committee Feb.17,2004

Overview of C-band rf system
Accelerator Laboratory

 C-band rf system from #3 to #5 sector
 Forty eight klystrons are installed (instead of 24 S-band klystrons)
RFSystemDiagramC-bandPlan(example)
Counter

MAINDRIVE LINE

CW
571 MHz

2856MHz

C-band Waveguide Driving Line

Ref. Signal Generator(FMD-30)

MR

E/O

508 MHz114 MHz571 MHz

Trigger
System5712MHz

Driver

30m
15m

100m

60kW S-band
Klystron
SUB DRIVELINE(39D)

Coaxial Lines
30m
40m
5m
5m
SB-A

SB-B

SB-CIΦA

SB-1
1 kW
Amp.
System

114
MHz
SHB1

ElectronGun

571
MHz
SHB2

IΦA

SB3-2

50MW S-band
KlystronHigh Power
ATT/Phase
Shifter

10kW
AMP.

100kWC-band
Klystron
SUB DRIVE LINE(WG)

80m1 kWAmp.
Systeme-O/E

Optical Lines

100m

20m

SUB-BOOSTER3-1

SUB-BOOSTER 2

10 MHz

SB4-1

SB4-2

SB5-1

SB5-2

50MC-band
Klystron

SLEDSLEDSector 2

Sector 3-1

TargetPrebuncher Buncher ACCGuide

SectorA

Sector B

SectorC Sector 1

e+ e-ACC

ACC
Sector 3-2

Sector 4-1 Sector4-2 Sector 5-1 Sector5-2

48 C-band klystrons29th KEKB Acc. Review Committee Feb.17,2004

LLRF system
Accelerator Laboratory

 S-band -> (frequency doubler) -> C-band A lot of S-band LLRF system is reused. (pulse modulator, trigger,….)2μs3

9th KEKB Acc. Review Committee Feb.17,2004

SB klystronAccelerator Laboratory

Klystron and magnet
 Retune the existing C-band 200 kW klystron for weather
observation station (MELCO).
 Driver klystron (SB) can deliver >100 kW (35 kV).
 Same modulator and HV supply to S-band system is used.
250

42.6kV mag:22.3A/22.3A/22.3A
35kV mag:17.0A/17.0A/17.5A
27kV mag 15.6A/16.8A/11.7A

SBK modulator
Pin=0.16W
mag:22.3A/22.3A/22.3A

300

200

150
200

Pout[kW]

Pout[kW]250

100150100505000.01

00.1

1Pin[W]

102030

40
V[kV]

504

9th KEKB Acc. Review Committee Feb.17,2004

Toshiba E3746 klystron assembly
Accelerator Laboratory

 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

Typicalcharging
voltage

42 kV

41 kV

Typical applied
voltage

290 kV325 kV

Pulse duration

4 μs

2μs

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

4540

RF output [MW}353025Es=42kV
Es=40kV
Es=38kV

201510500100200300

RF input [W]40050059th KEKB Acc. Review Committee Feb.17,2004

Compact modulator (1)Accelerator Laboratory

 Compact modulator is necessary to install 48 units.
Present Layout of Unit Sector

Proposed C-band Modulator Configuration
Present Configuration ofModulator and Klystron
Klystron
Modulator
Modulator

Proposed Layout of C-band Unit Sector

Inverter

40 MW
Klystron

Modulator

40 MW
Klystron

600RF and Coil P/SControl

Control

560

Modulator
600
Control

800

Klystron

Proposed Configuration

Beam69th KEKB Acc. Review Committee Feb.17,2004

Compact modulator (2)Accelerator Laboratory

 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.
Inverter P.S.

Compact modulator

Present modulator
Thyratron
4.7ｍ

1.8ｍ

7

9th KEKB Acc. Review Committee Feb.17,2004

Inverter Power Supply Development
Accelerator Laboratory

Specifications• Output voltage• Output power• Voltage regulation• Efficiency• Power factor• Switching frequency• Input voltage• Cooling• Weight• Size

50 kV(max.)
30 kJ/s
±0.1%
89%
86%
33 kHz420 V, 3 Phase, 50 Hz, AC
Water, 4.5 liters/min.
170 Kg19” rack mount
449mm(H), 480mm(W), 630mm(D)Switching Power Supply (TDP)89th KEKB Acc. Review Committee Feb.17,2004

Inverter Power Supply Development-2
Accelerator Laboratory

IGBT

HV
Transformer

ON/OFF
Control

3.0

PFN
Capacitors

StrageCapacitor

Es= 45 kV, fr=50 pps

2.5

Gate Driving Circuit

Pulse Modulator

Current
Feedback

Control Circuit

VoltageFeedback

Charging Current(A)AC 420 V
Inductor for improving
Input PowerPower Factor

2.060µs

30µs( 33 kHz)7.8

7.85

1.5
1.0
0.5
0.0-0.5

Local / RemoteControls and Monitors

7.7

7.75

7.9Time(ms)7.95

Block Diagram of Switching Power Supply

2.5PFN Voltage(kV)

2
1.5
10.5
0-0.5
-10-5

05

10Time(ms)

15

20

25

Charging Current(A)50Problem40
1. Heating of HV tank30
• Cooling improvement
20• Reduction of ohmic loss(winding wire)10
Tank temperature over 130˚C ----> below 90˚C
2. IGBT breakdown due to dual trigger pulse (Nov.,2003) 0• Redesign the IGBT gate driving circuit-1099th KEKB Acc. Review Committee Feb.17,2004

Applied pulse waveform
Accelerator Laboratory

 Flat top: 2 μs,
 PFN Impedance: 5 ohms
 Pulse-transformer 1:15
 350 kV at maximum
 Measured flatness 1.3%(p-p)
 Stability ±0.15%

500 V/div.
1 ms/div.

130V
Ch.1:charging voltage(42 kV)

Ch.2:charging current
Ch.1:10 kV/div.
Ch.2:0.4A/div.
4 ms/div.

current

4.5 μsRf output
2μs
Applied voltage:333 kV

1.3%(p-p)

7.5 kV/div.
400 ns/div.

10

9th KEKB Acc. Review Committee Feb.17,2004

Test standAccelerator Laboratory

 C-band system is installed in the test stand.
 RF window, dummy load and acceleration structure were tested.

119th KEKB Acc. Review Committee Feb.17,2004

Breakdown of rf window
Accelerator Laboratory

 Breakdown of the rf windows induces
1) vacuum leak to the acceleration structure2) rf reflection at the window High reliability is required for the rf window.
 The breakdown is initiated by the edge-emission of the ceramics.
→ Lower the electric field at periphery of ceramics (triple-junction).

Triple junction and multipactor

Broken window

Localized melting

Surface discharge
129th KEKB Acc. Review Committee Feb.17,2004

R&D of c-band rf window
Accelerator Laboratory

 About Sixty S-band rf windows are successfully operated in KEKB linac.
(MTBF > 40,000 h.) Electric fileds should be less than rf windows used in S-band linac.
 Mix-mode window (TE11+TM11) enables to lower the edge electric field.
 Five parameters are optimized for lower electric fields and traveling wave inceramic.

S-bandC-band

1.35
1.3

3.7

3.1

Electric field at edge of theceramics [MV/m@50MW]

1.7

Maximum electric field on theceramics [MV/m@50MW]

5.5

3.7

Band width [MHz]（VSWR<1.2)

600

210

0.8

VSWR

Electric field at center of theceramics [MV/m@50MW]

1.4

210MHz

1.25
1.2
1.15
1.1
1.05
1
5.6

5.65

5.7
5.75
frequency [GHz]

5.8

5.85

13

9th KEKB Acc. Review Committee Feb.17,2004

Mix-mode rf window
Accelerator Laboratory 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 vacuum
S total

6S xy
C total

E [MV/m @50 MW]

5４－Ｒｃ１／８″ネジ

C xy

432４－１／４＂ＳＷＬ

1FLANGE-FEMALE

FLANGE-MALE

00510152025303540

y [mm](78.05)(148.4)３０４．５(78.05)14

9th KEKB Acc. Review Committee Feb.17,2004

Low level measurements
Accelerator Laboratory

 The low power measurements are carried out by bead perturbation method.
 The electric fields measured are similar to calculation.

Z=0Z=-90

Electric field [arb. unit]

1210864
measuredcalculation

20-90-80-70-60-50-40z [mm]-30-20-10015

9th KEKB Acc. Review Committee Feb.17,2004

Resonant ring
Accelerator Laboratory

 In order to examine the rf window, resonant ring is assembled.
 Resonant ring consists of hybrid (14dB) and waveguides.
 Power multiplication ratio is about 18.
 Rough tuning: spacer in the ring (±5mm)
 Fine tuning: frequency (±5MHz)
 Operation frequency for rf window test is 5710.2MHz(5712MHz-1.8MHz).
 Evacuated by NEG and ion pumps. (<10-6 Pa)

16

9th KEKB Acc. Review Committee Feb.17,2004

Assembly of resonant ring
Accelerator Laboratory

 C-band rf system from #3 to #5 sector
 Forty eight klystrons are installed (instead of 24 S-band klystrons)

17

9th KEKB Acc. Review Committee Feb.17,2004

Resonant ring in the shield
Accelerator Laboratory Both sides of rf window are evacuated with NEG and ion pumps.

18

9th KEKB Acc. Review Committee Feb.17,2004

Resonant ring in the shield
Accelerator Laboratory Both sides of rf window is evacuated with NEG and ion pumps.

19

9th KEKB Acc. Review Committee Feb.17,2004

Results at resonant ring (1)Accelerator Laboratory

 Maximum operation power of 160 MW (2μs), corresponding to fullreflection from the load at the rf power of 40 MW.
 Radiation level is <1 μSv/h, much less than S-band window.

RRVAC[Pa]RRP

Resonant ring transmission power (160 MW)

RR VAC pressure [Pa]1.E-05

1.E-06

1.E-07
13:50

14:50
May 6200
180
160
140120
100
8060
40
200

RR Pf [MW]Klystron output (8.7 MW)

15:51

20

9th KEKB Acc. Review Committee Feb.17,2004

Results at resonant ring (2)Accelerator Laboratory

 RF losses at rf window are measured.
 The loss is almost same to the S-band window.
 The C-band window ceramics is 25% thicker than S-band ceramics.
 50 MW 2μs,50 pps operation will be safe from the view point ofheating.
14.000S-TWwinφ84 7.6t

S-SLACwinφ84 3.2t

12.000P loss [W]

10.000y = 0.9584x
R2 = 0.996

8.000

C-Mixwinφ78 4t

6.000
4.000
2.000
0.000
0.00

2.00

4.00

6.00
8.00
P average [kW]

10.00

12.00

14.00

219th KEKB Acc. Review Committee Feb.17,2004Installation to klystron gallery (#44)
Accelerator Laboratory

Vac(A)

Vac(A)

 RF system moved to klystron gallery on Sep.,2003.
 Vacuum pumps are located near the rf windows.
(klystron / mix-mode window)

Vac(B)IP

Vac(acc.)Rf window

IP22

9th KEKB Acc. Review Committee Feb.17,2004

Operation status @ #44
Accelerator Laboratory

 RF operation continues more than 100 days.
 Trips caused by the modulator are 52 for 110 days operation.
 After the exchange of thyratron, the stability increases drastically (Nov.3,2003).
 Inverter PS is exchanged on Nov.5,2003 in order to improve the IGBT gate driving circuit.
 After that the modulator runs rather stably. (but under development)
HV OCP 52 trips/110days

Due to conditioning
50

Number of trips(Sep.30,2003-Feb.11,2004)

IGBT circuit improvement

45
40

11,34635

Vacuum (A)20

30

Vacuum (B)14

Vacuum (acc.)

147

modulator

52Es [kV]VSWR

Due to improper thyratron operation

25
20
15
10
50
1-Oct

31-Oct30-Novdate

30-Dec29-Jan28-Feb23

9th KEKB Acc. Review Committee Feb.17,2004

Future works
Accelerator Laboratory

 2nd klystron assembly has been tested since Jan.,2004.
 The conventional oil tank (for S-band) is reused.
 Since the outer diameter is same to the magnet,reinforcement is required.
 High power test (upto 50 MW) for the klystron assembly(pulse transformer, dielectric insulator,capacitive divider (max.350kV) ….) will continue.
 High power resonant ring test will be carried out upto
200 MW. (next April)

φ600

φ600

24