Accelerator Laboratory

Flux Concentrator
Modulator Development
KEKB injector linac
Mitsuo Akemoto
March 5, 2013
18th KEKB Accelerator Review Commi7ee
KEKB Accelerator Review Commi7ee/FC
modulator Development/Akemoto1

Accelerator Laboratory

Table of Contents
1. Modulator design
2. Prototype 6 kA modulator for test study
3. 12 kA modulator for operaLon model
4. Future plan
5. Summary
KEKB Accelerator Review Commi7ee/FC
modulator Development/Akemoto2Requirements of Flux Concentrator
Accelerator Laboratory••••

Half‐sine 5 µs pulse
12 kA peak current
Amplitude stability 0.3%(p‐p)
50 pps

30 m
Pulse cable

Flux Concentrator
Current PulseI12 kA

Flux Concentrator(~ 1 µH)

KEKB Accelerator Review Commi7ee/FC
modulator Development/Akemoto

5 µst
3

Principle of Operation
Accelerator Laboratory•Half sine wave generated by L‐C resonant circuit•Use thyratron as a switch•Used at SLAC and IHEP
Load current(L)R
I peak = V0 "CL

T= " LC
2C!

L!

Basic circuit
KEKB Accelerator Review Commi7ee/FC
modulator Development/Akemoto4Strategy of FC Modulator
Accelerator Laboratory

Prototype 6 kA modulator speciﬁcaLon

FC modulators are developed in two steps.
•Prototype 6 kA modulator• KEKB klystron modulator is revised to FC modulator• Established technology•Low‐cost and high maintainability•Next step is 12 kA modulator
PFNParameter

Speciﬁca8on

Capacitance

0.5 µF

Load inductance~ 1 µH

Total inductance~ 3 µH

Charging voltage

17 kV

Peak current

6 kA

Pulse width

5 µs

RepeLLon rate

50 Hz

Capacitor bank
PFN
R‐C snubber circuit
10 parallel
30 m coaxial cables

KEKB modulator for S-band klystron22.5 kV, 4.8 kA, 5.6µs pulses at 50 pps

Prototype 6 kA Modulator
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FC5

Prototype 6 kA Modulator
Accelerator Laboratory

Thyratron
DiodesCapacitor
10 CoaxialCables
Resistors
SwitchingPower Supply
Klystron modulator
PFN unit

Capacitor bank unit

Inside view of the modulator
KEKB Accelerator Review Commi7ee/FC
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Front side view of the modulator
6R-C Snubber Circuit
Accelerator Laboratory

Load current waveforms simulated by a computer code Micro‐Cap 9
Without R‐C snubber circuit

C =50nF

R=2.5ΩC=100nF

C =150nF

7KEKB Accelerator Review Commi7ee/FC
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6kA Prototype Modulator Tests
Accelerator Laboratory

Typical load current waveform at a charging voltage of 17 kV

Load Current(A)

8000
6000
4000
2000

Equivalent inductance loadand C‐R circuit

0-200002

468101214Use of 10 parallel Cables
30 m, 25 Ω, 40 kV Coaxial Cable

Time(µs)

A peak current of 6000 A with a width of 5 µs has been successfully generated
at 50 pps
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12 kA Modulator Design
Accelerator Laboratory

12 kA modulator speciﬁcaLon•Based on a prototype modulator design
Using two thyratrons•Easy maintenance, low-cost•Will be complete at the end of Nov.

Parameter

Speciﬁca8on

Capacitance

1.0 µF

Load inductance~ 1 µH

Total inductance~ 1.5 µH

Charging voltage

17 kV

Peak current

12 kA

Pulse width

5 µs

RepeLLon rate

50 HzFC

12kA Modulator

20 Parallel 30m, coaxial cables
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12 kA Modulator Design
Accelerator Laboratory•The capacitors, two thyratron units, other all parts without a charging
PS and control units are housed in the KEKB modulator discharge
cabinet.

KEKB modulator

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Discharge cabinet

10Possibility of Thyratron Replacement
Accelerator Laboratory•Thyratron is short-life.
•Develop a solid-state switch to replace thyratrons•Improve the reliability of the modulator•PPJ Company

25 kV, 5kA, 10µs, 10 Hz
6Px10S SI-Thyristors Switch
Size : 300(W)x150(D)x500mm(H)

SI-Thyristors Switch
KEKB Accelerator Review Commi7ee/FC
modulator Development/Akemoto11Summary
Accelerator Laboratory•A prototype 6 kA modulator has been built by revising from theexisting S-band modulator.
• A peak current of 6 kA with a width of 5 µs has been successfully
generated at 50 pps.
•12 kA modulator is under design, which is based on prototype
modulator design, and will be completed at the end of Nov.
• We have a plan to develop a solid-state switch to replace thyratorn
to improve the reliability of the modulator.

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