Klystron Modulator for Proton Driver

Chris Jensen

• Why does Proton Driver need modulators

• Overview of pulse power concepts

• Description of three possible modulators

• Update on status of SMTF modulators

Feburary 2, 2005 2

Why modulators ?• Need high power RF to

accelerate beam • Need RF amplifiers

– Klystron (e- Beam - RF Converter)– Require high voltage ( 130 kV )– Limited Spark Energy ( 20 J )

• Need Peak Power to drive klystron– Modulator converts wall power to

peak power– Klystron Efficiency is 50%– Limit average power dissipated

Feburary 2, 2005 3

Pulse Power Concepts

• Two time regimes– Pulse Compression

• Peak vs. Average• Components Ratings

– Some need Peak

– Some need Average

– How many need both?

• Reliable Operation

Feburary 2, 2005 4

Pulse Forming Network

• Linac is one example

• Output shaped by network

• Each capacitor section provides peak energy for fraction of pulse length

• Pulse Length is 125 us

• How can size / cost be reduced for long pulses

Klystron

PulseTransformer

Charging Supply

Feburary 2, 2005 5

Pulse Forming Network

Feburary 2, 2005 6

Pulse Switching Mode Supply

• SNS Modulator one example

• 1.3 ms, 60 Hz, 10 MW peak

• Output shaped by switching / regulating

• High voltage output needs filter and rectifier

• High Frequency / Voltage Transformer

Rectify &Filter

Main Cap Bank

Switch20kHz, 2ms

Charging SupplyCapacitor Bank

PulseTransformer

Klystron

Feburary 2, 2005 7

Feburary 2, 2005 8

Bouncer Modulator

• Built for Tesla Test Facility in 1994

• Output shaped by bouncer network

• Invented by Quentin Kerns

Klystron

PulseTransformer

2000 µF

Charging SupplyCapacitor Bank

Bouncer

330 µH

1400 µFMain Cap Bank

Feburary 2, 2005 9

Bouncer Modulator

• Switch connects main capacitor bank to transformer during pulse.

• Transformer steps up voltage to 120kV/130A (12:1)

• Main capacitor bank discharges by 20% during pulse

• “Bouncer” circuit compensates for cap bank droop.

Feburary 2, 2005 10

FNAL Original Modulator Circuit

Network

0.08IGBTIGBT

Pulse

1:12

160

Undershoot

Transformer

FNAL Tesla Version II ModulatorCircuit Diagram

1400 µF

Klystron

Crowbars

ZOVZOV

Protection

370 µH

50 µH

Switches - 12 Main + 3 Backup

100 µF

Clipper

Klystron

Bouncer 2000 µF

330 µH

Main Cap Bank

Capacitor BankCharging Supply

Feburary 2, 2005 11

Feburary 2, 2005 12

Feburary 2, 2005 13

Feburary 2, 2005 14

Feburary 2, 2005 15

Improved Bouncer ModulatorBuilt for DESY by industry

Feburary 2, 2005 16

Feburary 2, 2005 17

Bouncer Modulator for SMTF

• Incorporate New Capacitor Technology– Self Healing Hazy Polypropylene

• Incoporate New Switch Technology– IGBTs have improved over 10 years

• Pulse Length increased to 4 ms (from 2ms)– Modular construction for flexibility

Feburary 2, 2005 18

Feburary 2, 2005 19

SMTF Modulator Status

• Pulse Transformers for SMTF on order• Main Capacitor Bank from AVX / TPC

– Volume is 20% of original film/paper

– Cost is 50% of original film/paper

• Bouncer Capacitors and Inductors out for bid– No significant change in requirements or size

– Added power saved cost incentive to inductor

• Switch is in Design Stage– SLAC collaborating with design