Beam Chopper Development for Next Generation High Power Proton Drivers

M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007

Beam Chopper Development for

Next GenerationHigh Power Proton Drivers

Michael A. Clarke-GaytherRAL / FETS / HIPPI


Overview

Fast Pulse Generator (FPG)

Slow Pulse Generator (SPG)

Slow – wave electrode designs

Summary

Outline

Overview


Maurizio Vretenar(WP Coordinator)Alessandra Lombardi(WP4 Leader)Luca Bruno, Fritz CaspersFrank Gerigk, Tom KroyerMauro PaoluzziEdgar Sargsyan, Carlo Rossi

Mike Clarke-Gayther (WP4 Fast Beam Chopper & MEBT)

Chris Prior (WP Coordinator) Ciprian Plostinar (WP2 & 4 N-C Structures / MEBT)Christoph Gabor (WP5 / Beam Dynamics)

Overview


John Back (LEBT)

Aaron Cheng (LPRF)Simon Jolly (LEBT Diagnostics)Ajit Kurup (RFQ)David Lee (Diagnostics) Jürgen Pozimski (Ion source/ RFQ)Peter Savage (Mechanical Eng.)

Mike Clarke-Gayther (Chopper / MEBT)Adeline Daly (HPRF sourcing & R8)Dan Faircloth (Ion source)Alan Letchford (RFQ / (Leader)Jürgen Pozimski (Ion source / RFQ) Chris Thomas (Laser diagnostics)

Christoph Gabor(Laser diagnostics)Ciprian Plostinar (MEBT / DTL)

Javier BermejoPierpaolo Romano(LEBT / Beam stop)

Overview


Project History and Plan

Overview


A Fast Beam chopper for

Next Generation Proton Drivers / Motivation

To significantly reduce beam loss at trapping / extraction• Enables ‘Hands on’ maintenance (1 Watt / m)

To support complex beam delivery schemes• Enables low loss ‘switchyards’ and duty cycle control

To provide beam diagnostic function• Enables low duty cycle (i.e. ‘low risk)’ accelerator tuning

Overview


Design Project Position Type Chopping Status

RALESS & FETS

MEBTSlow-wave

& ArrayUni-

directionalPrototype

CERN SPL MEBT Slow-waveUni-

directionalAdvanced prototype

LANL/LBNL SNSMEBT

& LEBT

Slow-wave

& DiscreteUni & quad

Installed

& tested

JAERI JPARCMEBT

& LEBT

Cavity &

Induction

Bi &

Longitudinal

Installed

& tested?

FNAL ‘X’ MEBT Slow-wave Uni Prototype

Fast beam chopper schemes

Overview


The RAL Front-End Test Stand (FETS) Project / Key parameters

Overview


RAL ‘Fast-Slow’ two stage chopping scheme

Overview


3.0 MeV MEBT Chopper (RAL FETS Scheme A)

Chopper 1 (fast transition)

Chopper 2 (slower transition)

‘CCL’ type re-buncher cavities

4.6 m

Beam dump 1

Beam dump 2

Overview



Chopper 1 (fast transition)


2.3 m

Beam dump 1 (low duty cycle)

Overview



Chopper 2 (slower transition)


2.3 m

Beam dump 2(high duty cycle)

Overview


FETS Scheme A / Beam-line layout and GPT trajectory plots

Losses:0.1 % @ input to CH1, 0.3% on dump 10.1% on CH2, 0.3% on dump 2

Voltages:Chop 1: +/- 1.28 kV (20 mm gap)Chop 2: +/- 1.42 kV (18 mm gap)

Overview


KEY PARAMETERS SCHEME A

ION SPECIES H-

ENERGY (MeV) 3.0

RF FREQUENCY (MHz) 324

BEAM CURRENT (mA) 40 - 60

NORMALISED RMS INPUT EMITTANCE IN X / Y / Z PLANES

( π.mm.mr & π.deg.MeV)

0.25 / 0.25 / 0.18

RMS EMITTANCE GROWTH IN X / Y / Z PLANES (%) 6 / 13 / 2

CHOPPING FACTOR (%) 30 - 100

CHOPPING EFFICIENCY (%) 99.9

FAST CHOPPER PULSE: TRANSITION TIME / DURATION / PRF/ BURST DURATION / BRF

2 ns / 12 ns / 2.6 MHz / 0.3 – 2 ms / 50 Hz

FAST CHOPPER ELECTRODE EFFECTIVE LENGTH / GAPS (mm) 450 x 0.82 = 369 / 20

FAST CHOPPER POTENTIAL(kV) ± 1.3

SLOW CHOPPER PULSE: TRANSITION TIME / DURATION /

PRF/ BURST DURATION /

BRF

12 ns / 250 ns – 0.1 ms 1.3 MHz / 0.3 – 2 ms /

50 Hz

SLOW CHOPPER EFFECTIVE LENGTH / GAPS (mm) 450 x 0.85 / 18

SLOW CHOPPER POTENTIAL (kV) ± 1.5

POWER ON FAST / SLOW BEAM DUMPS (W) 150 / 850

OPTICAL DESIGN CODE(S) IMPACT / TRACEWIN

/ GPT

Overview


Open animated GIF in Internet Explorer


Fast Pulse Generator (FPG) development

FPG development


9 x Pulse generator cards

High peak power loads

Control and interface

Combiner


Power supply



1.7 m

FPG / Front View

RAL FPGSpecified by:

M. Clarke-Gayther Supplied by:

Kentech InstrumentsWallingford, UK

CERN FPGSpecified by:M. Paoluzzi Supplied by:

FID TechnologySt. Petersburg,

Russia

FPG development


Pulse Parameter FETS Requirement Measured Compliancy Comment Amplitude (kV into 50 Ohms) ± 1.4 ± 1.5 Yes Scalable Transition time (ns) ≤ 2.0 Trise = 1.8, Tfall = 1.2 Yes 10 – 90 % Duration (ns) 10 - 15 10 - 15 Yes FWHM Droop (%) 2.0 in 10 ns 1.9 in 10 ns Yes F3dB ~ 300 kHz Repetition frequency (MHz) 2.4 2.4 Yes Burst duration (ms) 0.3-1.5 1.5 Yes Burst repetition frequency (Hz) 50 50 Yes Duty cycle ~ 0.27 % Post pulse aberration (%) ± 2 ± 5 No Reducible Timing stability (ps over 1 hour) ± 100 ± 50 Yes Peak to Peak Burst amplitude stability (%) + 10, - 5 + 5, - 3 Yes

FPG waveform measurement


Slow Pulse Generator (SPG) development

M. A. Clarke-Gayther RAL/FETS/HIPPI

SPG development

CARE-07 October 30th 2007

16 close coupled ‘slow’ pulse generator modules

Slow chopperelectrodes

Beam

SPG beam line layout and load analysis


SPG development


Prototype 8 kV SPG euro-cassette module / Side view

Low-inductance HV damping resistors

8 kV push-pull MOSFET switch module

High voltagefeed-through(output port)

Axial cooling fans

Air duct

0.26 m


SPG development


SPG waveforms at ± 4 kV peak & 50 ns / div.

SPG waveform measurement / HTS 41-06-GSM-CF-HFB (4 kV)

SPG waveforms at ± 4 kV peak & 50 μs / div.

Tr =12.0 ns

Tf =10.8 ns

Pulse Parameter FETS Requirement Measured Compliancy Comment

Amplitude (kV into 50 Ohms) ± 1.5 ± 4.0 Yes ± 4 kV rated

Transition time (ns) ~ 12.0 Trise ~ 12, Tfall ~ 11 Yes 500 pulses

Duration (μs) 0.23 – 100 0.17 – 100 Yes FWHM

Droop (%) 0 0 Yes DC coupled

Repetition frequency (MHz) 1.3 1.3 Yes

Burst duration @ 1.2 MHz 0.3 – 1.5 ms 1 ms Close Scalable

Burst repetition frequency (Hz) 50 25 Close Scalable

Post pulse aberration (%) ± 5 ≤ ± 5 Yes Adjustable

Pulse width stability (ns) ± 0.1 8.2 ns (n=1 to 2) Limited Can be corrected

Timing stability (ns over 1 hour) ± 0.5 ± 0.3 Yes Over temperature

Burst amplitude stability (%) + 10, - 5 < + 10, -5 Yes 0.4 ms burst


Slow-wave electrode development



Where:

Transverse extent of the beam: L2Beam transit time for distance L1: T(L1) Pulse transit time in vacuum for distance L2: T(L2) Pulse transit time in dielectric for distance L3: T(L3) Electrode width: L4

For the generalised slow wave structure:Maximum value for L1 = V1 (T3 - T1) / 2Minimum Value for L1 = L2 (V1/ V2)T(L1) = L1/V1 = T(L2) + T(L3)

The relationships for field (E), and transverse displacement (x), where q is the electronic charge, is the beam velocity, m0 is the rest mass, z is the effective electrode length, is the

required deflection angle, V is the deflecting potential, and d is the electrode gap, are:

zqmE

2

0tan

d

VE 2

0

2

2

m

zEqx

‘E-field chopping / Slow-wave electrode design



Strategy for the development of RAL slow–wave structures

Modify ESS 2.5 MeV helical and planar designs • Reduce delay to enable 3 MeV operation• Increase beam aperture to ~ 20 mm• Maximise field coverage and homogeneity• Simplify design - minimise number of parts• Investigate effects of dimensional tolerances• Ensure compatibility with NC machining practise• Identify optimum materials

Modify helical design for CERN MEBT• Shrink to fit in 95 mm ID vacuum vessel



RAL Planar A2 / Prototype



RAL Planar A2 / Prototype



RAL Planar A2 / Pre-prototype



RAL Planar A2 / Pre-prototype

Coaxialinterfaceadapter

Extendeddielectricconnector(SMA)



Helical structure B2 / Prototype

UT-390 semi-rigidcoaxial delay lines



Helical structure B2 / Prototype



Helical structure B2 / Pre-prototype



Coaxial interfaceadapter

Extended dielectricconnector (SMA)

Helical structure B2 / Pre-prototype



‘On-axis field in x, y plane

CERN Planar:(F. Caspers,T. Kroyer)

Supplied by:Kyocera Corp.

Japan



Simulation of Helical B structure in the T & F domain

Summary


FPG• Meets key specifications

SPG• 4 kV version looks promising

Slow-wave electrode designs• Planar and Helical designs now scaled to 3.0 MeV• Beam aperture increased to 19.0 mm• HF models of components with trim function• Analysis of coverage factor• Analysis of effect of dimensional tolerances• Identification of optimum materials / metallisation• Identification of coaxial components and semi-rigid cable• Designs compatible with NC machining practice

Summary


Some final comments and the next steps

The development of FETS optical scheme A has lowered the working voltage requirement for the FPG and SPG. The existing FPG is now compliant, and the results of recent tests on a 4 kV SPG switch module are promising. Modification of the existing 8 kV euro-cassette design will enable the 4 kV switch to be tested at the specified duty cycle.

The RAL slow wave electrode designs are mechanically more complex than the CERN design, but simulations indicate that E-field coverage factor and transverse uniformity should be superior. The design of planar and helical pre-prototype modules is nearing completion, and results of HF tests should be available by the year end.

Summary


HIPPI WP4: The RAL† Fast Beam Chopper Development Programme Progress Report for the period: July 2005 – December 2006

M. A. Clarke-Gayther †

† STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK

EU contract number RII3-CT-2003-506395 CARE-Note-2007-002-HIPPI

References


M Clarke-Gayther, ‘Slow-wave chopper structures for next generation high power proton drivers’, Proc. of PAC 2007, Albuquerque, New Mexico, USA, 25th – 29th June, 2007, pp.1637-1639

M Clarke-Gayther, G Bellodi, F Gerigk, ‘A fast beam chopper for the RAL Front-End Test Stand’, Proc. of EPAC 2006, Edinburgh, Scotland, UK, 26th - 30th June, 2006, pp. 300-302.

M Clarke-Gayther, ‘Fast-slow beam chopping for next generation high power proton drivers’, Proc. of PAC 2005, Knoxville, Tennessee, USA, 16th – 20th May, 2005, pp. 3637-3639

M Clarke-Gayther, ‘A fast beam chopper for next generation proton drivers’, Proc. of EPAC 2004, Lucerne, Switzerland, 5th – 9th July, 2004, pp. 1449-1451

M Clarke-Gayther, ‘Slow-wave electrode structures for the ESS 2.5 MeV fast chopper’, Proc. of PAC 2003, Portland, Oregon, USA, 12th - 16th May, 2003, pp. 1473-1475

F Caspers, ‘Review of Fast Beam Chopping’, Proc. of LINAC 2004, Lubeck, Germany, 16 th – 20th August, 2004, pp. 294-296.

F Caspers, A Mostacci, S Kurennoy, ‘Fast Chopper Structure for the CERN SPL’, Proc. of EPAC 2002, Paris, France, 3rd – 7th June, 2002, pp. 873-875.

Beam Chopper Development for Next Generation High Power Proton Drivers

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