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Beam Chopper Development for Next Generation High Power Proton Drivers. Michael A. Clarke-Gayther. RAL / FETS / HIPPI. Outline. Overview Fast Pulse Generator (FPG) Slow Pulse Generator (SPG) Slow – wave electrode designs Summary. Mike Clarke-Gayther (WP4 Fast Beam Chopper & MEBT).

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Beam Chopper Development for Next Generation High Power Proton Drivers

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Beam chopper development for next generation high power proton drivers

Beam Chopper Development forNext GenerationHigh Power Proton Drivers

Michael A. Clarke-Gayther

RAL / FETS / HIPPI


Beam chopper development for next generation high power proton drivers

Outline

  • Overview

  • Fast Pulse Generator (FPG)

  • Slow Pulse Generator (SPG)

  • Slow – wave electrode designs

  • Summary


Beam chopper development for next generation high power proton drivers

Mike Clarke-Gayther

(WP4 Fast Beam Chopper & MEBT)

Maurizio Vretenar

(WP Coordinator)

Alessandra Lombardi

(WP4 Leader)

Luca Bruno, Fritz Caspers

Frank Gerigk, Tom Kroyer

Mauro Paoluzzi

Edgar Sargsyan, Carlo Rossi

Chris Prior (WP Coordinator)

Ciprian Plostinar

(WP2 & 4 N-C Structures / MEBT)

Christoph Gabor (WP5 / Beam Dynamics)


Beam chopper development for next generation high power proton drivers

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)

Aaron Cheng (LPRF)

Simon Jolly (LEBT Diagnostics)

Ajit Kurup (RFQ)

David Lee (Diagnostics)

Jürgen Pozimski (Ion source/ RFQ)

Peter Savage (Mechanical Eng.)

Christoph Gabor

(Laser diagnostics)

Ciprian Plostinar

(MEBT / DTL)

Javier Bermejo

Pierpaolo Romano

(LEBT / Beam stop)

John Back (LEBT)


Beam chopper development for next generation high power proton drivers

Project History and Plan


Beam chopper development for next generation high power proton drivers

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


Beam chopper development for next generation high power proton drivers

Fast beam chopper schemes


Beam chopper development for next generation high power proton drivers

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


Beam chopper development for next generation high power proton drivers

RAL ‘Fast-Slow’ two stage chopping scheme


Beam chopper development for next generation high power proton drivers

3.0 MeV MEBT Chopper (RAL FETS Scheme A)

4.6 m

Chopper 1 (fast transition)

Beam dump 1

Chopper 2 (slower transition)

Beam dump 2

‘CCL’ type re-buncher cavities


Beam chopper development for next generation high power proton drivers

3.0 MeV MEBT Chopper (RAL FETS Scheme A)

2.3 m

Chopper 1 (fast transition)

‘CCL’ type re-buncher cavities

Beam dump 1 (low duty cycle)


Beam chopper development for next generation high power proton drivers

3.0 MeV MEBT Chopper (RAL FETS Scheme A)

2.3 m

Chopper 2 (slower transition)

Beam dump 2

(high duty cycle)

‘CCL’ type re-buncher cavities


Beam chopper development for next generation high power proton drivers

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

Voltages:

Chop 1:+/- 1.28 kV (20 mm gap)

Chop 2:+/- 1.42 kV (18 mm gap)

Losses:

0.1 % @ input to CH1, 0.3% on dump 1

0.1% on CH2, 0.3% on dump 2


Beam chopper development for next generation high power proton drivers

Open animated GIF in Internet Explorer


Beam chopper development for next generation high power proton drivers

Fast Pulse Generator (FPG) development


Beam chopper development for next generation high power proton drivers

High peak power loads

Control and interface

Power supply

9 x Pulse generator cards

1.7 m

9 x Pulse generator cards

Combiner

9 x Pulse generator cards

9 x Pulse generator cards

FPG / Front View

RAL FPG

Specified by:

M. Clarke-Gayther

Supplied by:

Kentech Instruments

Wallingford, UK

CERN FPG

Specified by:

M. Paoluzzi

Supplied by:

FID Technology

St. Petersburg,

Russia


Beam chopper development for next generation high power proton drivers

FPG waveform measurement


Beam chopper development for next generation high power proton drivers

Slow Pulse Generator (SPG) development


Beam chopper development for next generation high power proton drivers

SPG beam line layout and load analysis

Slow chopper

electrodes

Beam

16 close coupled ‘slow’ pulse generator modules


Beam chopper development for next generation high power proton drivers

Prototype 8 kV SPG euro-cassette module / Side view

Axial cooling fans

Air duct

High voltage

feed-through

(output port)

0.26 m

8 kV push-pull MOSFET switch module

Low-inductance HV damping resistors


Beam chopper development for next generation high power proton drivers

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

Tr =12.0 ns

Tf =10.8 ns

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

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


Beam chopper development for next generation high power proton drivers

Slow-wave electrode development


Beam chopper development for next generation high power proton drivers

‘E-field chopping / Slow-wave electrode design

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:

Where:

Transverse extent of the beam: L2

Beam 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) / 2

Minimum Value for L1 = L2 (V1/ V2)

T(L1) = L1/V1 = T(L2) + T(L3)


Beam chopper development for next generation high power proton drivers

  • 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


Beam chopper development for next generation high power proton drivers

RAL Planar A2 / Prototype


Beam chopper development for next generation high power proton drivers

RAL Planar A2 / Prototype


Beam chopper development for next generation high power proton drivers

RAL Planar A2 / Pre-prototype


Beam chopper development for next generation high power proton drivers

RAL Planar A2 / Pre-prototype

Coaxial

interface

adapter

Extended

dielectricconnector

(SMA)


Beam chopper development for next generation high power proton drivers

Helical structure B2 / Prototype

UT-390 semi-rigid

coaxial delay lines


Beam chopper development for next generation high power proton drivers

Helical structure B2 / Prototype


Beam chopper development for next generation high power proton drivers

Helical structure B2 / Pre-prototype


Beam chopper development for next generation high power proton drivers

Helical structure B2 / Pre-prototype

Coaxial interface

adapter

Extended dielectricconnector (SMA)


Beam chopper development for next generation high power proton drivers

‘On-axis field in x, y plane

CERN Planar:

(F. Caspers,

T. Kroyer)

Supplied by:

Kyocera Corp.

Japan


Beam chopper development for next generation high power proton drivers

Simulation of Helical B structure in the T & F domain


Beam chopper development for next generation high power proton drivers

  • 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


Beam chopper development for next generation high power proton drivers

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.


Beam chopper development for next generation high power proton drivers

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


Beam chopper development for next generation high power proton drivers

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, 16th – 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.


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