M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Beam Chopper Development for Next...

M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16th September 2008

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


Maurizio Vretenar(HIPPI WP coordinator)Alessandra Lombardi(WP4 Coordinator)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)


John Back (LEBT)

Saad Alsari (RF)Simon Jolly, Ajit Kurup (RFQ)David Lee (Laser Diagnostics) Jaroslav Pasternack (UK-NF)Jürgen Pozimski (Ion source/ RFQ)Peter Savage (Mechanical Eng.)

Mike Clarke-Gayther (Chopper / MEBT)Dan Faircloth, Scott Lawrie (Ion source)Alan Letchford (RFQ / FETS coordinator)Mike Perkins (Ion source power supplies)Jürgen Pozimski (Ion source / RFQ)Pierpaolo Romano (Beam stop) Philip Wise (Mechanical Eng.)

Christoph Gabor(Diagnostics)Ciprian Plostinar (MEBT / DTL) Javier Bermejo (ESS)

Jesus Alonso (ESS)Rafael Enparantza (ESS)

Overview


Project History and Plan

Overview


A Fast Beam chopper for

Next Generation Proton Drivers (NGPDs) / Motivation

Key enabling component for all NG synchrotron and accumulator ring based proton drivers

• Beam loss during trapping is a ‘show stopper’

• Order of magnitude reduction in loss required to supportoperating regime of ‘hands on maintenance’ (1W/m)

• All existing NGPDs have suboptimal chopper designs

Overview



Next Generation Proton Drivers (NGPDs) / Motivation

FETS will test a unique, UK designed, fast beam chopper with the potential to be the first to demonstrate efficient operation on ring based NGPDs for spallation neutron sources and neutrino factories

Overview



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

4.8 m

Beam dump 1

Beam dump 2

Overview



Chopper 1 (fast transition)


2.4 m

Beam dump 1 (low duty cycle)

Overview



Chopper 2 (slower transition)


2.4 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


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

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

UK-NF 16th September 2008

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 & 0.2 ms / div.

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 @ 1.3 MHz 0.3 – 1.5 ms 1 ms Close Limited by cooling

Burst repetition frequency (Hz) 50 25 Close Limited by cooling

Post pulse aberration (%) ± 5 ≤ ± 5 Yes Damping dependent

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 Limited by power reg.

Tr =11.3 ns

Tf =11.3 ns


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



‘On-axis field in x, y plane



Preliminary test assemblies

Coaxial Helical Planar



Preliminary test assemblies

The manufacture and test of these preliminary assemblies will provide important information on the following: Construction techniques. NC machining and tolerances.Selection of machine-able ceramics and of suitable copper and aluminium alloys. Electroplating and electro-polishing. Accuracy of the 3D high frequency design code.


Coaxial test assembly



Coaxial test assembly / Shapal-M version



Helical test assembly



Helical B2 / Short length prototype

UT-390 semi-rigidcoaxial delay lines



Helical B2 / CAD view


Planar test assembly



RAL Planar / Short length prototype

Summary


FPG• Meets key specifications

SPG• 4 kV version looks promising

Slow-wave electrode designs• Measurements on coaxial test assembly have:

• Verified accuracy of high frequency modelling code• Tested effect of mechanical tolerances • Tested machining properties of selected ceramic material

• Measurements on helical test assembly have:• Tested effect of strip-line tolerances and electro-polishing• Probed limitations of NC machining practice

Summary


Slow-wave electrode designs (continued):

• Planar test assembly – design in progress – to test:• Machining properties of ceramic support pillars• Strip-line clamping and positioning tolerances

The design and manufacture of the subsequent planar and helical ‘short length’ prototype structures, will build on the experience gained from the preliminary test assemblies, and should facilitate the choice of a candidate design for the full scale structure.

References


HIPPI WP4: The RAL† Fast Beam Chopper Development Programme Progress Report for the period: January 2007 – June 2008

M. A. Clarke-Gayther

STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK

EU contract number RII3-CT-2003-506395 CARE-Report-08-016-HIPPI

References


M Clarke-Gayther, ‘The development of a fast beam chopper for next generation high power proton drivers’, Proc. of EPAC 2008, Genoa, Italy, 23rd – 27th June, 2008, pp. 3584-3586.

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.

M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Beam Chopper Development for Next...

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