Beam Chopper Development for Next Generation High Power Proton Drivers
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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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Overview
Fast Pulse Generator (FPG)
Slow Pulse Generator (SPG)
Slow – wave electrode designs
Summary
Outline
Overview
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Project History and Plan
Overview
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
The RAL Front-End Test Stand (FETS) Project / Key parameters
Overview
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
RAL ‘Fast-Slow’ two stage chopping scheme
Overview
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
3.0 MeV MEBT Chopper (RAL FETS Scheme A)
Chopper 1 (fast transition)
‘CCL’ type re-buncher cavities
2.3 m
Beam dump 1 (low duty cycle)
Overview
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
3.0 MeV MEBT Chopper (RAL FETS Scheme A)
Chopper 2 (slower transition)
‘CCL’ type re-buncher cavities
2.3 m
Beam dump 2(high duty cycle)
Overview
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Fast Pulse Generator (FPG) development
FPG development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
9 x Pulse generator cards
High peak power loads
Control and interface
Combiner
9 x Pulse generator cards
Power supply
9 x Pulse generator cards
9 x Pulse generator cards
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI
SPG development
CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI
SPG development
CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Slow-wave electrode development
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
RAL Planar A2 / Prototype
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
RAL Planar A2 / Prototype
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
RAL Planar A2 / Pre-prototype
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
RAL Planar A2 / Pre-prototype
Coaxialinterfaceadapter
Extendeddielectricconnector(SMA)
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Helical structure B2 / Prototype
UT-390 semi-rigidcoaxial delay lines
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Helical structure B2 / Prototype
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Helical structure B2 / Pre-prototype
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Coaxial interfaceadapter
Extended dielectricconnector (SMA)
Helical structure B2 / Pre-prototype
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
‘On-axis field in x, y plane
CERN Planar:(F. Caspers,T. Kroyer)
Supplied by:Kyocera Corp.
Japan
Slow-wave electrode development
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
Simulation of Helical B structure in the T & F domain
Summary
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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
M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30th 2007
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.
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