Beam Chopper Development for Next Generation High Power Proton Drivers

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Beam Chopper Development forNext
GenerationHigh Power Proton Drivers
Michael A. Clarke-Gayther
RAL / FETS / HIPPI
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Outline

• Overview
• Fast Pulse Generator (FPG)
• Slow Pulse Generator (SPG)
• Slow wave electrode designs
• Summary

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Mike Clarke-Gayther (WP4 Fast Beam Chopper
MEBT)
Maurizio Vretenar (HIPPI WP coordinator) Alessandr
a Lombardi (WP4 Coordinator) 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)
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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.)
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.)
John Back (LEBT)
Christoph Gabor (Diagnostics) Ciprian Plostinar
(MEBT / DTL)
Jesus Alonso (ESS) Rafael Enparantza (ESS)
Javier Bermejo (ESS)
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Project History and Plan
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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
  support
• operating regime of hands on maintenance
  (1W/m)
• All existing NGPDs have suboptimal chopper designs

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A Fast Beam chopper for 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

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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

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Fast beam chopper schemes
Design Project Position Type Chopping Status
RAL ESS FETS MEBT Slow-wave Array Uni-directional Prototype
CERN SPL MEBT Slow-wave Uni- directional Advanced prototype
LANL/LBNL SNS MEBT LEBT Slow-wave Discrete Uni quad Installed tested
JAERI JPARC MEBT LEBT Cavity Induction Bi Longitudinal Installed tested?
FNAL X MEBT Slow-wave Uni Prototype
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The RAL Front-End Test Stand (FETS) Project / Key
parameters
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RAL Fast-Slow two stage chopping scheme
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3.0 MeV MEBT Chopper (RAL FETS Scheme A)
4.8 m
Chopper 1 (fast transition)
Beam dump 1
Chopper 2 (slower transition)
Beam dump 2
CCL type re-buncher cavities
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3.0 MeV MEBT Chopper (RAL FETS Scheme A)
2.4 m
Chopper 1 (fast transition)
CCL type re-buncher cavities
Beam dump 1 (low duty cycle)
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3.0 MeV MEBT Chopper (RAL FETS Scheme A)
2.4 m
Chopper 2 (slower transition)
Beam dump 2 (high duty cycle)
CCL type re-buncher cavities
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FETS Scheme A / Beam-line layout and GPT
trajectory plots
Losses 0.1 _at_ input to CH1, 0.3 on dump 1 0.1
on CH2, 0.3 on dump 2
Voltages Chop 1 /- 1.28 kV (20 mm gap) Chop
2 /- 1.42 kV (18 mm gap)
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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 ( p.mm.mr p.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
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Open animated GIF in Internet Explorer
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Fast Pulse Generator (FPG) development
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FPG / Front View
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FPG waveform measurement
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Slow Pulse Generator (SPG) development
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SPG beam line layout and load analysis
Slow chopper electrodes
Beam
16 close coupled slow pulse generator modules
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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
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SPG waveform measurement / HTS 41-06-GSM-CF-HFB
(4 kV)
Tr 11.3 ns
Tf 11.3 ns
SPG waveforms at 4 kV peak 0.2 ms / div.
SPG waveforms at 4 kV peak 50 ns / 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 _at_ 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 (n1 to 2) Limited Can be corrected
Timing stability (ns over 1 hour) 0.5 0.3 Yes Over temperature
Burst amplitude stability () 10, - 5 lt 10, -5 Yes Limited by power reg.
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Slow-wave electrode development
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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)
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On-axis field in x, y plane
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• Preliminary test assemblies
• Coaxial
• Helical
• Planar

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• 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.

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Coaxial test assembly
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Coaxial test assembly / Shapal-M version
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Helical test assembly
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Helical B2 / Short length prototype
UT-390 semi-rigid coaxial delay lines
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Helical B2 / CAD view
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Planar test assembly
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RAL Planar / Short length prototype
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RAL Planar / Short length prototype
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• 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

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• 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.

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