Beam Chopper Development for Next Generation High Power
Beam Chopper Development for Next Generation High Power Proton Drivers Michael A. Clarke-Gayther RAL / FETS / HIPPI M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Outline Ø Overview Ø Fast Pulse Generator (FPG) Ø Slow Pulse Generator (SPG) Ø Slow – wave electrode designs Ø Summary M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview Mike Clarke-Gayther (WP 4 Fast Beam Chopper & MEBT) Chris Prior (WP Coordinator) Ciprian Plostinar (WP 2 & 4 N-C Structures / MEBT) Christoph Gabor (WP 5 / Beam Dynamics M. A. Clarke-Gayther RAL/FETS/HIPPI Maurizio Vretenar (WP Coordinator) Alessandra Lombardi (WP 4 Leader) Luca Bruno, Fritz Caspers Frank Gerigk, Tom Kroyer Mauro Paoluzzi Edgar Sargsyan, Carlo Rossi CARE-07 October 30 th 2007
Overview Mike Clarke-Gayther (Chopper / MEBT) Adeline Daly (HPRF sourcing & R 8) 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) John Back (LEBT) M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview Project History and Plan M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview A Fast Beam chopper for Next Generation Proton Drivers / Motivation Ø To reduce beam loss at trapping and extraction • Enable ‘Hands on’ maintenance (1 Watt / m) Ø To support complex beam delivery schemes • Enable low loss ‘switchyards’ and duty cycle control Ø To provide beam diagnostic function • Enable ‘low risk’ accelerator development M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview Fast beam chopper schemes Design Project Position Type Chopping Status RAL ESS & FETS MEBT Slow-wave & Array Unidirectional Prototype CERN SPL MEBT Slow-wave Unidirectional Advanced prototype LANL/LBNL SNS MEBT Slow-wave & LEBT & Discrete Uni & quad Installed & tested JAERI JPARC MEBT & LEBT Cavity & Solenoid Bi & Longitudinal Installed & tested? FNAL ‘X’ MEBT Slow-wave Uni Prototype M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview The RAL Front-End Test Stand (FETS) Project / Key parameters M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview RAL ‘Fast-Slow’ two stage chopping scheme M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview 3. 0 Me. V 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 M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview 3. 0 Me. V MEBT Chopper (RAL FETS Scheme A) 2. 3 m Chopper 1 (fast transition) ‘CCL’ type re-buncher cavities Beam dump 1 (low duty cycle) M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview 3. 0 Me. V MEBT Chopper (RAL FETS Scheme A) 2. 3 m Chopper 2 (slower transition) Beam dump 2 (high duty cycle) ‘CCL’ type re-buncher cavities M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview FETS Scheme A / Beam-line layout and GPT trajectory plots Voltages: Chop 1: Chop 2: +/- 1. 28 k. V (20 mm gap) +/- 1. 42 k. V (18 mm gap) M. A. Clarke-Gayther RAL/FETS/HIPPI Losses: 0. 1 % @ input to CH 1, 0. 3% on dump 1 0. 1% on CH 2, 0. 3% on dump 2 CARE-07 October 30 th 2007
Overview Open animated GIF in Internet Explorer M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Overview KEY PARAMETERS SCHEME A ION SPECIES H- ENERGY (Me. V) 3. 0 RF FREQUENCY (MHz) 324 BEAM CURRENT (m. A) 40 - 60 NORMALISED RMS INPUT EMITTANCE IN X / Y / Z PLANES ( π. mm. mr & π. deg. Me. V) 0. 25 / 0. 18 RMS EMITTANCE GROWTH IN X / Y / Z PLANES (%) 6 / 13 / 2 CHOPPING FACTOR (%) 30 - 100 CHOPPING EFFICIENCY (%) FAST CHOPPER PULSE: TRANSITION TIME / DURATION / PRF/ BURST DURATION / BRF FAST CHOPPER ELECTRODE EFFECTIVE LENGTH / GAPS (mm) FAST CHOPPER POTENTIAL(k. V) SLOW CHOPPER PULSE: TRANSITION TIME / DURATION / PRF/ BURST DURATION / BRF SLOW CHOPPER EFFECTIVE LENGTH / GAPS (mm) SLOW CHOPPER POTENTIAL (k. V) POWER ON FAST / SLOW BEAM DUMPS (W) OPTICAL DESIGN CODE(S) M. A. Clarke-Gayther RAL/FETS/HIPPI 99. 9 2 ns / 12 ns / 2. 6 MHz / 0. 3 – 2 ms / 50 Hz 450 x 0. 82 = 369 / 20 ± 1. 3 12 ns / 250 ns – 0. 1 ms 1. 3 MHz / 0. 3 – 2 ms / 50 Hz 450 x 0. 85 / 18 ± 1. 5 150 / 850 IMPACT / TRACEWIN / GPT CARE-07 October 30 th 2007
Fast Pulse Generator (FPG) development M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
3. 0 Me. V MEBT Chopper (RAL FETS Scheme A) 2. 3 m Chopper 1 (fast transition) ‘CCL’ type re-buncher cavities Beam dump 1 (low duty cycle) M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
FPG development FPG / Front View 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 M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
FPG development FPG waveform measurement M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
FPG development FPG duty cycle induced baseline shift compensation FPG baseline shift for five bunch chopping at 324 MHz Timing schematic: Compensation ‘off’ @ 1 μs & 0. 5 k. V/div M. A. Clarke-Gayther Circuit schematic: Duty cycle droop compensation Timing schematic: Compensation ‘on’ @ 1 μs & 0. 5 k. V/div RAL/FETS/HIPPI CARE-07 October 30 th 2007
FPG / Summary Measured performance parameters, for the FPG indicate that the design is generally compliant with the FETS specification. Passive techniques to reduce post-pulse aberration can be implemented when the precise configuration of the load circuit is determined. A scheme to compensate for the duty cycle induced baseline shift, for the case of a fixed or slowly varying duty cycle, has been described, and indicates that the resulting residual baseline shift due to LF cut-off can be balanced around the zero volt level, giving values of ± 1. 5 % for five bunch chopping in the FETS MEBT. For the case of a rapidly varying duty cycle, duty cycle induced baseline shift can be eliminated, by utilising an FPG with a bipolar output pulse, resulting in alternate beam bunches, or sets of beam bunches, being deflected, in opposite directions. M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow Pulse Generator (SPG) development M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
3. 0 Me. V MEBT Chopper (RAL FETS Scheme A) 2. 3 m Chopper 2 (slower transition) Beam dump 2 (high duty cycle) ‘CCL’ type re-buncher cavities M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
SPG development SPG beam line layout and load analysis Slow chopper electrodes Beam 16 close coupled ‘slow’ pulse generator modules M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
SPG development Prototype 8 k. V SPG euro-cassette module / Side view Axial cooling fans Air duct High voltage feed-through (output port) 0. 26 m 8 k. V push-pull MOSFET switch module Low-inductance HV damping resistors M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
SPG development SPG waveform measurement / HTS 41 -06 -GSM-CF-HFB (4 k. V) Tr =12. 0 ns Tf =10. 8 ns SPG waveforms at ± 4 k. V peak & 50 μs / div. SPG waveforms at ± 4 k. V peak & 50 ns / div. Pulse Parameter Amplitude (k. V into 50 Ohms) Transition time (ns) Duration (μs) Droop (%) Repetition frequency (MHz) Burst duration @ 1. 3 MHz Burst repetition frequency (Hz) Post pulse aberration (%) Pulse width stability (ns) Timing stability (ns over 1 hour) Burst amplitude stability (%) M. A. Clarke-Gayther FETS Requirement ± 1. 5 ~ 12. 0 0. 23 – 100 0 1. 3 0. 3 – 1. 5 ms 50 ± 5 ± 0. 1 ± 0. 5 + 10, - 5 Measured ± 4. 0 Trise ~ 12, Tfall ~ 11 0. 17 – 100 0 1. 3 1 ms 25 ≤± 5 8. 2 ns (n=1 to 2) ± 0. 3 < + 10, -5 RAL/FETS/HIPPI Compliancy Yes Yes Yes Close Yes Limited Yes Comment ± 4 k. V rated 500 pulses FWHM DC coupled Limited by cooling Damping dependent Can be corrected Over temperature Limited by power reg. CARE-07 October 30 th 2007
SPG development SPG / Summary Measured performance parameters indicate that the design is generally compliant with the RAL specification at a burst repetition frequency (BRF) of 25 Hz. Further upgrades to power supplies and cooling should allow testing at the full BRF of 50 Hz. Measurements show that for positive polarity pulses, there is a step change in the trigger to output pulse delay time between the first pulse in the burst and subsequent pulses, and that the magnitude of the change in delay time between the second pulse in the burst and the subsequent 500 pulses is then less than ~ 1 ns. Although these shifts in delay time are not compliant with the required specification, they can, in principle, be corrected by a programmable compensation technique. M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development ‘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, m 0 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: L 2 Beam transit time for distance L 1: T(L 1) Pulse transit time in vacuum for distance L 2: T(L 2) Pulse transit time in dielectric for distance L 3: T(L 3) Electrode width: L 4 For the generalised slow wave structure: Maximum value for L 1 = V 1 (T 3 - T 1) / 2 Minimum Value for L 1 = L 2 (V 1/ V 2) T(L 1) = L 1/V 1 = T(L 2) + T(L 3) M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Strategy for the development of RAL slow–wave structures Ø Modify ESS 2. 5 Me. V helical and planar designs • Reduce delay to enable 3 Me. V 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 Ø Modify helical design for CERN MEBT • Shrink to fit in 95 mm ID vacuum vessel M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development RAL Helical B 1 & B 2 structures M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Preliminary test assemblies Effort during the current reporting period has been directed towards the design, manufacture, and test of three preliminary assemblies that are viewed as an essential first step on the path to the realisation of the full scale planar and helical slow-wave structures. The manufacture and test of these assemblies is expected to provide important information on the following: Ø Construction techniques. Ø NC machining and tolerances. Ø Selection of machine-able ceramics and of copper and aluminium alloys. Ø Electroplating and electro-polishing. Ø Accuracy of the 3 D high frequency design code. M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assemblies / High frequency models and measurements The RAL planar and helical electrode designs make use of machineable ceramic pillars and discs to support and align the transmission line structures. The characteristic impedance of the transmission line at the position of these supports must be carefully controlled using compensating techniques if reflections are to be minimised. Two candidate ceramic materials have been identified, ‘Shapal-M’, and BN (HBR), and an interchangeable set of coaxial test assemblies has been designed, manufactured, and tested during this reporting period. These assemblies are viewed as an essential first step on the path to the realisation of the full scale planar and helical slow-wave structures. M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development RAL Planar A 2 / Prototype M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Shapal-M version M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Measurements in the F-domain M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Measurements in the T-domain M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Coaxial test assembly / Measurements in the T-domain M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Helical B 2 / High frequency model M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Helical B 2 / High frequency model M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Helical B 2 / CAD view M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Helical structure B 2 / Short length prototype UT-390 semi-rigid coaxial delay lines M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development RAL Planar A 2 / Prototype M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development RAL Planar A 2 / Prototype M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development RAL Planar A 2 / Pre-prototype M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development RAL Planar A 2 / Pre-prototype Coaxial interface adapter Extended dielectric connector (SMA) M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Helical structure B 2 / Prototype M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Helical structure B 2 / Pre-prototype M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Helical structure B 2 / Pre-prototype Coaxial interface adapter Extended dielectric connector (SMA) M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development ‘On-axis field in x, y plane M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Slow-wave electrode development Simulation of Helical B structure in the T & F domain M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Summary Ø FPG • Meets key specifications Ø SPG • 4 k. V version looks promising Ø Slow-wave electrode designs • Planar and Helical designs now scaled to 3. 0 Me. V • 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 M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
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 k. V SPG switch module are promising. Modification of the existing 8 k. V euro-cassette design will enable the 4 k. V 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. M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
Summary EU contract number RII 3 -CT-2003 -506395 CARE-Note-2007 -002 -HIPPI WP 4: 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 M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
References M Clarke-Gayther, ‘Slow-wave chopper structures for Next Generation High Power Proton Drivers’, Proc of PAC 2007, Albuquerque, New Mexico, USA, 25 th – 29 th June, 2007, pp. 1637 -1639 M Clarke-Gayther, ‘Slow-wave electrode structures for the ESS 2. 5 Me. V fast chopper’, Proc. of PAC 2003, Portland, Oregon, USA, 12 th - 16 th May, 2003, pp. 1473 -1475 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, 26 th - 30 th June, 2006, pp. 300 -302. F Caspers, A Mostacci, S Kurennoy, ‘Fast Chopper Structure for the CERN SPL’, Proc. of EPAC 2002, Paris, France, 3 -7 June, 2002, pp. 873 -875. F Caspers, ‘Review of Fast Beam Chopping’, Proc. of LINAC 2004, Lubeck, Germany, 16 -20 August, 2004, pp. 294 -296. M. A. Clarke-Gayther RAL/FETS/HIPPI CARE-07 October 30 th 2007
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