1. M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Beam Chopper Development for Next Generation High Power Proton Drivers Michael A. Clarke-Gayther RAL / FETS / HIPPI

2. M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007  Overview  Fast Pulse Generator (FPG)  Slow Pulse Generator (SPG)  Slow – wave electrode designs  Summary Outline

3. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Maurizio Vretenar (WP Coordinator) Alessandra Lombardi (WP4 Leader) Luca Bruno, Fritz Caspers Frank Gerigk, Tom Kroyer Mauro Paoluzzi Edgar 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

4. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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)

5. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Project History and Plan

6. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 A Fast Beam chopper for Next Generation Proton Drivers / Motivation  To reduce beam loss at trapping and extraction Enable ‘Hands on’ maintenance (1 Watt / m)  To support complex beam delivery schemes Enable low loss ‘switchyards’ and duty cycle control  To provide beam diagnostic function Enable ‘low risk’ accelerator development

7. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 DesignProjectPositionTypeChoppingStatus RAL ESS & FETS MEBT Slow-wave & Array Uni- directional Prototype CERNSPLMEBTSlow-wave Uni- directional Advanced prototype LANL/LBNLSNS MEBT & LEBT Slow-wave & Discrete Uni & quad Installed & tested JAERIJPARC MEBT & LEBT Cavity & Solenoid Bi & Longitudinal Installed & tested? FNAL‘X’MEBTSlow-waveUniPrototype Fast beam chopper schemes

8. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 The RAL Front-End Test Stand (FETS) Project / Key parameters

9. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 RAL ‘Fast-Slow’ two stage chopping scheme

10. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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

11. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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)

12. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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)

13. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 FETS Scheme A / Beam-line layout and GPT trajectory plots Losses: 0.1 % @ 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)

14. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Open animated GIF in Internet Explorer

15. Overview M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 KEY PARAMETERSSCHEME A ION SPECIESH- 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

16. M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Fast Pulse Generator (FPG) development

17. FPG development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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 1.7 m FPG / Front View

18. FPG development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 FPG waveform measurement

19. M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Slow Pulse Generator (SPG) development

20. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development CARE-07 October 30 th 2007 16 close coupled ‘slow’ pulse generator modules Slow chopper electrodes Beam SPG beam line layout and load analysis

21. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development CARE-07 October 30 th 2007 Prototype 8 kV SPG euro-cassette module / Side view Low-inductance HV damping resistors 8 kV push-pull MOSFET switch module High voltage feed-through (output port) Axial cooling fans Air duct 0.26 m

22. M. A. Clarke-GaytherRAL/FETS/HIPPI SPG development CARE-07 October 30 th 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. T r =12.0 ns T f =10.8 ns Pulse ParameterFETS RequirementMeasuredCompliancyComment Amplitude (kV into 50 Ohms)± 1.5± 4.0Yes± 4 kV rated Transition time (ns)~ 12.0T rise ~ 12, T fall ~ 11Yes500 pulses Duration (μs)0.23 – 1000.17 – 100YesFWHM Droop (%)00YesDC coupled Repetition frequency (MHz)1.3 Yes Burst duration @ 1.2 MHz0.3 – 1.5 ms1 msCloseScalable Burst repetition frequency (Hz)5025CloseScalable Post pulse aberration (%)± 5≤ ± 5YesAdjustable Pulse width stability (ns)± 0.18.2 ns (n=1 to 2)Limited Can be corrected Timing stability (ns over 1 hour)± 0.5± 0.3YesOver temperature Burst amplitude stability (%)+ 10, - 5< + 10, -5Yes0.4 ms burst

23. M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Slow-wave electrode development

24. M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 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) 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: ‘E-field chopping / Slow-wave electrode design

25. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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

26. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 RAL Planar A2 / Prototype

27. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 RAL Planar A2 / Prototype

28. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 RAL Planar A2 / Pre-prototype

29. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 RAL Planar A2 / Pre-prototype Coaxial interface adapter Extended dielectric connector (SMA)

30. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Helical structure B2 / Prototype UT-390 semi-rigid coaxial delay lines

31. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Helical structure B2 / Prototype

32. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Helical structure B2 / Pre-prototype

33. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Coaxial interface adapter Extended dielectric connector (SMA) Helical structure B2 / Pre-prototype

34. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 ‘On-axis field in x, y plane

35. Slow-wave electrode development M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 Simulation of Helical B structure in the T & F domain

36. Summary M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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

37. Summary M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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.

38. Summary M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 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-2003-506395CARE-Note-2007-002-HIPPI

39. References M. A. Clarke-GaytherRAL/FETS/HIPPICARE-07 October 30 th 2007 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 MeV fast chopper’, Proc. of PAC 2003, Portland, Oregon, USA, 12th - 16th 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, 26th - 30th 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.