1. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Beam Chopper Development for Next Generation High Power Proton Drivers Michael A. Clarke-Gayther RAL / FETS / HIPPI

2. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008  Overview  Fast Pulse Generator (FPG)  Slow Pulse Generator (SPG)  Slow – wave electrode designs  Summary Outline

3. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Maurizio Vretenar (HIPPI WP coordinator) Alessandra Lombardi (WP4 Coordinator) 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. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 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)

5. Overview M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Project History and Plan

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

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

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

9. Overview M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 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 & Induction Bi & Longitudinal Installed & tested? FNAL‘X’MEBTSlow-waveUniPrototype Fast beam chopper schemes

10. Overview M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 The RAL Front-End Test Stand (FETS) Project / Key parameters

11. Overview M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 RAL ‘Fast-Slow’ two stage chopping scheme

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

13. Overview M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 3.0 MeV MEBT Chopper (RAL FETS Scheme A) Chopper 1 (fast transition) ‘CCL’ type re-buncher cavities 2.4 m Beam dump 1 (low duty cycle)

14. Overview M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 3.0 MeV MEBT Chopper (RAL FETS Scheme A) Chopper 2 (slower transition) ‘CCL’ type re-buncher cavities 2.4 m Beam dump 2 (high duty cycle)

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

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

17. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Open animated GIF in Internet Exploreranimated

18. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Fast Pulse Generator (FPG) development

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

20. FPG development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 FPG waveform measurement

21. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Slow Pulse Generator (SPG) development

22. M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development UK-NF 16 th September 2008 16 close coupled ‘slow’ pulse generator modules Slow chopper electrodes Beam SPG beam line layout and load analysis

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

24. M. A. Clarke-Gayther RAL/FETS/HIPPI SPG development UK-NF 16 th September 2008 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 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 @ 1.3 MHz0.3 – 1.5 ms1 msCloseLimited by cooling Burst repetition frequency (Hz)5025CloseLimited by cooling Post pulse aberration (%)± 5≤ ± 5YesDamping dependent 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, -5YesLimited by power reg. T r =11.3 ns T f =11.3 ns

25. M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Slow-wave electrode development

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

27. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 ‘On-axis field in x, y plane

28. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Preliminary test assemblies  Coaxial  Helical  Planar

29. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 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.

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

31. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Coaxial test assembly / Shapal-M version

32. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Helical test assembly

33. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Helical B2 / Short length prototype UT-390 semi-rigid coaxial delay lines

34. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 Helical B2 / CAD view

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

36. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 RAL Planar / Short length prototype

37. Slow-wave electrode development M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 RAL Planar / Short length prototype

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

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

40. References M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 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-2003-506395CARE-Report-08-016-HIPPI

41. References M. A. Clarke-Gayther RAL/FETS/HIPPI UK-NF 16 th September 2008 M Clarke-Gayther, ‘The development of a fast beam chopper for next generation high power proton drivers’, Proc. of EPAC 2008, Genoa, Italy, 23 rd – 27 th 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, 25 th – 29 th 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, 26 th - 30 th 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, 16 th – 20 th May, 2005, pp. 3637-3639 M Clarke-Gayther, ‘A fast beam chopper for next generation proton drivers’, Proc. of EPAC 2004, Lucerne, Switzerland, 5 th – 9 th 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, 12 th - 16 th May, 2003, pp. 1473-1475 F Caspers, ‘Review of Fast Beam Chopping’, Proc. of LINAC 2004, Lubeck, Germany, 16 th – 20 th August, 2004, pp. 294-296. F Caspers, A Mostacci, S Kurennoy, ‘Fast Chopper Structure for the CERN SPL’, Proc. of EPAC 2002, Paris, France, 3 rd – 7 th June, 2002, pp. 873-875.