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Beam Chopper Development for Next Generation High Power Proton Drivers

This report provides an overview of the development of fast and slow pulse generators for high power proton beam choppers. It includes details on electrode designs, performance measurements, and plans for further development.

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Beam Chopper Development for Next Generation High Power Proton Drivers

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

  2. Outline • Overview • Fast Pulse Generator (FPG) • Slow Pulse Generator (SPG) • Slow – wave electrode designs • Summary

  3. 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

  4. The RAL Front-End Test Stand (FETS) Project / Key parameters

  5. RAL ‘Fast-Slow’ two stage chopping scheme

  6. 3.0 MeV MEBT Chopper (RAL FETS Scheme C) 3.2 m ‘CCL’ type re-buncher cavities Chopper 1 (fast transition) Chopper 2 (slower transition)

  7. FETS Scheme A / Beam-line layout and GPT trajectory plots Voltages: Chop 1: +/- 1.28 kV (20 mm gap) Chop 2: +/- 1.42 kV (18 mm gap) Losses: 0.1 % @ input to CH1, 0.3% on dump 1 0.1% on CH2, 0.3% on dump 2

  8. Fast Pulse Generator (FPG) development

  9. 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 9 x Pulse generator cards SPG / Front View

  10. SPG waveform measurement / HTS 81-06-GSM-CF-HFB

  11. Slow Pulse Generator (SPG) development

  12. SPG beam line layout and load analysis Slow chopper electrodes Beam 16 close coupled ‘slow’ pulse generator modules

  13. 8 kV SPG pre-prototype Test Set-up - 8 kV~ 5 μF LF cap.bank HVdamping resistor 8 kV push-pullMOSFETswitch + 8 kV~ 5 μF LF cap.bank + 8 kV~ 3 nF HF cap.bank - 8 kV~ 3 nF HF cap.bank Two turn load inductance ~ 50 nH Load capacitance ~ 30 pf 6 kV, 400 MHz ÷ 1000 probe Trigger input Auxiliary power supplies Cooling fan

  14. SPG waveform measurement /HTS 81-06-GSM HFB Tr =11.9 ns Tr =15.5 ns Tf =19.7 ns Tf =11.1 ns • SPG waveforms at ± 6 kV peak & 50 ns / div. • SPG waveforms at ± 6 kV peak & 50 ns / div. • SPG waveforms at ± 6 kV peak & 2.0 μs / div. • SPG waveforms at ± 6 kV peak & 50 μs / div.

  15. Measured performance parameters / HTS 81-06-GSM HFB 8kV SPG

  16. 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

  17. SPG Development Plan / October 2006 • Bench test 4 kV rated switch • Compare results with existing 8 kV rated switch • Re-formulate specification for SPG • Based on new optical design for FETS • Obtain quotes for a custom designed switch • Based on re-formulated specification for FETS

  18. BEHLKE HTS 41-06-GSM-CF-HSB (4kV) & 81-06-GSM-CF-HSB (8kV)

  19. 4kV MOSFET switch (BEHLKE HTS 41-06-GSM-CF-HSB) / Test Set-Up

  20. 4kV MOSFET switch (BEHLKE HTS 41-06-GSM-CF-HSB) / Test Set-Up

  21. SPG waveform measurement / HTS 41-06-GSM-CF-HFB (4 kV) Tr =12.0 ns Tr =11.2 ns Tf =10.8 ns Tf =10.8 ns • SPG waveforms at ± 4 kV peak & 50 ns / div. • SPG waveforms at ± 4 kV peak & 50 ns / div. • SPG waveforms at ± 4 kV peak & 2.0 μs / div. • SPG waveforms at ± 4 kV peak & 50 μs / div.

  22. Measured performance parameters / HTS 41-06-GSM-CF-HSB (4kV)

  23. Measured performance parameters / HTS 41-06-GSM-CF-HSB (4kV)

  24. Fast-Slow Chopper / FPG & SPG synchronisation / ESS Timing FPG (0.2 ms/div.) FPG (4.0 μs/div.) SPG (0.2 ms/div.) SPG (4.0 μs/div.)

  25. Fast-Slow Chopper / FPG & SPG synchronisation / ESS Timing FPG (0.2 ms/div.) FPG (4.0 μs/div.) SPG (0.2 ms/div.) SPG (4.0 μs/div.)

  26. Measured performance parameters / HTS 41-06-GSM-CF-HSB (4kV) SPG

  27. Summary / 4 kV SPG development • Transition time and transition time stability are now compliant (just) with four bunch chopping at 324 MHz. • Maximum burst duration at 50 Hz BRF will be tested with an upgraded auxiliary power supply and improved cooling. • Timing stability (jitter) will be tested when the auxiliary power supply and cooling have been upgraded. • The 4kV SPG results are encouraging – particularly the improved transition time and pulse duration stability.

  28. Slow-wave electrode development

  29. ‘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)

  30. 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

  31. ESS planar and Helical slow-wave electrode designs Planar A Helical B Helical C

  32. Planar structure A 3D cut-away 300 mm

  33. Helical structure B with L - C trimmers and adjustable delay

  34. Helical structure B1

  35. Helical structure B1 Helical structure B2

  36. Helical structure B1 Helical structure B2

  37. Helical structure B1 Helical structure B2

  38. RAL helical B / Field in x - y plane/ line integrals along z 8.0 mm radius inscribed circle

  39. ‘On-axis field in x, y plane

  40. Simulation of Helical B structure in the T & F domain

  41. RAL Planar A2 (3.0 MeV design)

  42. RAL Planar A2 (3.0 MeV design)

  43. Selection of coaxial and strip-line dielectric support material

  44. Vacuum coaxial support disc / HF Simulation

  45. Semi-rigid to vacuum coaxial transition / HF Simulation

  46. Coaxial to strip-line 90° transition / HF simulation

  47. Planar strip-line stand-off / HF simulation

  48. Planar strip-line components / HF simulation Beam aperture 180 degree bend

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