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Accelerator and proton beam

Accelerator and proton beam. Masahito TOMIZAWA and Satoshi MIHARA. Outline. Proton Acceleration Extraction/Transport Experimental Area. Proton Acceleration. Requirements on the Proton Beam. Beam Energy and power: 8GeV, 56kW(7 m A) Bunch width and bunch-bunch spacing:~100nsec, ~1 m sec

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Accelerator and proton beam

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  1. Accelerator and proton beam Masahito TOMIZAWA and Satoshi MIHARA

  2. Outline • Proton Acceleration • Extraction/Transport • Experimental Area

  3. Proton Acceleration

  4. Requirements on the Proton Beam • Beam Energy and power: 8GeV, 56kW(7mA) • Bunch width and bunch-bunch spacing:~100nsec, ~1msec • Extinction: <10-9 • Bunched slow extraction (slow extraction w/o switching off acceleration RF cavity)

  5. Proton Acceleration • Nominal scheme • RCS: h=2 • MR:h=9 • 8 buckets filled • 1 empty bucket, used for kicker excitation • MR RF cavities are designed for this scheme • h=18 optional by removing capacitors on cavities • Need long shutdown to change the configuration 8 filled buckets out of 9 buckets

  6. RCS: h=2 with one empty bucket MR:h=9 with 5 empty buckets Bunched slow extraction Slow extraction with RF cavity ON, 210kV Proposed Scheme (I) Realization of an empty bucket in RCS by using the chopper in Linac • Simple solution • No need of hardware modification • Heavier heat load in the scraper • Possible leakage of chopped beam in empty buckets

  7. High-frequency Chopper

  8. NO EMPTY BUCKET BOTH IN RCS AND MR Space charge tune shift is half of (1) LARGE MODIFICATION OF MR RF SYSTEM IS NECESSARY Long bunch Proposed Scheme (II) & (III) • Space charge tune shift is half of (1) • Longitudinal emittance is twice of (1) • NO EMPTY BUCKET IN RCS • RCS RF system needs minor modification (low level RF)

  9. Proton Acceleration Prospect • Try scheme (I) first for an extinction study • No hardware modification is necessary • Investigate • Time structure of the proton beam • Heat load at chopper • RF voltage while extraction • Scheme (II) may be able to be tested if h=1 operation of RCS is realized for MR intensity upgrade • Check how extinction can be improved

  10. MR Simulation • Can we estimate the extinction using simulation? • Difficult… • Impossible to trace >109 particles

  11. Acceleration 160kV constant 0turn,0s,Bf=0.046 3GeV 4000turn,0.02154s,Bf=0.049 3GeV 7450turn,0.04011s,Bf=0.050 82600turn,0.4414s,Bf=0.047 482800turn,2.54086s,Bf=0.037 30GeV

  12. Extraction/Transport

  13. Extracted Beam Size • Acceptance at MR slow extraction line and transport line is 25pmmmad • Beam size shrink by adiabatic damping isSMALL in 38GeV acceleration • Nominal scenario • space charge tune shift: -0.24 (RCS), -0.2 (MR) • 144p (0.4GeV)  54p (3GeV)  35p (8GeV) 1.5 times1.5times • Strategy • Keep MR rep. rate as high as possible • reduce particle number in the bunch to suppress space charge effect • Accelerate beam with smaller emittance than nominal • This can be achieved by • reducing painting area in RCS • narrowing transport line and MR collimator apertures

  14. Possible RCS Painting and MR Operation Pattern • 0.16x1014 ppb (1/2.6 of designed value) • 144p(0.4GeV)  36p (3GeV) 15p(8GeV) • RCS tune shift -0.046 • 93p(0.4GeV)  23p (3GeV) 10p(8GeV) • RCS tune shift -0.072 • Need measurement • MR operation pattern • 8GeV extraction • 7mA, 56kW • RCS: h=1 (1 bunch) • MR: h=9 (4 bunch), 4 batch injection • Need 6 RF cavities operational • (currently 4 in operation with 1 spare)

  15. Extraction • Same with normal slow extraction • Can we keep bunch structure during slow extraction process? • Test of “normal” slow extraction at 30GeV is scheduled on 27/Jan

  16. Bunched Slow Extraction Before extraction at ESS Extracted beam at ESS • 8GeV energy • h=9, RF cavity ON, 210kV • EL=3eVs, matched ellipse 70nsec

  17. MARS Simulation Model of the ESS Uniformly distributed beam (H:80mm, V:20mm) hits the ESS wires normally

  18. Protons scattered at the ESS wires (MARS) 40cm downstream from ESS exit Scattered to circulating side Scattered to extracted side “real loss” = N(hitted p)-N(scattered p)/N real loss0.14%=1kW remaining protons ・scattered to extracted side (one pass) ・scattered to circulated side (circulate in the ring)

  19. Transport to the Target • Detailed study is not started yet • Probably COMET needs external-extinction device, like AC dipole, to improve the extinction after extraction • The transport line must be long enough (50-100m) to include necessary equipments. • R&D work is in progress by the COMET group in collaboration with the Mu2e group

  20. Status of J-PARC Accelerator • Successful acceleration to 30GeV • Preparation of slow extraction in Jan-Feb • Test of bunched slow extraction • Extinction measurement

  21. The hall itself is ready. Beam line construction is in progress 4 secondary beam lines are planned to be built 1 primary beam line in (near) future Exp. Hall 30GeV 8GeV

  22. A possible layout…

  23. Summary • J-PARC proton acceleration for COMET • Dedicated beam bunch configuration with bunched slow extraction • Scheme (I) can be tested in 2009 • Extraction/Transport • possible area layout

  24. Bunch length

  25. Internal Extinction Device AGS internal extinction test (from BNL K. Brown slide) • Stripline AC dipole at 80 kHz excites coherent vertical betatron resonance • Fast (100 ns) kickers cancel AC dipole at the bunches • Kicker duty factor is low 100 ns / 2.7ms = 4% • Concept tested in FY98 using existing AC dipole and kickers

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