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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 - PowerPoint PPT Presentation
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Masahito TOMIZAWA and Satoshi MIHARA
Accelerator and proton beam
Outline
2
Proton Acceleration
Extraction/Transport
Experimental Area
Proton Acceleration
Requirements on the Proton Beam Beam Energy and power: 8GeV, 56kW(7A) Bunch width and bunch-bunch spacing:~100nsec, ~1sec Extinction: <10-9
Bunched slow extraction (slow extraction w/o switching off acceleration RF cavity)
Proton AccelerationNominal scheme
RCS: h=2MR:h=9
8 buckets filled1 empty bucket, used
for kicker excitation
MR RF cavities are designed for this schemeh=18 optional by
removing capacitors on cavities
Need long shutdown to change the configuration
8 filled buckets out of 9 buckets
Proposed Scheme (I) RCS: h=2 with one empty
bucket MR:h=9 with 5 empty
buckets Bunched slow extraction
Slow extraction with RF cavity ON, 210kV
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
•Simple solution
•No need of hardware modification
•Heavier heat load in the scraper
•Possible leakage of chopped beam in empty buckets
High-frequency Chopper
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)
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
Proton Acceleration ProspectTry scheme (I) first for an extinction
studyNo hardware modification is necessaryInvestigate
Time structure of the proton beamHeat load at chopperRF voltage while extraction
Scheme (II) may be able to be tested if h=1 operation of RCS is realized for MR intensity upgradeCheck how extinction can be improved
MR Simulation
11
Can we estimate the extinction using simulation?Difficult…Impossible to trace >109 particles
0turn,0s,Bf=0.0463GeV
82600turn,0.4414s,Bf=0.047
7450turn,0.04011s,Bf=0.050 4000turn,0.02154s,Bf=0.0493GeV
Acceleration 160kV constant
482800turn,2.54086s,Bf=0.03730GeV
Extraction/Transport
Extracted Beam Size Acceptance at MR slow extraction line and transport line is
25mmmad Beam size shrink by adiabatic damping is SMALL in 38GeV
acceleration
Nominal scenario space charge tune shift: -0.24 (RCS), -0.2 (MR) 144 (0.4GeV) 54 (3GeV) 35 (8GeV) 1.5 times 1.5times
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
Possible RCS Painting and MR Operation Pattern
0.16x1014 ppb (1/2.6 of designed value) 144(0.4GeV) 36 (3GeV) 15(8GeV)
RCS tune shift -0.046 93(0.4GeV) 23 (3GeV) 10(8GeV)
RCS tune shift -0.072Need measurement
MR operation pattern8GeV extraction7A, 56kWRCS: h=1 (1 bunch)MR: h=9 (4 bunch), 4 batch injectionNeed 6 RF cavities operational
(currently 4 in operation with 1 spare)
ExtractionSame with normal slow extractionCan we keep bunch structure during slow
extraction process?Test of “normal” slow extraction at 30GeV is
scheduled on 27/Jan
Bunched Slow Extraction
8GeV energy h=9, RF cavity ON, 210kV EL=3eVs, matched ellipse
Before extraction at ESS Extracted beam at ESS
70nsec
Uniformly distributed beam(H:80m, V:20mm)hits the ESS wires normally
MARS Simulation Model of the ESS
“real loss” = N(hitted p)-N(scattered p)/N real loss 0.14%=1kW remaining protons ・ scattered to extracted side (one pass) ・ scattered to circulated side (circulate
in the ring)0
50010001500200025003000350040004500
-6 -5.9 -5.8 -5.7 -5.6 -5.5 -5.4 -5.3 -5.2 -5.1 -5
Protons scattered at the ESS wires (MARS)
Scattered to extracted side
40cm downstream from ESS exit
Scattered to circulating side
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
Status of J-PARC Accelerator
21
Successful acceleration to 30GeV
Preparation of slow extraction in Jan-FebTest of bunched slow
extractionExtinction
measurement
Exp. Hall
22
The hall itself is ready.Beam line construction
is in progress4 secondary beam lines
are planned to be built1 primary beam line in
(near) future
30GeV8GeV
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
Bunch length
Stripline AC dipole at 80 kHz excites coherent vertical betatron resonance
Fast (100 ns) kickers cancel AC dipole at the bunchesKicker duty factor is low 100 ns / 2.7s = 4% Concept tested in FY98 using existing AC dipole and kickers
AGS internal extinction test (from BNL K. Brown slide)
Internal Extinction Device