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