Simulation study of the J-PARC
primary proton beamline
OutlineIntroduction
Simulation setup
Estimation of beam loss and design parameters
Collimators
Radiation shield
Summary1

Introduction - J-PARC Neutrino beamline Proton Beam Power at J-PARC Æ ~100 times larger than K2K(750 kW)Beam loss induces large radiation dose.
(Total Beam loss limit : 1W/m in Arc)

The Arc Section consists of super-conducting magnets.
Protect the super-conducting magnets from quenching(Line loss limit : 10W/1magnet)
PQ2B

50GeV ring

PQ5PH3PQ4B

PQ4A

PV1 PQ3B

PQ3APD2

PQ1

PQ2A
PD1bend1.92 deg.

PH2

PH1

1.92 deg. bend

PV2

ニュートリノ・ビームライン

Preparation section ~50m
Conventional magnet

Arc section ~150m

FQ2B

FQ2A

FH1

FQ1Super-conducting magnet

It is very important to reduce thebeam loss in the arc section indesigning the proton beam line.

FH2

FQ3A

Final Focusing section ~40m
Conventional magnet

FQ3B
FQ4
FV2

Collimators and Shield in Preparation Section
Beam core: ε =6 [π∗mm*mrad] , dP/P = 0.3%
AcceptancePreparation section : ε =60 [π∗mm*mrad]
Arc section : larger than preparation section
To controll the energy deposit in the arc section, the design ofthe preparation section is important.
We have varied the design parameters, andestimated the beam loss in the arc section.
Components we studied with simulation

Preparation section

BeamCollimators
Radiation shield at the exit of the preparation section
3

Simulation Setup with Geant4
Preparation section
Beam halo parameter

ArcEbeam = 50 GeV
dP/P = 2.0%
ε = 0~200 [π∗mm*mrad](uniform distribution in phase space)x’t[nihor]pebmut[Misopdyrg]nVeFinal Focus
x

Inject beam halo, estimate
beam loss in the arc section.

4Simulated beam loss at each component

energy deposit [MeV]

Preparation section
Total beam loss Æ750W
Total loss deposited incomponents
Æ 508W
101010Arc

FF

3.7W

96

3

1

050

150
100orbit length [m]200250t[Misopdyrg]nVet[nihor]pebmu

Total beam loss in preparation section
is assumed 750W (0.1%).
On this assumption, energy deposit in each component werenormalized.
5Collimator design

thicknesslengthgap
gap width

To protect the Arc magnets frombeam loss, collimators in
preparation section scrape off thebeam halo.

beam

Current design
Thickness : 50 cm
Length : 1.45 ~ 3.0 m
Gap height : 3.1 ~ 9.5 cm
Gap width : 6.4 ~ 12.1 cm

Fills up as much drift space aspossible.
These gap sizes are designed toaccept particles in ε = 60 [π *mm * mrad] .
Æ Very large collimators (very conservative)

6Collimator design - Thickness of collimators We checked whether we can make collimators smaller
without increase of the beam loss in super-conducting magnets
in arc section and conventional magnets in preparation section.

420Arc Total
FeW

320

Energy Deposit [W]Energy Deposit [W]Magnets around thecollimators at thepreparation section

10 20 30 40 50 60
Collimator Thickness [cm]

PQ3PV2PQ4PH3PQ5Fe Collimator

1000

10 20 30 40 50 60
Collimator Thickness [cm]Calculation result indicates that 5cm is thick enough.

7Collimator design - Length -nominalArc Total
50cm

654321010cmEnergy Deposit [W]

We changed the length of collimators.

Collimator Length

Making collimators shorter increases energy depositin the arc section.
Length of the collimators must be long.

8Radiation Shield at the exit of preparation section
Tunnel wall
Shieldshowers
Beamline~3 mArc

Preparation section

In order to protect the superconducting magnets from shower
particles generated in preparation
section, radiation shield can beplaced at the exit of the preparation
section.
Assumed shield size :1m thick, 3m wide (tunnel filler
like illustrated in the left figure)material of shield :concrete, iron or tungsten

1m9Radiation Shield at the exit of preparation section
The inner diameter of the shield :100mm
result is nearly identical with those without shield.

Energy deposit [W]smaller(50 or 60mm)
15Concrete

the energy deposit in the arc section increased, due
to the shower particles generated at the shield.
FeW

Without Shield
15Arc Total@ Arc 1st CF magnet

1010550406080 100 120
Shield gap size [mm]0406080 100 120
Shield gap size [mm]The current simulation result does not favor the radiation shieldat the exit of preparation section.

10Summary
We have carried out the J-PARC proton beamline simulation studies.
We estimated the beam loss, and studied the design forcollimators and radiation shield.
Collimator
Thickness : 5cm is good enough.
length : > 1m needed.
Radiation shield at the exit of preparation section
The current simulation study does not favor.

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