june 13, 20031 geant4 simulations of the mice beamline tom roberts illinois institute of technology...
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![Page 1: June 13, 20031 Geant4 Simulations of the MICE Beamline Tom Roberts Illinois Institute of Technology June13, 2003](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d485503460f94a2337e/html5/thumbnails/1.jpg)
June 13, 2003 1
Geant4 Simulations of the MICE Beamline
Tom Roberts
Illinois Institute of Technology
June13, 2003
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June 13, 2003 2
Introducing the g4beamline Program• A general tool for simulating beamlines, using Geant4 5.1p1.• All problem-specific aspects of the simulation are given in a
simple ASCII file.• The basic idea is to define elements, and then to place them
into the system (perhaps multiple times).• Centerline coordinates can be used, simplifying layout for
beamline-like configurations.– Centerline coordinates are piecewise-straight, with the z axis down
the nominal centerline of the beamline.– The centerline coordinates {x,y,z} rotate at a corner (bending
magnet), as do all elements placed after the corner.
• By default, objects are simply lined up along the centerline; specific locations and rotations can also be given.
• The complexity of the description matches the complexity of the problem.
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June 13, 2003 3
The MICE Beamline Simulation• Decay Solenoid:
– Accurate magnetic map computed via infinitely-thin sheets– Map parameters (# sheets,nR,nZ,dR,dZ,length) are determined
automatically, given the required accuracy (0.0002 relative accuracy used)
• Quadrupole Magnets:– Perfect and constant block fields used.– No fringe fields.
• Bending Magnets:– Fringe field computation - Laplace’s Equation for magnetic
potential– Assume infinitely-wide– Computation done using Excel,
1 mm grid– Solution extended in Y and Z
via symmetry
Pole
Pole
Solution RegionSolution RegionSolution Region
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June 13, 2003 4
RAL Type I bending Magnet Model
Bend Type 1 (pole half-length=457, Eff-half-length=519)
B fields
-0.2000
0.0000
0.2000
0.4000
0.6000
0.8000
1.0000
1.2000
0 200 400 600 800 1000
By on AxisBz Halfway up
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micebeam.in (Input to g4beamline)coil Decay innerRadius=200.0 outerRadius=250.0 length=5000.0 material=Cu solenoid DecayS coilName=Decay current=47.94 color=1,0,0tubs SolenoidBody innerRadius=250 outerRadius=1000 length=5000 kill=1group DecaySolenoid length=5000
place DecayS z=0place SolenoidBody z=0
endgroup
idealquad default ironRadius=381 ironLength=1104.9 kill=1idealquad Q1 fieldLength=863.6 fieldRadius=101.6 gradient=2.0 ironColor=0,.6,0 idealquad Q2 fieldLength=863.6 fieldRadius=101.6 gradient=-3.0 ironColor=0,0,.6idealquad Q3 fieldLength=863.6 fieldRadius=101.6 gradient=0.8 ironColor=0,.6,0
mappedmagnet B1 mapname=RALBend1 Bfield=-0.9646 \fieldWidth=660.4 fieldHeight=152 fieldLength=2000 fieldColor='' \ironLength=1397 ironHeight=1320 ironWidth=1981 ironColor=1,1,0 kill=1
mappedmagnet B2 mapname=RALBend1 Bfield=-0.3512 \fieldWidth=660.4 fieldHeight=152 fieldLength=2000 fieldColor='' \ironLength=1397 ironHeight=1320 ironWidth=1981 ironColor=1,1,0 kill=1
detector MICEdiffuser1 radius=250 length=1.0 color=0,1,1
place Q1 z=3000place Q2 z=4400place Q3 z=5800place B1 z=7855.8 rotation=Y30 x=250corner B1c z=8000 rotation=Y60place DecaySolenoid z=12200place B2 z=16135 rotation=Y15.8 x=175corner B2c z=16185 rotation=Y31.7place MICEdiffuser1 z=18840
Group Elements together
A corner in the centerlineY60 is a 60° rotation around Y;
Multiple rotations: Y60,Z45,X90
Kill=1 makes a Perfect Shield.
“tubs” is Geant4-speak for atube or cylinder
A detector generates an NTuple
The beam and physicsspecifications are omitted for clarity, asis other basic stuff.
Every elementhas a name
Color is R,G,BOmitted=invisible
A solenoid is a coil plus a currentThe coil has a sharable map
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June 13, 2003 6
MICE Beamline layout
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June 13, 2003 7
Pictures of Simulated TracksColors of Tracks:
Green pi+
Blue mu+
White e+
Other particles are killed.
Colors of Objects:
Green Focusing Quad
Blue Defocusing Quad
Yellow Bending Magnet
Red Decay Solenoid
White Wide detector at
MICE Z Position
• The target is at the lower left, with protons not shown – if they were shown they would head 25 degrees down to the lower right.
• The detector at MICE diffuser1 is much larger than the experimental acceptance, so I can see what’s out there.
• For quads and the solenoid, only the ends are shown.• These pictures are 2-d plan views (not 3-d as the previous picture).
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June 13, 2003 8
Good Muon
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June 13, 2003 9
π+ μ+ e+
Positrons are quite rare.
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June 13, 2003 10
Pion
There are also a gazillion protons.
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June 13, 2003 11
There are many ways for muons to miss
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June 13, 2003 12
There are many ways for muons to miss
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June 13, 2003 13
There are many ways for muons to miss
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June 13, 2003 14
But some are just lucky
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June 13, 2003 15
Pions – Beam Loss position along Centerline
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June 13, 2003 16
Pions at the MICE Z Position
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June 13, 2003 17
Muons at the MICE Z Position
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June 13, 2003 18
Protons at the MICE Z Position
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June 13, 2003 19
Pion Momentum at the MICE Z position
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June 13, 2003 20
Muon Momentum at the MICE Z Position
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June 13, 2003 21
Proton Momentum at the MICE Z Position
Scale is different – this is quite similar to the π+ momentum distribution.
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June 13, 2003 22
Conclusions
• Visualization is essential to verify the layout is correct.
• g4beamline is a flexible and useful tool for simulations like this.
• The MICE detector will have significant backgrounds from the beamline – not to mention strays that cannot be accurately modeled, and of course Cosmic Rays.
• We need to compute normalized fluxes for protons, pions, and muons.
• Diffuser1 is clearly not needed to “spread out the beam”; Diffuser2 is still required to break the angle-position correlation.