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Geant4 Simulations of the MICE Beamline

Geant4 Simulations of the MICE Beamline. Tom Roberts Illinois Institute of Technology June13, 2003. 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.

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Geant4 Simulations of the MICE Beamline

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  1. Geant4 Simulations of the MICE Beamline Tom Roberts Illinois Institute of Technology June13, 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.

  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 Zvia symmetry Pole Solution Region Solution Region Solution Region Pole

  4. RAL Type I bending Magnet Model

  5. Every element has a name micebeam.in (Input to g4beamline) A solenoid is a coil plus a current The coil has a sharable map coil Decay innerRadius=200.0 outerRadius=250.0 length=5000.0 material=Cu solenoid DecayS coilName=Decay current=47.94 color=1,0,0 tubs SolenoidBody innerRadius=250 outerRadius=1000 length=5000 kill=1 group DecaySolenoid length=5000 place DecayS z=0 place SolenoidBody z=0 endgroup idealquad default ironRadius=381 ironLength=1104.9 kill=1 idealquad 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,.6 idealquad 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=3000 place Q2 z=4400 place Q3 z=5800 place B1 z=7855.8 rotation=Y30 x=250 corner B1c z=8000 rotation=Y60 place DecaySolenoid z=12200 place B2 z=16135 rotation=Y15.8 x=175 corner B2c z=16185 rotation=Y31.7 place MICEdiffuser1 z=18840 Group Elements together “tubs” is Geant4-speak for a tube or cylinder Color is R,G,B Omitted=invisible Kill=1 makes a Perfect Shield. A detector generates an NTuple A corner in the centerline Y60 is a 60° rotation around Y; Multiple rotations: Y60,Z45,X90 The beam and physics specifications are omitted for clarity, as is other basic stuff.

  6. MICE Beamline layout

  7. Colors 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 Pictures of Simulated Tracks • 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).

  8. Good Muon

  9. π+ μ+  e+ Positrons are quite rare.

  10. Pion There are also a gazillion protons.

  11. There are many ways for muons to miss

  12. There are many ways for muons to miss

  13. There are many ways for muons to miss

  14. But some are just lucky

  15. Pions – Beam Loss position along Centerline

  16. Pions at the MICE Z Position

  17. Muons at the MICE Z Position

  18. Protons at the MICE Z Position

  19. Pion Momentum at the MICE Z position

  20. Muon Momentum at the MICE Z Position

  21. Proton Momentum at the MICE Z Position Scale is different – this is quite similar to the π+ momentum distribution.

  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.

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