Geant Simulation of Muon Cooling Rings

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Geant Simulation of Muon Cooling Rings

• Amit Klier
• University of California Riverside

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Outline

• A short reminder from Nufact03
• The RFOFO ring
• Geometry
• Software improvements
• Simulation results
• The small dipole ring
• Geometry
• Software improvements
• Some Results

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Muc_Geant

• Modified, data-driven Geant3 application for
  simulating muon cooling
• Electric fields added
• Runge-Kutta changed to include changing electric
  fields (eg RF cavities)
• Realistic magnetic fields can be read from
  external field maps

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From Nuact03
Tetra ring simulated
Rajendran Raja Nufact 03
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The RFOFO ring

• A few code changes w.r.t. Tetra
• Realistic magnetic field maps read-in (R.
  Godang, S. Bracker MC-Note 271)

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The RFOFO ring
Full Geant simulation A. Klier MC-Note 298
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The ring geometry

• 33 m circumference
• 12 cells (2.75m)
• A wedge absorber
• opening angle 110,
• pointing upwards
• 6 RF cavities
• 28.75 cm long,
• iris radius 25 cm
• flat E field in z direction
• 2 tilted solenoids
• inner/outer r 77/88 cm
• tilt angle 3
• Only for display here

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Closed orbits in a single cell
Solid line the reference orbit
200 MeV
270 MeV
227 MeV
250 MeV
250 MeV
227 MeV
E 200 MeV
E 270 MeV
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Software improvements

• ICOOL input/output format used, ecalc9 can be
  used to calculate emittance
• Use initial time of particle at entry
• Use virtual detectors

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Cooling of a muon beam
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Comparison with ICOOL
Transmission
6-D emittance
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More comparisons
Results after 10 turns
Merit factor
Trans. W/O decay Trans. With decay Merit Factor
Balbekov (MC-264) 70 56 55
ICOOL (Fernow) -- 58 66
Geant 72 57 70
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Change beam entry angle
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The small dipole ring
Weak (edge) focusing (ideally) scaling Filled
with 10 Atm. hydrogen gas _at_ 77K
Dipole field 2 T
For P?200 MeV/c, the radius should be 60 cm
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Field map (from S. Kahn)
By in a single quadrant
By at R60 cm
Return yoke
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Reference orbit

• Scale B down to 90
• closed orbit
• P171.25 MeV/c
• Rmin56.32 cm
• (x0 in virtual detectors)

Rmin
RF cavity (active region)
Virtual detector plane
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Ellipses
Stable up to y13 cm
Y plane symmetry imposed
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Acceptance of the ring
A blob
Py19 MeV/c
y8.5 cm
Px34 MeV/c
More natural decrease with no x-z plane
symmetry
x6.5 cm
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Cooling with no scattering
Xinitial6 cm
Yinitial8 cm
tinitial 1.5 ns
Xcentral0.04 cm
Ycentral0 cm
tcentral0 ns
PXinitial30 MeV/c
PYinitial17.5 MeV/c
Einitial213 MeV
PXcentral0.12 MeV/c
PYcentral0 MeV/c
Ecentral201.8 MeV
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Software improvements

• More flexibility less hard-coding, more
  external parameters
• Field map reading code used to be RFOFO-specific,
  now more general
• More RF parameters
• Cavities in small dipole ring are off-center
• So far, only perfect pillbox (or flat field..)
  cavity are simulated
• Flexibility different frequencies, gradients,
  types can be used in the same channel

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To do

• Simulate the small dipole ring with a beam
• Introduce more realistic features
• Injection
• Detectors

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Additional Slides
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Comparison with ICOOL
Transverse emittance
Longitudinal emittance