Frictional Cooling MC Collaboration Meeting June 11-12/2003

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Frictional CoolingMC Collaboration MeetingJune
11-12/2003
Raphael Galea
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Frictional Cooling
Ionization stops, muon too slow
Nuclear scattering, excitation, charge exchange,
ionization

• Bring muons to a kinetic energy (T) where dE/dx
  increases with T
• Constant E-field applied to muons resulting in
  equilibrium energy
• Big issue how to maintain efficiency
• First studied by Kottmann et al., PSI

1/?2 from ionization
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Problems/comments

• large dE/dx _at_ low kinetic energy
• ? low average density (gas)
• Apply E ? B to get below the dE/dx peak
• m has the problem of Muonium formation
• s(Mm) dominates over e-stripping in all
  gases except He
• m- has the problem of Atomic capture
• s small below electron binding energy, but
  not known
• Slow muons dont go far before decaying
• d 10 cm sqrt(T) T in eV
• so extract sideways (E ? B )

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Trajectories in detailed simulation
Transverse motion
Motion controlled by B field
Fluctuations in energy results in emittance
Lorentz angle drift, with nuclear scattering
Final stages of muon trajectory in gas cell
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Results of simulations to this point
Phase rotation sections
Cooling cells

• He gas is used for m, H2 for m-. There is a
  nearly uniform 5T Bz field everywhere, and Ex 5
  MeV/m in gas cell region
• Electronic energy loss treated as continuous,
  individual nuclear scattering taken into account
  since these yield large angles.

• Full MARS target simulation, optimized for low
  energy muon yield 2 GeV protons on Cu/W with
  proton beam transverse to solenoids (capture low
  energy pion cloud).

Not to scale !!
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Summary of Simulations

• Incorporate scattering cross sections into the
  cooling program
• Born Approx. for Tgt2KeV
• Classical Scattering Tlt2KeV
• Include m- capture cross section using
  calculations of Cohen (Phys. Rev. A. Vol 62
  022512-1)

• Difference in m m- energy loss rates at dE/dx
  peak
• Due to extra processes charge exchange
• Barkas Effect parameterized data from Agnello et.
  al. (Phys. Rev. Lett. 74 (1995) 371)
• Only used for the electronic part of dE/dx

• Energy loss in thin windows
• For RARAF setup proton transmitted energy
  spectrum is input from SRIM, simulating protons
  through Si detector
• (J.F. Ziegler http//www.srim.org)

Cooling factors of 105-107!!!
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• Assumed initial conditions
• 20nm C windows
• 700KeV protons
• 0.04atm He

1. Punch through protons
2. Cooled protons

TOFT0-(Tsi-TMCP)
speed
Kinetic energy
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Add windows
300nm
721KeV p
Add gas
No gas/grid/windows Extract time offsets
0.06atm
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Cool protons???
MC exp
Flat constant Background
Background exponential with mgt0
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Problems/Things to investigate

• Extraction of ms through window in gas cell
• Must be very thin to pass low energy ms
• Must be reasonably gas tight
• Can we apply high electric fields in gas cell
  without breakdown (large number of free
  electrons, ions) ? Plasma generation ? screening
  of field.
• Reacceleration bunch compression for injection
  into storage ring
• The m- capture cross section depends very
  sensitively on kinetic energy falls off sharply
  for kinetic energies greater than e- binding
  energy. NO DATA simulations use theoretical
  calculation

RD with industry?
1 student 1 Postdocgroup is growing
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Lab situated at MPI-WHI in Munich
Sharper peak in Energy than peak from measuring
time.
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Future Plans

• Frictional cooling tests at MPI with 5T
  Solenoid, alpha source
• Study gas breakdown in high E,B fields
• RD on thin windows
• Beam tests with muons to measure ? capture cross
  section
• ?-H ? H? e?s
• muon initially captured in n15 orbit, then
  cascades down to n1. Transition n2?n1
  releases 2.2 KeV x-ray.

Si drift detector Developed my MPI HLL
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Conclusions

• No clear sign of cooling but this is expected
  from lack of Magnetic field geometric MCP
  acceptance alone
• The Monte Carlo simulation can provide a
  consistent picture under various experimental
  conditions
• Can use the detailed simulations to evaluate Muon
  Collider based on frictional cooling performance
  with more confidence.still want to demonstrate
  the cooling
• Work at MPI on further cooling demonstration
  experiment using an existing 5T Solenoid and
  develop the m- capture measurement

A lot of interesting work and results to come.