Columbia University & the Max-Planck-Institute
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Transcript of Columbia University & the Max-Planck-Institute
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Columbia University & the Max-Planck-Institute
Review & Status of Frictional Cooling
A. Caldwell, R. Galea, D. Kollar
• Principle• Simulations• Review of Nevis Experiment• Outline next experimental steps at MPI• Summary
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
PrincipleSame as freefall and reaching terminal velocity
Gravity opposing frictionMuons energy loss in gas is compensated by applied electric field resulting in equilibrium energy
(Ionization Cooling)
• Need low energy s below ionization peak• Here energy loss is to T, the faster s lose energy faster than slow s
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Cooling aim/obvious problems• In this regime dE/dx extremely large• Slow s don’t go far before decaying d = 10 cm sqrt(T) T in eV • + forms Muonium • - is captued by Atom
• Low average density (gas)
• Apply EB to get below the dE/dx peak• Make Gas cell long as you want but transverse dimension (extraction) small.
dominates over e-strippingin all gases except He
small above electron binding energy, but not known. Keep T as high as possible
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
rdx
dTBvEqF
)(
Oscillations around equilibrium limits final emittance
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Cooling cells
Phase rotation sections
Not to scale !!
He gas is used for +, H2 for -. There is a nearly uniform 5T Bz field everywhere, and Ex =5 MV/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 with proton beam transverse to solenoids (capture low energy pion cloud).
Results of simulations to this point
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Results:Baseline parameters for high energy muon colliders. From “Status of Muon ColliderResearch and Development and Future Plans,” Muon Collider Collaboration, C. M.Ankenbrandt et al., Phys. Rev. ST Accel. Beams 2, 081001 (1999).
COM energy (TeV) 0.4 3.0p energy (GeV) 16 16p’s/bunch 2.5 1013 2.5 1013
Bunches/fill 4 4Rep. rate (Hz) 15 15p power (MW) 4 4/ bunch 2 1012 2 1012
power (MW) 4 28Wall power (MW) 120 204Collider circum. (m) 1000 6000Ave bending field (T) 4.7 5.2rms p/p (%) 0.14 0.16
6D (m)3 1.7 10 10 1.7 10 10
rms n ( mm mrad) 50 50
* (cm) 2.6 0.3
z (cm) 2.6 0.3
r spot (m) 2.6 3.2 IP (mrad) 1.0 1.1Tune shift 0.044 0.044nturns (effective) 700 785
Luminosity (cm 2 s 1) 1033 7 1034
1.7x10-10 (m)3
• Simulation of previous scheme yielded final beam emittances of 2-6x10-11 (m)3
At yields of 0.001-0.003 +/GeV proton.
• Yield could be better yet emittance is better than ”required”• Cooler beams
• smaller beam elements• less background• lower potential radiation hazard from neutrinos
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
THE GOOD: Simulations include: • individual nuclear scatters• Muonium formation• - capture in H2 & He• tracking through thin windows• initial reaccelerationSufficiently cool muon beamsSufficiently cool muon beams
THE BAD:• Yields are somewhat low
THE UGLY:• Large amount of free charge which would screen field• Not simulated
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
RAdiological Research Accelerator Facility•Perform TOF measurements with
protons•2 detectors START/STOP•Thin entrance/exit windows for a gas cell•Some density of He gas•Electric field to establish equilibrium energy•NO B field so low acceptance
Look for a bunching in time •Can we cool protons?
Nevis Experiment already reported at NuFact03R.Galea, A.Caldwell, L.Newburgh, Nucl.Instrum.Meth.A524, 27-38 (2004)arXiv: physics/0311059
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
4 MeV p
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Assumed initial conditions•20nm C windows•700KeV protons•0.04atm He
TOF=T0-(Tsi-TMCP) speed Kinetic energy
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Results of RARAF experiment
• Various energies/gas pressures/electric field strengths indicated no cooled protons• Lines are fits to MC & main peaks correspond to protons above the ionization peak
Low acceptance but thicker windows was the culprit
Experiment showed that MC could reproduce data under various conditions. Simulations of Frictional Cooling is promising. Exp. Confirmation still desired.
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Frictional Cooling Demonstration at MPI MunichFrictional Cooling Demonstration at MPI Munich
• Repeat demonstration experiment with protons with IMPROVEMENTS:• No windows• 5T Superconducting Solenoid for high acceptance• Silicon detector to measure energy directly
Cryostat housing 5T solenoid.
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
HV Cable
Si Drift detector
He gas
Source
BE
,
Up to 100KV
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Source
Mylar Window
Where do we get protons?Where do we get protons?• Use strong source match range to thickness in plastic• Note E||B, but protons starting from rest
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Heating (cooling) to equilibrium…Heating (cooling) to equilibrium…What do we expect?What do we expect?
He
1MV/m
.9MV/m
.8MV/m
.7MV/m
.6MV/m
• Vary gas pressure/density• Vary Efield strength• Vary distance • Measure energy directly• Can our MC predict equilibrium energies?
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Efield coilSupport structures
Source holder
Assorted Insulating Spacers & supportstructures
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Status of ExperimentStatus of Experiment
FWHM=250eV
• Silicon Drift Detector gives excellent resolution• Thus far Fe55 X-rays
• Cryostat & Magnet commissioned• Grid constructed & tested. Maintained 98KV in vacuum• Source & support structures constructed• Electronics & detectors available
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Summary• Frictional Cooling is being persued as a potential cooling method intended for Muon Colliders• Simulations of mostly ideal circumstances show that the 6D emittance benchmark of 1.7x10-10 (m)3 can be achieved & surpassed• Simulations have been supported by data from Nevis Experiment & will be tested further at the Frictional Cooling Demonstration to take place at MPI Munich• Future investigations are also on the program:
• R&D into thin window or potential windowless systems• Studies of gasbreakdown in high E,B fields• Capture cross section measurements at beams
Frictional Cooling is an exciting potential Frictional Cooling is an exciting potential alternative for the phase space reduction of alternative for the phase space reduction of muon beamsmuon beams
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Something about simulations• Individual nuclear scatters are simulated – crucial in determining final phase space, survival probability.
• Incorporate scattering cross sections into the cooling program
• Include - capture cross section using calculations of Cohen (Phys. Rev. A. Vol 62 022512-1)
• Electronic energy loss treated as continuous
• Difference in + & - energy loss rates at dE/dx peak (parameterized data from Agnello et. al. (Phys. Rev. Lett. 74 (1995) 371))
• Partly due to charge exchange for +
NuFact04 July26-August 1, 2004Osaka University, Osaka, Japan
Other problems/solutions:
B
E
• Thin windows important issue – Nevis Experiment• Breakdown in Gas Paschen Curves• Large amount of free charge which would screen field
• In ExB field particle undergoes cycloid motion limiting max kinetic energy a 2mE/B. Choose E & B appropriately to keep energy below ionization energy to prevent multiplication