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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. Principle. Same as freefall and reaching terminal velocity
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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
Principle Same as freefall and reaching terminal velocity Gravity opposing friction Muons energy loss in gas is compensated by applied electric field resulting in equilibrium energy • Need low energy ms below ionization peak • Here energy loss is a to T, the faster ms lose energy faster than slow ms (Ionization Cooling)
Cooling aim/obvious problems • In this regime dE/dx extremely large • Slow ms don’t go far before decaying d = 10 cm sqrt(T) T in eV • m+ forms Muonium • m- 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. s(Mm) dominates over e-strippingin all gases except He s small above electron binding energy, but not known. Keep T as high as possible
Results of simulations to this point Phase rotation sections Cooling cells • 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). • He gas is used form+,H2 form-. 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. Not to scale !!
Results: • Simulation of previous scheme yielded final beam emittances of • 2-6x10-11 (pm)3 • At yields of 0.001-0.003 m+/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 1.7x10-10 (pm)3
THE GOOD: Simulations include: • individual nuclear scatters • Muonium formation • m- capture in H2 & He • tracking through thin windows • initial reacceleration • Sufficiently cool muon beams • THE BAD: • Yields are somewhat low • THE UGLY: • Large amount of free charge which would screen field • Not simulated
Nevis Experiment already reported at NuFact03 R.Galea, A.Caldwell, L.Newburgh, Nucl.Instrum.Meth.A524, 27-38 (2004) arXiv: physics/0311059 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?
Assumed initial conditions • 20nm C windows • 700KeV protons • 0.04atm He TOF=T0-(Tsi-TMCP) speed Kinetic energy
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 Experiment showed that MC could reproduce data under various conditions. Simulations of Frictional Cooling is promising. Exp. Confirmation still desired. Low acceptance but thicker windows was the culprit
Frictional 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.
Si Drift detector He gas HV Cable Up to 100KV Source
Where do we get protons? • Use strong asource match range to thickness in plastic • Note E||B, but protons starting from rest Mylar Window a Source
Heating (cooling) to equilibrium… What do we expect? He 1MV/m • Vary gas pressure/density • Vary Efield strength • Vary distance • Measure energy directly • Can our MC predict equilibrium energies? .9MV/m .8MV/m .7MV/m .6MV/m
Assorted Insulating Spacers & support structures Efield coil Support structures Source holder
Status of Experiment • Cryostat & Magnet commissioned • Grid constructed & tested. Maintained 98KV in vacuum • Source & support structures constructed • Electronics & detectors available FWHM=250eV • Silicon Drift Detector gives excellent resolution • Thus far Fe55 X-rays
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 (pm)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 m beams Frictional Cooling is an exciting potential alternative for the phase space reduction of muon beams
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 m- capture cross section using calculations of Cohen • (Phys. Rev. A. Vol 62 022512-1) • Electronic energy loss treated as continuous • Difference in m+ & m- 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 m+
E B Other problems/solutions: • 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