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M m on Cooling RINGBERG 21-25 July, 2003

M m on Cooling RINGBERG 21-25 July, 2003. Studies at Columbia University/Nevis Labs & MPI Raphael Galea, Allen Caldwell. How to reduce beam Emmittance by 10 6 ?  6D,N = 1.7 10 -10 (  m) 3. Why Muons, why Muon Collider? Muon Cooling, Ionization or Frictional Cooling

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M m on Cooling RINGBERG 21-25 July, 2003

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  1. Mmon CoolingRINGBERG21-25 July, 2003 Studies at Columbia University/Nevis Labs & MPI Raphael Galea, Allen Caldwell How to reduce beam Emmittance by 106? 6D,N = 1.7 10-10 (m)3 • Why Muons, why Muon Collider? • Muon Cooling, Ionization or Frictional Cooling • Frictional Cooling with protons • Conclusions and future work

  2. Why a Muon Collider ? No synchrotron radiation problem (cf electron) P a (E/m)4 Can build a high energy circular accelerator. Collide point particles rather than complex objects P P Ringberg Workshop 21-25 July, 2003

  3. Dimensions of Some Colliders discussed Ringberg Workshop 21-25 July, 2003

  4. Why Cooling? • All Colliding beams have some cooling to reduce the large phase space of initial beam • RADIATIVE • lose the hot particles • STOCHASTIC • sample particles passing cooling system • correct to mean position • ELECTRON • principle of heat exchanger Ringberg Workshop 21-25 July, 2003

  5. From target, stored  = 40000 ee Ringberg Workshop 21-25 July, 2003

  6. HIGH ENERGY MUON COLLIDER PARAMETERS Ringberg Workshop 21-25 July, 2003

  7. p’s in red m’s in green Drift region for  decay  30 m P beam (few MW) Solenoidal Magnets: few T … 20 T Target Simplified emittance estimate: At end of drift, rms x,y,z approx 0.05,0.05,10 m Px,Py,Pz approx 50,50,100 MeV/c Normalized 6D emittance is product divided by (mmc)3 drift6D,N 1.7 10-4 (m)3 Emittance needed for Muon Collider collider6D,N 1.7 10-10(m)3 This reduction of 6 orders of magnitude must be done with reasonable efficiency ! Ringberg Workshop 21-25 July, 2003

  8. Some Difficulties • Muons decay, so are not readily available – need multi MW source. Large starting cost. • Muons decay, so time available for cooling, bunching, acceleration is very limited. Need to develop new techniques, technologies. • Large experimental backgrounds from muon decays (for a collider). Not the usual clean electron collider environment. • High energy colliders with high muon flux will face critical limitation from neutrino induced radiation. Ringberg Workshop 21-25 July, 2003

  9. Muon Cooling Muon Cooling is the signature challenge of a Muon Collider • Cooler beams would allow fewer muons for a given luminosity, thereby • Reducing the experimental background • Reducing the radiation from muon decays • Allowing for smaller apertures in machine elements, and so driving the cost down Ringberg Workshop 21-25 July, 2003

  10. Cooling Ideas : Ionization Cooling RF  beam B Gas cell Ionization cooling (Skrinsky, Neuffer, Palmer, …): muons are maintained at ca. 200 MeV. Transverse cooling of order x20 seems feasible (see -factory feasibility studies 1-2). Longitudinal cooling not solved. Ringberg Workshop 21-25 July, 2003

  11. Longitudinal Cooling via Emittance Exchange Transform longitudinal phase space into transverse (know how to cool transverse) Wedge shaped absorber Bent solenoid produces dispersion Ringberg Workshop 21-25 July, 2003

  12. ‘Balbekov Ring’ There are significant developments in achieving 6D phase space via ionization cooling (R. Palmer, MUTAC03), but still far from 106 cooling factor. Ringberg Workshop 21-25 July, 2003

  13. Ionization stops, muon too slow Frictional Cooling 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 Ringberg Workshop 21-25 July, 2003

  14. Problems/comments: • large dE/dx @ 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-strippingin all gases except He • m-has the problem of Atomic capture s small below electron binding energy, but not known • Slow muons don’t go far before decaying d = 10 cm sqrt(T) T in eV so extract sideways (E  B ) Ringberg Workshop 21-25 July, 2003

  15. 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 Ringberg Workshop 21-25 July, 2003

  16. 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 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. Not to scale !! Ringberg Workshop 21-25 July, 2003

  17. Yields & Emittance Results as of NUFACT02 Look at muons coming out of 11m cooling cell region after initial reacceleration. Yield: approx 0.002  per 2GeV proton after cooling cell. Need to improve yield by factor 3 or more. Emittance: rms x = 0.015 m y = 0.036 m z = 30 m ( actually ct) Px = 0.18 MeV Py = 0.18 MeV Pz = 4.0 MeV 6D,N = 5.7 10-11 (m)3 6D,N = 1.7 10-10 (m )3 Ringberg Workshop 21-25 July, 2003

  18. 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? Ringberg Workshop 21-25 July, 2003

  19.  4 MeV p Ringberg Workshop 21-25 July, 2003

  20. Contains O(10-100nm) window Accelerating grid Si detector To MCP Proton beam Gas cell Ringberg Workshop 21-25 July, 2003 Vacuum chamber

  21. Assumed initial conditions • 20nm C windows • 700KeV protons • 0.04atm He TOF=T0-(Tsi-TMCP) speed Kinetic energy

  22. Summary of Simulations • Incorporate scattering cross sections into the cooling program • Born Approx. for T>2KeV • Classical Scattering T<2KeV • 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 Effectparameterized 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) Ringberg Workshop 21-25 July, 2003

  23. Cool protons??? MC exp Flat constant Background Background exponential with m>0 Ringberg Workshop 21-25 July, 2003

  24. 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. Ringberg Workshop 21-25 July, 2003

  25. Lab situated at MPI-WHI in Munich Ringberg Workshop 21-25 July, 2003

  26. 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 • +… Ringberg Workshop 21-25 July, 2003

  27. Future Plans • Frictional cooling tests at MPI with 5T Solenoid, alpha source • Study gas breakdown in high E,B fields • R&D on thin windows • Beam tests with muons to measure  capture cross section • -+H  H+ e+’s • muon initially captured in n=15 orbit, then cascades down to n=1. Transition n=2n=1 releases 2.2 KeV x-ray. Si drift detector Developed by MPI HLL Ringberg Workshop 21-25 July, 2003

  28. Summary of Frictional Cooling • Works below the Ionization Peak • Detailed simulations • Cooling factors O(106) or more? • Still unanswered questions being worked on but early results are encouraging. Proton cooling test Y(cm) Kinetic Energy(KeV) Time(ns) X(cm)

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