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Mmon Cooling RINGBERG 21-25 July, 2003 Studies at Columbia University/Nevis Labs & MPI Raphael Galea, Allen Caldwell • Why Muons, why Muon Collider? • Muon Cooling, Ionization or Frictional Cooling • Frictional Cooling with protons • Conclusions and future work How to reduce beam Emmittance by 106? 6D,N = 1.7 10-10 (m)3 Why a Muon Collider ? No synchrotron radiation problem (cf electron) P a (E/m)4 Can build a high energy circular accelerator. P R. Galea P Ringberg Workshop 21-25 July, 2003 Collide point particles rather than complex objects Dimensions of Some Colliders discussed R. Galea Ringberg Workshop 21-25 July, 2003 Why Cooling? • All Colliding beams have some cooling to reduce the large phase space of initial beam STOCHASTIC • sample particles ELECTRON • principle of RADIATIVE • lose the hot passing cooling system • correct to mean position heat exchanger particles R. Galea Ringberg Workshop 21-25 July, 2003 Physics at a Muon Collider Muon Collider Complex: • Proton Driver 2-16GeV; 1-4MW leading to 10 22 p /year • production target & Strong Field Capture • COOLING resultant m beam • m acceleration •Storage & collisions • Stopped m physics • physics From target, stored m • Higgs Factory mm= 40000 ee • Higher Energy Frontier R. Galea Ringberg Workshop 21-25 July, 2003 HIGH ENERGY MUON COLLIDER PARAMETERS Baseline parameters f or high energy muon colliders. From “Status of Muon Collider Research and Development and Future Plans,” Muon Collider Collaboration, C. M. Ankenbrandt et al., Phys. Rev. ST Accel. Beams 2, 081001 (1999). COM energy (TeV) p energy (GeV) p’s/bunch Bunches/fill Rep. rate (Hz) p pow er (MW) m/ bunch m power (MW) Wall power (MW) Collider circum. (m) Ave bending field (T) rms p/p (%) 6D (m)3 rms n ( mm mrad) * (cm) z (cm) r spot (mm) IP (mrad) Tune shif t nturn s (ef f ective) Luminosity (cm2 s1) R. Galea 0.4 16 2.5 1013 4 15 4 2 1012 4 120 1000 4.7 0.14 1.7 1010 50 2.6 2.6 2.6 1.0 0.044 700 1033 Ringberg Workshop 21-25 July, 2003 3.0 16 2.5 1013 4 15 4 2 1012 28 204 6000 5.2 0.16 1.7 1010 50 0.3 0.3 3.2 1.1 0.044 785 7 1034 ’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 ! R. Galea Ringberg Workshop 21-25 July, 2003 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. R. Galea Ringberg Workshop 21-25 July, 2003 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 R. Galea Ringberg Workshop 21-25 July, 2003 Cooling Ideas : Ionization Cooling RF m 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. R. Galea Ringberg Workshop 21-25 July, 2003 Longitudinal Cooling via Emittance Exchange Transform longitudinal phase space into transverse (know how to cool transverse) Wedge shaped absorber Bent solenoid produces dispersion R. Galea Ringberg Workshop 21-25 July, 2003 ‘Balbekov Ring’ There are significant developments in achieving 6D phase space via ionization cooling (R. Palmer, MUTAC03), but still far from 106 cooling factor. R. Galea Ringberg Workshop 21-25 July, 2003 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 R. Galea Ionization stops, muon too slow 1/2 from ionization Ringberg Workshop 21-25 July, 2003 Problems/comments: • • large dE/dx @ low kinetic energy low average density (gas) Apply E B to get below the dE/dx peak F q(E + v B) • • • dT rˆ dx m+ has the problem of Muonium formation (Mm) dominates over e-stripping in all gases except He m has the problem of Atomic capture 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 ) R. Galea Ringberg Workshop 21-25 July, 2003 Trajectories in detailed simulation Transverse motion Motion controlled by B field Lorentz angle drift, with nuclear scattering Fluctuations in energy results in emittance Final stages of muon trajectory in gas cell R. Galea Ringberg Workshop 21-25 July, 2003 Phase rotation sections Results of simulations to this point 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 with proton beam transverse to solenoids (capture low energy pion cloud). Not to scale !! R. Galea Ringberg Workshop 21-25 July, 2003 Yields & Emittance Results as of NUFACT02 Look at muons coming out of 11m cooling cell region after initial reacceleration. Yield: approx 0.002 m per 2GeV proton after cooling cell. Need to improve yield by factor 3 or more. Emittance: rms R. Galea 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 Ringberg Workshop 21-25 July, 2003 6D,N = 1.7 10-10 (m )3 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 R. Galea Look for a bunching in time Can we cool protons? Ringberg Workshop 21-25 July, 2003 4 MeV p R. Galea Ringberg Workshop 21-25 July, 2003 Accelerating grid Contains O(10-100nm) window Si detector To MCP R. Galea Proton beam Gas Ringbergcell Workshop 21-25 July, 2003 Vacuum chamber Assumed initial conditions •20nm C windows •700KeV protons •0.04atm He TOF=T0-(Tsi-TMCP) speed Kinetic energy 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 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) R. Galea Ringberg Workshop 21-25 July, 2003 Cool protons??? MC exp Flat constant Background 750ns # Events N i 58 82(55) i 5 45(49) i 55 194(77) i 42 124(77) i 300ns 400ns # Events N i 300ns 750ns # Events N i 200ns 400ns # Events N i 200ns Background exponential with m>0 R. Galea Ringberg Workshop 21-25 July, 2003 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. R. Galea Ringberg Workshop 21-25 July, 2003 Lab situated at MPI-WHI in Munich R. Galea Ringberg Workshop 21-25 July, 2003 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 • +… R. Galea Ringberg Workshop 21-25 July, 2003 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 m capture cross section m-+H Hm+ e+’s • muon initially captured in n=15 orbit, then cascades down to n=1. Transition n=2n=1 releases 2.2 KeV x-ray. Si drift detector Developed by MPI HLL R. Galea Ringberg Workshop 21-25 July, 2003 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. Kinetic Energy(KeV) Proton cooling test Time(ns) X(cm)