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Prospects for an Energy-Frontier Muon Collider

Prospects for an Energy-Frontier Muon Collider. Tom Roberts Muons, Inc. Illinois Institute of Technology. Outline. Background Why muons? The major challenges Surmounting the challenges Recent innovations that have improved the prospects for success

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Prospects for an Energy-Frontier Muon Collider

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  1. Prospects for an Energy-Frontier Muon Collider Tom Roberts Muons, Inc. Illinois Institute of Technology Prospects for a Muon Collider

  2. Outline • Background • Why muons? • The major challenges • Surmounting the challenges • Recent innovations that have improved the prospects for success • Viewgraph-level design of a Muon Collider • Current R&D Efforts • Summary Prospects for a Muon Collider

  3. Background Reminders Historically, every significant increase in energyhas taught us something completely new. Every new type of particle beam has alsotaught us something completely new. The LHC is turning on later this year, so the “energy frontier” is above 14 TeV for protons,or above ~1.5 TeV for leptons. Prospects for a Muon Collider

  4. The Livingston Plot X 5 TeV MC Constituent Center-of-Mass Energy X ILC 2025 Panofsky and Breidenbach, Rev. Mod. Phys. 71, s121-s132 (1999) Prospects for a Muon Collider

  5. Why Muons? • Electrons have problems at the energy frontier • At the TeV scale, radiative processes limit both energy and luminosity for electrons • Synchrotron radiation losses  linear, large, and very expensive • Beamstrahlung ~ E2, approaches the beam energy in one crossinglow luminosity at peak energy, huge beam energy spread • Remember those beautiful, narrow peaks for the J/Ψ? They won’t happen again because: • The beam energy spread is very large • Resonances above 2MW will have large weak-decay widths • Protons have problems at the energy frontier • Without some tremendous breakthrough in high-field magnets, the machine must be truly enormous (expensive) • As composite particles, beam energy must be considerably higher than for leptons Prospects for a Muon Collider

  6. Muons • Clearly a whole new window into electroweak processes • A path to the energy frontier • Radiative processes are far from limiting (as for electrons) • Circular machine is possible, as are recirculating linacs • Lepton, so beam energy and machine size are significantly lower than for protons • For S-channel Higgs production, cross-section~ m2 – 40,000 times larger than for e+e-. Prospects for a Muon Collider

  7. Muons A 5 TeV muon collider could fit on the existingFermilab site. [Ankenbrandt et al., PRST-AB 2, 081001 (1999)] Prospects for a Muon Collider

  8. The Major Challenges • Muons decay in 2.2 microseconds • Muons are created with a very large emittance, too large for conventional accelerators, too large to give reasonable luminosity • Muon production from 8-40 GeV protons scales roughly as proton beam power, independent of energy • A 1 to 4 Megawatt proton beam is required • The production target is also a challenge • Muons decay into an electron plus neutrinos • Electron backgrounds in detector • Neutrino radiation problem (!) Prospects for a Muon Collider

  9. Reducing the Phase Space – “Cooling” • Loosely: the muons produced occupy the size of a beach ball (60 cm), the ILC accelerating cavities can accept a BB (4 mm) • take advantage of ILC R&D and optimization. • overall reduction in phase space ~106. • Luminosity ~ N2·ε┴-2 so lower transverse emittance permits a reduction in N (which reduces other problems). • Must select a process that avoids Liouville’s theorem. • Must select a method consistent with the muon lifetime (2.2 μsec). • Desirable to select a method consistent with the peak momentum of the produced muons (~300 MeV/c). Prospects for a Muon Collider

  10. Muon Ionization Cooling p┴ reduced, p|| unchanged Absorber dp/dz || -p RF Cavity dp/dz || +z • Alternate absorbers and RF cavities • RF cavities restore the energy lost in the absorbers • A factor of 1/e reduction in transverse phase space occurs when the total energy lost in absorbers equals the beam energy (both planes) • Optimal energy corresponds to a momentum of 100-250 MeV/c • Works only for muons (electrons shower, hadrons interact) • Transverse cooling only (small longitudinal heating due to straggling) (Skrinsky & Parkhomchuk, 1981) Prospects for a Muon Collider

  11. Muon Ionization Cooling • Want: • Lower β┴ (stronger focusing at the absorber) • Minimize multiple scattering • Maximize energy loss Transverse Emittance change per unit length in the absorber: Heating term (multiple scattering) Cooling term (energy loss) Lattice design Absorber Material Here is the normalized emittance, Eµis themuon energy, dEµ/ds and X0 are the energy loss and radiation length of the absorber material, is the transverse beta-function of the magnetic channel, and  is the particle velocity. Prospects for a Muon Collider

  12. Absorber Materials Fcool ~ (Energy Loss) / (Multiple Scattering) Prospects for a Muon Collider

  13. Emittance Exchange Ionization cooling is only transverse. To get longitudinal cooling,use emittance exchange. Prospects for a Muon Collider

  14. Innovation: Helical Cooling Channel These coils just surround the beam region. All coils are normal to the Z axis; their centers are offset in X and Y to form the helix. The helical solenoid is filled with a continuous absorber, and perhaps with RF cavities. Beam Follows Helix • Cools in all 6 dimensions – higher-energy particles have longer path length in the absorber • A remarkable thing occurs: for specific values of the geometry, the solenoid, helical dipole, and helical quadrupole fields are all correct. • With absorber and RF, parameters remain constant; with absorber only, parameters decrease with momentum. • Acceptance is quite large compared to most accelerator structures. Prospects for a Muon Collider

  15. Four sequential HCCs with decreasing diameter and period, increasing field (8 T max) Emittance reduction is 50,000 over 160 m(~15% decay) In the analogy of starting with a beach ball and needing a BB, this is a small marble (~1 cm dia.) HCC Simulation Prospects for a Muon Collider

  16. Related Innovation: Guggenheim Cooling Channel • Helix with radius >> period • Also capable of emittance exchange • More like a ring cooler that has been “stretched” vertically Figure is mine; concept is Palmer et al, BNL Prospects for a Muon Collider

  17. Electrode breakdown region Paschen region Innovation: High Pressure Gas RF Cavities • High-pressure hydrogen reduces breakdown via the Paschen effect • No decrease in maximum gradient with magnetic field • Need beam tests to show HPRF actually works for this application. 805MHz Prospects for a Muon Collider

  18. Innovation: High Pressure Gas RF Cavities • Copper plated, stainless-steel, 805 MHz test cell • H2 gas to 1600 psi and 77 K • Paschen curve verified (at Fermilab’s Lab G and MuCool Test Area) • Maximum gradient limited by breakdown of metal • Fast conditioning seen • Unlike vacuum cavities, there’s no measurable limitation for magnetic field! Prospects for a Muon Collider

  19. Understanding RF Breakdown Scanning electron microscope images; Be (top) and Mo (bottom). Prospects for a Muon Collider

  20. x Innovation: Parametric Resonance Ionization Cooling Clever method to greatly reduce  without increased magnetic fields. Excite ½ integer parametric resonance (in Linac or ring) • Like vertical rigid pendulum or ½-integer extraction • Elliptical phase space motion becomes hyperbolic • Use xx’=const to reduce x, increase x’ • Use IC to reduce x’ Detuning issues are being addressed (chromatic and spherical aberrations, space-charge tune spread). Simulations are underway. Smaller beams from 6D HCC cooling are essential for this to work! X’ X’ X X Prospects for a Muon Collider

  21. IncidentMuon Beam Wedge Abs Evacuated Dipole Innovation: Reverse Emittance Exchange • p(cooling)~200MeV/c, p(colliding)~2.5 TeV/c  room in Δp/p space • After cooling and acceleration, the beam has much smaller longitudinal emittance than necessary. • Reduce transverse emittance to increase luminosity, trading it for increased longitudinal emittance (limited by accelerator acceptance and interaction point *). Prospects for a Muon Collider

  22. p Drift RF t Cooled at 100 MeV/c RF at 20 GeV Coalesced in 20 GeV ring 1.3 GHz Bunch Coalescing at 20 GeV Innovation: Bunch Coalescing • Start with ~100 MeV/c cooled bunch train. • Accelerate to ~20 GeV/c with high-frequency RF. • Apply low-frequency RF to rotate the bunches longitudinally. • Permit them to drift together in time. • Avoids space charge problems at low energy. Prospects for a Muon Collider

  23. Possible 8 GeV Project X Linac ~ 700m Active Length Bunching Ring Target and Muon Cooling Channel Recirculating Linac for Neutrino Factory Innovation: Dual-Use Linac • Fermilab is considering “Project X”, a high-intensity 8 GeV superconducting linac • Use it also to accelerate muons (after cooling) NeutrinoFactoryaimed atSoudan, MN Prospects for a Muon Collider

  24. Innovation: Pulsed Recirculating Linac • Accelerating from 20 GeV to 2,500 GeV requires a lot of RF! • Muon decay dictates high ratio of RF/length. • A “dogbone” recirculating linac is a reasonable trade-off between cost, size, and muon decay. • By pulsing the quadrupoles of the linac, more passes can be made without losing transverse focusing. • This linac is several km long, so pulsing is feasible. • With careful design this can handle both μ+ and μ­ (time offset in RF cavities, FODO vs DOFO lattice, travel opposite directions in arcs). Injection Extraction Linac Prospects for a Muon Collider

  25. Innovation: High-Field HTS Superconducting Magnets • The high-temperature superconductors have a remarkable property: at low temperature (2-4 K) they sustain a high current density at large magnetic fields. • Measured up to ~40 T, expected to hold to even higher fields. • It is likely that solenoids in the range of 30 T to 50 T can be constructed. • Higher field  lower , so lower emittance can be achieved via ionization cooling. • These materials are a challenge to work with… Prospects for a Muon Collider

  26. Many New Arrows in the Quiver • New Ionization Cooling Techniques • Helical Cooling Channel • Momentum-dependent Helical Cooling Channel • Guggenheim cooling channel • Ionization cooling using a parametric resonance • Methods to manipulate phase space partitions • Reverse emittance exchange using absorbers • Bunch coalescing (neutrino factory and muon collider share injector) • Technology for better cooling • Pressurized RF cavities • High Temperature Superconductor for up to 50 T magnets • Acceleration Techniques • Dual-use Linac • Pulsed Recirculating Linac Prospects for a Muon Collider

  27. Conceptual Block Diagram of a Muon Collider Proton Driver(8-40 GeV) ProductionTarget Pion Capture, Decay Channel,Phase Rotation, and Pre-Cooling Muon Ionization Cooling Acceleration(0.2 to 20 GeV) Reverse EmittanceExchange Bunch Coalescing Acceleration (20 to 2,500 GeV) Storage Ring andInteraction Regions Experiments Must of course deal with both μ+ and μ-. Prospects for a Muon Collider

  28. Fernow-Neuffer Plot Start Cooling: After Capture, Decay, Phase Rotation, Pre-Cooling End Cooling:Start Acceleration to2.5 TeV HCC 400 MHz REMEX &Coalescing HCC 800 MHz PIC HCC 1600 MHz AccelerationTo 20 GeV Prospects for a Muon Collider

  29. Viewgraph-level Design 2.5 + 2.5 TeV muon storage ring with two IRs 1 km radius (= Fermilab Main Ring,but it’s not deep enough) L ~ 1035 cm-2 s-1 μ+ 2.5 km ILC-like linacs 10 recirculating arcs In one tunnel μ– Final cooling, preacceleration Helical cooling channel Target, pion capture, Phase rotation Proton driver Prospects for a Muon Collider

  30. Related Facility: Neutrino Factory • Muons in a storage ring with a long straight section aimed at the far neutrino detector • Concept is more fleshed out that a muon collider • Cheaper, of striking current interest, perhaps more feasible • Thousands of times more neutrino intensity than alternatives • Higher energy neutrinos, with narrower energy spectrum • Essentially perfect purity (no π decays) – great for wrong-sign appearance measurements of oscillation • Near detector looks a lot like old fixed-target hadron experiments: • 30 cm liquid hydrogen target • Event rate ~ 1-100 Hz • Must be careful about material (spontaneous muons!) Prospects for a Muon Collider

  31. Neutrino Factory Prospects for a Muon Collider

  32. Current R&D Efforts • Six different (but greatly overlapping) collaborations, more than 200 physicists: • Neutrino Factory and Muon Collider Collab. • Umbrella U.S. collaboration • MERIT Collab. • Mercury jet target in 15 Tesla solenoid • 24 GeV protons at CERN • Analyzing data • MuCool Collab. • Engineering studies for individual components • ~4 years of studies so far, at Fermilab • Test beam (400 MeV H-) ~ SUMMER • MICE Collab. • Single-particle demonstration of emittance reduction • First muon Beam (140-300 MeV/c μ) “Real Soon Now” • MANX Collab. • Just forming • Fermilab’s Muon Collider task Force • Plus other Neutrino Factory organizations Prospects for a Muon Collider

  33. Solenoid Jet Chamber Syringe Pump Secondary Containment Proton Beam 1 2 3 4 Merit – Target Test • High-power target test using a mercury jet in a 15 T solenoid, at CERN • Data taking completed last fall, data analysis in progress • Preliminary conclusion: concept validated up to 4 MW at 50 Hz Prospects for a Muon Collider

  34. MuCool Tests in progress at Fermilab MuCool Test Area (MTA) near Linac, with full-scale (201 MHz) and 1/4-scale (805 MHz) closed-cell (pillbox) cavities with novel Be windows for higher on-axis field Prospects for a Muon Collider

  35. MICE(~10% 4d Cooling in 5.5 m) • Installation in ISIS R5.2 is progressing • Beamline commissioning “Real soon now” (2-3 weeks) • A month or two until beamline is complete • Summer or fall until trackers are complete Prospects for a Muon Collider

  36. The MANX Experiment(~500% 6d Cooling in 4 m) • Purpose is to demonstrate the Helical Cooling Channel. • Could well become a “Phase III” of MICE (total is 2.5 m longer than MICE Stage VI – fits in hall). Prospects for a Muon Collider

  37. Summary • A number of clever innovations have made a Muon Collider much more feasible than previously thought. • To make it possible to actually construct such a new facility, an ongoing program of research and development is essential. • We are hosting a Low Emittance Muon Collider Workshop, at Fermilab in April. • There is lots to do – come join us! http://www.muonsinc.com Prospects for a Muon Collider

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