1. MCTF Steve Geer SLAC/LBNL November, 2009 1 Muon Colliders  

2. MCTF Physics Landscape Steve Geer SLAC/LBNL November, 2009 2

3. MCTF Decision Tree Steve Geer SLAC/LBNL November, 2009 3 Pierre Oddone 0.5 TeV e + e - 3 TeV e + e - 3-4 TeV  +  -

4. MCTF Muon Collider Motivation  If we can build a multi-TeV muon collider it’s an attractive option because muons don’t radiate as readily as electrons (m  / m e ~ 207): - COMPACT Fits on laboratory site - MULTI-PASS ACCELERATION Cost Effective (e.g. 10 passes → factor 10 less linac) - MULTIPASS COLLISIONS IN A RING (~1000 turns) Relaxed emittance requirements & hence tolerances - NARROW ENERGY SPREAD Precision scans - TWO DETECTORS (2 IPs)  -  T bunch ~ 10  s … (e.g. 4 TeV collider) Lots of time for readout Backgrounds don’t pile up - (m  /m e ) 2 = ~40000 Enhanced s-channel rates for Higgs-like particles Steve Geer SLAC/LBNL November, 2009 4 COST PHYSICS

5. MCTF Muon Colliders are Compact Steve Geer SLAC/LBNL November, 2009 5 4 TeV 0.5 TeV 3 TeV

6. MCTF Narrow Energy Spread Beamstrahlung in any e+e- collider  E/E   2 Steve Geer SLAC/LBNL November, 2009 6 Shiltsev

7. MCTF Challenges ● Muons are born within a large phase space (  →  ) - To obtain luminosities O(10 34 ) cm -2 s -1, need to reduce initial phase space by O(10 6 ) ● Muons Decay (  0 = 2  s) - Everything must be done fast → need ionization cooling - Must deal with decay electrons - Above ~3 TeV, must be careful about decay neutrinos ! Steve Geer SLAC/LBNL November, 2009 7

8. MCTF Muon Collider Schematic Steve Geer SLAC/LBNL November, 2009 8 Proton source: Upgraded PROJECT X (4 MW, 2±1 ns long bunches) 10 21 muons per year that fit within the acceptance of an accelerator √s = 3 TeV Circumference = 4.5km L = 3×10 34 cm -2 s -1  /bunch = 2x10 12  (p)/p = 0.1%  * = 5mm Rep Rate = 12Hz

9. MCTF Target Facility Design Steve Geer SLAC/LBNL November, 2009 9 A 4MW target station design study was part of “Neutrino Factory Study 1” in 2000  ORNL/TM2001/124 Facility studied was 49m long = target hall & decay channel, shielding, solenoids, remote handling & target systems. Target: liquid Hg jet inside 20T solenoid, identified as one of the main Neutrino Factory challenges requiring proof-of-principle demonstration. Beam dump = liquid Hg pool. Some design studies started. 4MW Target Station Design V. Graves, ORNL T. Davonne, RAL Proton Hg Beam Dump

10. MCTF MERcury Intense Target Experiment (MERIT) Steve Geer SLAC/LBNL November, 2009 10 Proof-of-principle demonstration of a liquid Hg jet target in high-field solenoid ran at CERN PS in Fall 2007. Successfully demonstrated a 20m/s liquid Hg jet injected into a 15T solenoid, & hit with a suitably intense beam (115 KJ / pulse !). Results suggest this technology OK for beam powers up to 8MW with rep. rate of 70Hz ! Hg jet in a 15T solenoid Measured disruption length = 28 cm 1 cm

11. MCTF Front-End Specifications Steve Geer SLAC/LBNL November, 2009 11 ParameterDriftBuncherRotatorCooler Length (m)56.431.53675 Focusing (T)2222.5 (ASOL) RF f (MHz)360  240240  202201.25 RF G (MV/m)0  151516 Total RF (V)126360800 ± → ± →   /p within reference acceptance = 0.085 at end of cooler →  1.5 10 21 μ/year

12. MCTF Front-End Simulation Results Steve Geer SLAC/LBNL November, 2009 12 Neuffer

13. MCTF Ionization Cooling Steve Geer SLAC/LBNL November, 2009 13  Must cool fast (before muons decay)  Muons lose energy by in material (dE/dx). Re-accelerate in longitudinal direction  reduce transverse phase space (emittance). Coulomb scattering heats beam  low Z absorber. Hydrogen is best, but LiH also OK for the early part of the cooling channel. CoolingHeating

14. MCTF MuCool Steve Geer SLAC/LBNL November, 2009 14  Developing & bench testing cooling channel components  MuCool Test Area at end of FNAL linac is a unique facility: -Liquid H2 handling -RF power at 805 MHz -RF power at 201 MHz -5T solenoid (805 MHz fits in bore) -Beam from linac (soon) Liq. H2 absorber MTA 42cm  Be RF window New beamline

15. MCTF RF in Magnetic Field: 805 MHz Results Steve Geer SLAC/LBNL November, 2009 15 Peak Magnetic Field in T at the Window >2X Reduction @ required field  Data reproducible & seem to follow universal curve.  Possible solutions: - special surfaces (e.g. beryllium) -Surface treatment (e.g. ALD) - Magnetic insulation  Effect is not seen in cavities filled with high pressure hydrogen gas (Johnson & Derbenev) – possible solution (but needs to be tested in a beam – coming soon)  When vac. copper cavities operate in multi Tesla co-axial mag. field, the maximum operating gradient is reduced.

16. MCTF MICE Steve Geer SLAC/LBNL November, 2009 16  Ionization Cooling Instrumentation GOALS: Build a section of cooling channel capable of giving the desired performance for a Neutrino Factory & test in a muon beam. Measure performance in various modes of operation.  Multi-stage expt.  First stage being installed at purpose-built muon beam at RAL (first beam to hall March 2008).  10% cooling measured to ±1%. Anticipate completed ~2011/12  Beam Line Complete  First Beam 3/08  Running now  PID Installed  CKOV  TOF  EM Cal  First Spectrometer  Spring 2010 Spectrometer Solenoid being assembled

17. MCTF 6D Cooling Steve Geer SLAC/LBNL November, 2009 17  MC designs require the muon beam to be cooled by ~ O (10 6 ) in 6D  Ionization cooling reduces transverse (4D) phase space.  To also cool longitudinal phase space (6D) must mix degrees of freedom as the cooling proceeds  This can be accomplished with solenoid coils arranged in a helix, or with solenoid coils tilted. Palmer Alexhin & Fernow

18. MCTF 6D Cooling Channel Scheme Steve Geer SLAC/LBNL November, 2009 18 Palmer

19. MCTF 6D Cooling Channel Development Steve Geer SLAC/LBNL November, 2009 19 Detailed Simulations for candidate 6D cooling schemes Magnet develop- ment for 6D cooling channels HCC magnet 4 coil test REQUIRES BEYOND STATE OF ART TECHNOLOGY → Ongoing R&D FOFO Snake - Alexhin Helical Cooling Channel- Muons Inc.

20. MCTF Final Cooling Steve Geer SLAC/LBNL November, 2009 20  When the emittance is very small, to continue cooling we need very high field solenoids (to continue winning against scattering)  For fields up to ~50T, the final luminosity is ~ prop-ortional to the solenoid field at the end of the channel.  For higher fields we no longer expect to continue to win (limited by beam- beam tune shift).

21. MCTF The Promise of HTS Steve Geer SLAC/LBNL November, 2009 21

22. MCTF HTS Solenoid R&D Steve Geer SLAC/LBNL November, 2009 22 NHMFL test coil LBL Test Coil FNAL test cable. Test degradation of J c in the cabling process

23. MCTF Acceleration Steve Geer SLAC/LBNL November, 2009 23 0.1 1 2 5 10 20 50 AVERAGE GRADIENT (MV/m) MUON SURVIVAL FRACTION Bogacz 0.2 0.4 0.6 0.8 1.0 Accelerating muons from 3 GeV to 2 TeV Example: TESLA cavities: Real estate gradient ~31 MV/m → 97% survival ● Early Acceleration (to 25 GeV ?) could be the same as NF. Needs study. ● Main Acceleration – Attractive Candidates - RLAs (extension of NF accel. scheme ?) - Rapid cycling synchrotron – needs magnet R&D - Fast ramping RLA ● Options need study → particle tracking, collective effects, cavity loading,...

24. MCTF Collider Ring Muons circulate for ~1000 turns in the ring Need high field dipoles operating in decay back- grounds → R&D First lattice designs exist  New ideas → conceptual designs for various options  Comparison of different schemes, choice of the baseline  Detailed lattice design with tuning and correction “knobs”  Dynamic aperture studies with magnet nonlinearities, misalignments and their correction  Transient beam-beam effect compensation  Coherent instabilities analysis WE ARE HERE DESIGN PROCESS Steve Geer SLAC/LBNL November, 2009 24

25. MCTF Neutrino Radiation Steve Geer SLAC/LBNL November, 2009 25  With L ~ E 2 →  OK at √s = 1 TeV  OK at √s = 3 TeV if D = 200m  Above 3 TeV need to pay attention (wobble beam, lower  *, higher B ring, … )

26. MCTF Background from Muon Decay Steve Geer SLAC/LBNL November, 2009 26 As the decay electrons respond to the fields of the final focus system they lose 20% of their energy by radiating on average 500 synchrotron photons with a mean energy of ~500 MeV … & are then swept out of the beampipe.  2 x 10 12 muons/bunch  2 x 10 5 decays/m  Electron decay angles O(10)  rad  Mean electron energy = 700 GeV Mean energy = 700 GeV 2  2 TeV Collider Electron Energy (GeV) 0 500 1000 1500 2000 Number of Decays  - → e - e 

27. MCTF Detector Backgrounds Steve Geer SLAC/LBNL November, 2009 27  Muon Collider detector backgrounds were studied actively ~10 years ago (1996-1997). The most detailed work was done for a 2  2 TeV Collider →  s=4 TeV.  Since muons decay (  2TeV =42ms), there is a large background from the decay electrons which must be shielded.  The electron decay angles are O(10) microradians – they typically stay inside the beampipe for about 6m. Hence decay electrons born within a few meters of the IP are benign.  Shielding strategy: sweep the electrons born further than ~6m from the IP into ~6m of shielding.

28. MCTF Background Simulations Steve Geer SLAC/LBNL November, 2009 28 Shielding design group & final focus design group worked closely together & iterated Used two simulation codes (MARS & GEANT), which gave consistent results Shielding design & simulation work done by two experts (Mokhov & Stumer) in great detail, & involved several person-years of effort.

29. MCTF Final Focus Setup Steve Geer SLAC/LBNL November, 2009 29  Fate of electrons born in the 130m long straight section: 62% interact upstream of shielding, 30% interact in early part of shielding, 2% interact in last part, 10% pass through IP without interacting.

30. MCTF IP Region Steve Geer SLAC/LBNL November, 2009 30

31. MCTF More Shielding Details Steve Geer SLAC/LBNL November, 2009 31 r=4cm Z=4m Designed so that, viewed from the IP, the inner shielding surfaces are not directly visible.

32. MCTF 4 TeV Collider Backgrounds Steve Geer SLAC/LBNL November, 2009 32 Background calculations & shielding optimization was performed using (independently) MARS & GEANT codes … the two calculations were in broad agreement with each other (although the designs were different in detail). Results from Summer 1996 GEANT MARS I. Stumer N. Mokhov

33. MCTF 4 TeV Collider Backgrounds Steve Geer SLAC/LBNL November, 2009 33 r (cm)  np  e  527001200.050.92.31.7 107501100.200.40.7 153501000.130.4 202101000.130.30.1 50701200.080.050.02 10031500.040.0030.008 calo0.003 muon 0.0003 GEANT (I. Stumer) Results from LBL Workshop, Spring 1997 Particles/cm 2 from one bunch with 2  10 12 muons (2 TeV)

34. MCTF Occupancies in 300x300  m 2 Pixels Steve Geer SLAC/LBNL November, 2009 34 TOTALCHARGED

35. MCTF Vertex Detector Hit Density Steve Geer SLAC/LBNL November, 2009 35  Consider a layer of Silicon at a radius of 10 cm: GEANT Results (I. Stumer) for radial particle fuxes per crossing: 750 photons/cm 2  2.3 hits/cm 2 110 neutrons/cm 2  0.1 hits/cm 2 1.3 charged tracks/cm 2  1.3 hits/cm 2 TOTAL 3.7 hits/cm 2  0.4% occupancy in 300x300  m 2 pixels  MARS predictions for radiation dose at 10 cm for a 2x2 TeV Collider comparable to at LHC with L=10 34 cm -2 s -1  At 5cm radius: 13.2 hits/cm 2  1.3% occupancy  For comparison with CLIC (later) … at r = 3cm hit density about ×2 higher than at 5cm → ~20 hits/cm 2 → 0.2 hits/mm 2

36. MCTF Pixel Micro-Telescope Idea Steve Geer SLAC/LBNL November, 2009 36 S. Geer, J. Chapman: FERMILAB-Conf-96-375 Photon & neutron fluxes in inner tracker large but mean energies O(MeV) & radial fluxes ~ longitudinal fluxes (  isotropic) Clock 2 layers out at variable clock speed (to maintain pointing) & take coincidence. Blind to soft photon hits & tracks that don’t come from IP

37. MCTF Pixel Micro-Telescope Simulation - 1 Steve Geer SLAC/LBNL November, 2009 37

38. MCTF Pixel Micro-Telescope Simulation - 2 Steve Geer SLAC/LBNL November, 2009 38

39. MCTF TPC Steve Geer SLAC/LBNL November, 2009 39  Exploit 10  s between crossings  Large neutron flux – gas must not contain hydrogen: 90% Ne + 10% CF 4  V drift = 9.4 cm/  s with E = 1500 V/cm. Ion buildup   E/E = 0.7%  Cut on pulse height removes photon & neutron induced recoils V. Tchernatine

40. MCTF Calorimeter Backgrounds Steve Geer SLAC/LBNL November, 2009 40 Electromagnetic: Consider calorimeter at r=120 cm, 25 r.l. deep, 4m long, 2  2 cm 2 cells:  GEANT  400 photons/crossing with ~1 MeV  ~400 MeV   E ~  (2 ) = 30 MeV  For a shower occupying 4 towers: = 1.6 GeV and  E = 60 MeV Hadronic: Consider calorimeter at r=150 cm, 2.5m deep (~10 ), covering 30-150 degrees, 5  5 cm 2 cells:  ~ 400 MeV   E ~  (2 ) = O(100 MeV) These estimates were made summer 1996, before further improvements to final focus + shielding reduced backgrounds by an order of magnitude … so guess background fluctuations reduced by  3 compared with above.

41. MCTF Bethe-Heitler Muons (  Z  Z  +  - ) Special concern: hard interactions (catastrophic brem.) of energetic muons travelling ~parallel to the beam, produced by BH pair production. Believe that this back- ground can be mitigated using arrival-times, pushing calorimeter to larger radius, & spike removal by pattern recognition … but this needs to be simulated Steve Geer SLAC/LBNL November, 2009 41

42. MCTF Comparison with CLIC Steve Geer SLAC/LBNL November, 2009 42 We are not yet in a position to make an apples-to-apples comparison with CLIC, but ….. hits/mm 2 /bunch train 30mm  O(1) hit/mm 2 /bunch train  FROM CLIC Machine- Detector interface studies: CLIC NOT AN APPLES-to- APPLES COMPARISON … BUT … Background hit densities appear to be similar to MC … so there may be many detector design issues in common between the 2 machines Note: CLIC shielding cone = 7 o c.f. 20 o for MC (but we hope to improve on this)

43. MCTF MC R&D – The Next Step In the last few years MC-specific R&D has been pursued in the U.S. by Neutrino Factory & Muon Collider Collaboration (NFMCC) & Muon Collider Task Force (MCTF) Last December the NFMCC+MCTF community submitted to DOE a proposal for the next 5 years of R&D, requesting a greatly enhanced activity, aimed at proving MC feasibility on a timescale relevant for future decisions about multi-TeV lepton colliders. Steve Geer SLAC/LBNL November, 2009 43

44. MCTF NFMCC/MCTF Joint 5-Year Plan ● Deliverables in ~5 years: -Muon Collider Design Feasibility Report - Hardware R&D results → technology choice - Cost estimate - Also contributions to the IDS-NF RDR ● Will address key R&D issues, including - Maximum RF gradients in magnetic field - Magnet designs for cooling, acceltn, collider - 6D cooling section prototype & bench test - Full start-to-end simulations based on technologies in hand, or achievable with a specified R&D program ● Funding increase needed to ~20M$/yr (about 3x present level); total cost 90M$ Steve Geer SLAC/LBNL November, 2009 44

45. MCTF R&D – Ongoing NFMCC/MCTF HISTORY & FUTURE PROPOSAL Steve Geer SLAC/LBNL November, 2009 45

46. MCTF Anticipated Progress Key component models NOW 5 YEARS Steve Geer SLAC/LBNL November, 2009 46

47. MCTF Aspirational Bigger Picture Steve Geer SLAC/LBNL November, 2009 47

48. MCTF Muon Collider R&D: A National Program Steve Geer SLAC/LBNL November, 2009 48

49. MCTF Final Remarks Steady progress on the Front-End develop- ment for Muon Colliders - Cooling channel design concepts - NF R&D (IDS-NF, MERIT, MICE, … ) The time has come to ramp up the Muon Collider specific R&D → a National Program There are many challenges to be overcome - RF in magnetic fields & 6D Cooling Channel - Cost effective acceleration scheme - Collider Ring - Detector/Backgrounds optimization The incentive to meet these challenges is great → “5 Year Plan” → Design Feasibility Study Steve Geer SLAC/LBNL November, 2009 49

50. MCTF   3 4 4 GeV NF 25 GeV NF Illustrative Staging Scenario 4MW multi-GeV Proton Source Accumulation & Rebunching Steve Geer CERN Neutrino Workshop October 1-3, 2009 50

51. MCTF Muon Collider Parameters Steve Geer SLAC/LBNL November, 2009 51