R&D towards a Multi-TeV Muon Collider

1. R&D towards a Multi-TeV Muon Collider Steve Geer • Introduction • Muon Collider Ingredients • Muon Collider / Neutrino Factory R&D • Muon Collider Specific R&D • Staging Possibilities • Summary

2. Steve Geer Fermilab April 23rd, 2007 page 2 Introduction • Muon Collider R&D has been conducted in the U.S. since 1997 by the Neutrino Factory & Muon Collider Collaboration. Note that Neutrino Factories & Muon Colliders require an intense cold muon beam, & much of the hardware development, and front-end design work, is common to both. • Since 1997 Fermilab has been one of 3 lead laboratories (with BNL & LBNL) overseeing the Neutrino Factory & Muon Collider R&D program, and has hosted the ionization cooling channel component development (MUCOOL). • The early U.S. MC/NF support peaked at ~8M$ / year, then fell to & remained at steady at ~3.6M$/year for several years. • The recent AARD sub-panel recommended increasing the MC/NF R&D support to ~8M$/yr.

3. Steve Geer Fermilab April 23rd, 2007 page 3 Motivation We want to make it possible for the HEP community to buildan affordable multi-TeV lepton collider. The Muon Collider concept is attractive because muons do not radiate as readily as electrons (mm / me ~ 207):  Circular (compact) multi-TeV Lepton Collider that would fit on an existing laboratory site  hope that Muon Colliders will be affordable. Very small beam energy spread enabling precise scans and width measurements  Muon Colliders may have a special role for precision measurements.  Present design work suggests that Muon Colliders with s=3-5 TeV and luminosities O(1034) cm-2 s-1 may one day be possible.

4. Steve Geer Fermilab April 23rd, 2007 page 4 The Challenge  To produce sufficient luminosity for an interesting physics program (L = 1034-1035 cm-2s-1 at s = 1-few TeV) will require very bright muon beams. This is challenging because: Muons produced as a tertiary beam that occupies a large longitudinal & transverse phase space. The beam must be cooled by a large factor: a longitudinal emittance reduction of about 14 & a transverse emittance reduction of about 400  6D reduction of ~14400400 = 2 106.  Muonsdecay (t0 = 2ms). Beam manipulation & acceleration must be rapid, and detector must be shielded.  If we can meet this challenge, along the way we will also have the technology for neutrino factories and for low energy muon experiments using up to ~1021 muons/year !

5. 2-4 MWProtonSource Hg-Jet Target Decay Channel Buncher Acceler- ation Helical Cooler RingCooler(s) BunchMerger Collider FinalCooler Pre Accel -erator Steve Geer Fermilab April 23rd, 2007 page 5 Muon Collider Ingredients • Proton Driver • primary beam on production target • Target, Capture, and Decay • create ; decay into  • Bunching & Phase Rotation • reduce E of bunch • Cooling • reduce 6D emittance • Acceleration • 130 MeV  up to 1.5 TeV • Storage Ring • store for ~1000 turs • One IP 3 TeV ~ 4 km

6. 1-4 MWProtonSource Hg-Jet Target n Decay Channel Buncher StorageRing Linear Cooler Pre Accel -erator 10-20GeV ~ 1 km 5-10 GeV Acceleration 1.5-5 GeV Steve Geer Fermilab April 23rd, 2007 page 6 Neutrino Factory Ingredients • Proton Driver • primary beam on production target • Target, Capture, and Decay • create ; decay into  • Bunching & Phase Rotation • reduce E of bunch • Cooling • reduce transverse emittance • Acceleration • 130 MeV  20 GeV • Storage Ring • store for 500 turns; long straight section

7. Steve Geer Fermilab April 23rd, 2007 page 7 Neutrino Factory vs Muon Collider Could be an 8 GeVH- linac delivering 2 MW … would need a rebunching ring to produce short (3ns)bunches. Neutrino Factories & Muon Colliders are linked by their common R&D and possible staging path.

8. Steve Geer Fermilab April 23rd, 2007 page 8 Target Design  Targetry design + R&D is common to Neutrino Factories & Muon Colliders  Targetry design developed in Neutrino Factory Studies 1 (in 2001) and 2 (in 2002): Target Station Schematic Target Station Design  Baseline design consists of a liquid Hg jet injected into a hybrid 20 T solenoid designed to operate with a 4 MW primary proton beam. Solid target options also being investigated.

9. In Europe (CERN/Grenoble) a Hg jet has been injected into a high-field solenoid at Grenoble. The field damps surface waves and improves the quality of the jet. 0 Tesla 13 Tesla t = 0 0.75 ms 2 ms 7 ms 18 ms In the US the NFMCC has studied the interaction of a 2.5 m/s mercury jet with a BNL proton beam, & measured the dispersal velocity & the time to reestablish the jet. Results are very encouraging. Steve Geer Fermilab April 23rd, 2007 page 9 Liquid Hg Jet R&D Next step is to test a 20 m/s Hg jet (required for NF/MC) within a 15 T solenoid exposed to an intense proton beam at CERN  MERIT Experiment. This will complete basic Hg-jet targetry R&D for Neutrino Factories & Muon Colliders

10. Steve Geer Fermilab April 23rd, 2007 page 10 MERIT Experiment Mercury circulation  Study interaction of a 1cm diam Hg-jet in a 15T solenoid with a proton beam (28TP@24GeV)  Magnet+Hg jet+optical system tested at MIT, now being installed at CERN.  Each beam pulse is a separate experiment … will take ~200 pulses.

11. RF RF Liq. H2 Liq. H2 Liq. H2 Cooling Channel Section Steve Geer Fermilab April 23rd, 2007 page 11 Ionization Cooling  Muons created within large phase-space volume. Beam cooling required before injecting into an accelerator.  Muons decay (tm = 2 ms)  Stochastic and electron cooling too slow. Need new cooling technique  ionization cooling.  Muons lose energy by dE/dx in material. Re-accelerate in the longitudinal direction  reduce transverse phase space (emittance). Coulomb scattering heats the beam  low Z absorber. Hydrogen is best.  Cooling channel designs continue toevolve, but typically consist of a multi-Tesla solenoid lattice to confine the muons, low-Z absorbers, and NCRF cavities.  A 50-100 m long channel like this is adequate for a NF (4D cooling). More technology needed for MC (6D Cooling)

12. Steve Geer Fermilab April 23rd, 2007 page 12 MUCOOL  The MUCOOL R&D program, hosted at FNAL, is to develop the components (RF and Absorbers) required for a muon ionization cooling channel To test MUCOOL components a new test area has been built (completed 2003)at end of FNAL 400 MeV Linac  RF power:201 MHz & 805 MHz  Liquid H2 absorber filling capability  5 T SC Solenoid with 30 cm bore (805 MHz Cavity fits inside) Will soon bring a proton beam to the area for low intensity, & eventually for high intensity beam (blast) tests of MUCOOL components

13. 201 MHz cavity 805 MHz pillbox cavity Steve Geer Fermilab April 23rd, 2007 page 13 MUCOOL rf R&D The 805-MHz and 201-MHz cavities installed at MTA, FNAL to study RF breakdown with external magnetic fields.

14. Steve Geer Fermilab April 23rd, 2007 page 14 MUCOOL Absorber R&D • Liquid H2 absorber, built at KEK, has been filled in the MTA. An improved version is now ready for testing • Thin windows that meet safety standards have been developed and tested (NIU and Univ. Mississippi) • LiH absorber R&D beginning KEK Absorber Thin Window Measurements LiH AbsorberDesign

15. Coupling Coils 1&2 Spectrometer solenoid 1 Matching coils 1&2 Matching coils 1&2 Spectrometer solenoid 2 Focus coils 1 Focus coils 2 Focus coils 3 m Beam PID TOF 0 Cherenkov TOF 1 RF cavities 1 RF cavities 2 Downstream TOF 2 particle ID: KL and SW Calorimeter VariableDiffuser Liquid Hydrogen absorbers 1,2,3 Incoming muon beam Trackers 1 & 2 measurement of emittance in and out Steve Geer Fermilab April 23rd, 2007 page 15 MICE Experiment 10% cooling of 200 MeV/c muons requires ~ 20 MV of RF

16. Steve Geer Fermilab April 23rd, 2007 page 16 MICE “Aspirational” Schedule

17. Steve Geer Fermilab April 23rd, 2007 page 17 ISS - IDS There has been a sequence of Neutrino Factory design studies:  Early Studies: US Feasibility Study 1 (sponsored by FNAL) Japanese NF Study CERN NF Study  Second Generation Studies US Feasibility Study 2 (sponsored by BNL: increased performance) US Feasibility Study 2a (APS neutrino study: reduced cost)  International Studies International Scoping Study (completed last year: prepare for IDS) International Design Study (Design Report by 2012)

18. Steve Geer Fermilab April 23rd, 2007 page 18 ISS Result  Now have an internationallyagreed upon baseline design  Similar to Study 2a design  Up to and including the cooling compatible with our present baseline Muon Collider design Store μ+ & μ- simultaneously • 1021 muon decays/yr • Eμ ~ 25 GeV

19. Steve Geer Fermilab April 23rd, 2007 page 19 Beyond a Neutrino Factory  We are on track for delivering a Neutrino Factory design report, based on tested technology, by ~2012  To go beyond this, and produce a Muon Collider design report willrequire the development of the concepts & technology for a much more ambitious cooling channel … and this is considered the greatest Muon Collider R&D challenge at present.  The next push on Muon Collider R&D is to try to meet this challenge: to arrive at a Muon Collider class cooling channel design based on tested technologies.

20. Steve Geer Fermilab April 23rd, 2007 page 20 Muon Collider Cooling Channel • Want to end up with 1 or 2 muon bunches / cycle to maximize luminosity. Old concept: make 1 bunch at the beginning & keep hold of it through the entire front-end requireslow frequency rf systems. We did not succeed in producing a practical, self-consistent cooling channel that reduced the emittance by the required factor of O(106). (Palmer et al)  In the last 2 years it has been realized that it is easier to start with many bunches, & combine them in the middle of the cooling scheme  first complete self-consistent MC cooling channel designs.

21. Steve Geer Fermilab April 23rd, 2007 page 21 New Ideas & a New Initiative •  The “baseline” MC cooling channel requires very high field HTS solenoids (50T ?), rf operating in high magnetic fields, and a so called “Guggenheim” (helical geometry) cooling channel. •  There are also new alternative ideas (many of which are coming fromMuons Inc) … that must be explored: rf cavities with high pressure gas, helical cooling magnets, reverse emittance exchange, parametric resonance cooling … • To explore/develope/prototype/test these cooling channel technologies, and guide the cooling cannel design towards an achievable and cost effective solution requires increased resources.  In July 2006 the Fermilab Director requested a Muon Collider Task Force be formed to develop the needed R&D plan and execute it as resources permit. An MCTF R&D proposal was given to the Director in October 2006:https://mctf.fnal.gov

22. Steve Geer Fermilab April 23rd, 2007 page 22 Muon Collider Task Force Muon ColliderAdvanced Accelerator R&D Proposal TASK FORCE35 members MUONS INC. 5 collaborators BNL 6 collaborators LBNL 4 collaborators ANL 1 collaborator JLAB 5 collaborators

23. Steve Geer Fermilab April 23rd, 2007 page 23 Proposed MCTF Activities – 1 • Collider Design and Simulations to establish the muon cooling requirements. We will take a fresh look at the overall Muon Collider scheme. In addition to establishing the ionization cooling requirements, we will also identify the remaining muon source and collider design and performance issues. • Component Development: We will develop and bench test the components needed for the 6D cooling channel. • Beam Tests and Experiments: We will perform beam tests of the components. For that we will build a proton beam line for high-intensity tests of LiH absorbers and pressurized RF cavities. Later, we will design and build a muon production, collection and transport system. 250-300 MeV/c muons will be used in the 6D ionization cooling demonstration experiment.

24. Steve Geer Fermilab April 23rd, 2007 page 24 MCTF Scope • Current FY07 guidance: 750k$ total (p-line and MTA exp) • FY08 guidance: 2.2M$ M&S + 3.9M$ SWF

25. Steve Geer Fermilab April 23rd, 2007 page 25 Proposed MCTF Activities - 2 Cooling &MC Design Experimental R&D Magnet R&D MC Design: -Optics collider -Beam-beam in Coll -Final mcool/Li?/res? -Main mcool/inj/extr -Injection/rad Coll -Racetrack -20GeV beam mnpl -source/transport MTA studies: -build MTA p-line -beam dump -MTA infrastructure -200/800 cavity test -absorber LH,He/LiH HCC: -design -prototype/testing -fabrication/test HTS Solenoid: -material research -insert design -insert fabricat/test -solenoid design -prototype/test 6D Cooling Expt: -design work -m-product’n/capture -m-transport/match -m-diagnostics -HCC cryo/PSs/QPS -beam dump/radiation -windows -absorber system Cooling Design: -realistic modeling -simul 6DHCC exper -radiation/diagn/RF -inj/extr/transport -error sensitivity 12T Dipole: -specs -design -prototype/test

26. Steve Geer Fermilab April 23rd, 2007 page 26 Staging There are several possibilities offering a flexible path to a multi-TeVmuon collider:  Low energy muon program Might begin with a muon to electron conversion experiment using the existing proton complex  HINS (8 GeV proton driver, 2MW ) Upgraded low energy muon experiment (s) Other experiments (kaons, neutrons … )  Neutrino Factory Add phase rotation, cooling and low energy acceleration system  Higgs Factory Add Muon Collider cooling channel and more acceleration  Multi-TeV Muon Collider More acceleration, possibly modifed cooling channel

27. Steve Geer Fermilab April 23rd, 2007 page 27 Summary In our present baseline designs, the output from a Neutrino Factory cooling channel is the input to a Muon Collider cooling channel. Neutrino Factory R&D has been successfully globalized (MERIT,MICE, ISS-IDS) In the next few years (by ~2010-2012) the basic Neutrino Factory R&D should be completed, but we need a lot more technology for a Muon Collider. The main Muon Collider challenge at this stage of the R&D is to develop a Muon Collider class cooling channel design based on tested technologies. In July 2006 Pier charged the Muon Collider Task Force to create an R&D plan and execute it, as resources permit. The scope of the plan is ~5M$/year.

28. Steve Geer 8th ICFA Seminar on Future Perspectives in HEP. Sept 28 - October 1, 2005 Daegu, Korea 28 Muon Collider Parameter Table C. Ankenbrandt et al., PRST-AB 2, 081001 (1999)