R&D towards a Multi-TeV Muon Collider Steve Geer 1.Introduction 2.Muon Collider Ingredients 3.Muon Collider / Neutrino Factory R&D 4.Muon Collider Specific R&D 5.Staging Possibilities 6.Summary

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. Steve Geer Fermilab April 23 rd, 2007 page 2

Motivation  We want to make it possible for the HEP community to build an affordable multi-TeV lepton collider.  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.  The Muon Collider concept is attractive because muons do not radiate as readily as electrons (m  / m e ~ 207): Steve Geer Fermilab April 23 rd, 2007 page 3  Present design work suggests that Muon Colliders with  s=3-5 TeV and luminosities O(10 34 ) cm -2 s -1 may one day be possible.

The Challenge  To produce sufficient luminosity for an interesting physics program (L = cm -2 s -1 at  s = 1-few TeV) will require very bright muon beams. This is challenging because:  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 ~10 21 muons/year !  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   Muons decay (t 0 = 2  s). Beam manipulation & acceleration must be rapid, and detector must be shielded. Steve Geer Fermilab April 23 rd, 2007 page 4

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 2-4 MW Proton Source Hg-Jet Target Decay Channel Helical Cooler Buncher Bunch Merger Ring Cooler(s) Final Cooler Pre Accel -erator Acceler- ation Collider ~ 4 km 3 TeV Steve Geer Fermilab April 23 rd, 2007 page 5

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 1-4 MW Proton Source Hg-Jet Target Decay Channel Linear Cooler Buncher Pre Accel -erator Acceleration Storage Ring ~ 1 km 5-10 GeV GeV GeV Steve Geer Fermilab April 23 rd, 2007 page 6

Neutrino Factory vs Muon Collider NFMC Proton BeamYesSame TargetYesSame Capture & DecayYesSame BuncherYesSame Phase RotationYesSame Early CoolingYesSame ? More CoolingNoYes Early AccelerationYesDifferent More AccelerationNoYes Storage RingYesDifferent DetectorYesDifferent Neutrino Factories & Muon Colliders are linked by their common R&D and possible staging path. Steve Geer Fermilab April 23 rd, 2007 page 7 Could be an 8 GeV H- linac delivering 2 MW … would need a rebunching ring to produce short (3ns) bunches.

Target Design  Targetry design + R&D is common to Neutrino Factories & Muon Colliders  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.  Targetry design developed in Neutrino Factory Studies 1 (in 2001) and 2 (in 2002): Target Station Design Target Station Schematic Steve Geer Fermilab April 23 rd, 2007 page 8

Liquid Hg Jet R&D 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. t = ms 2 ms 7 ms 18 ms 0 Tesla 13 Tesla 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. 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 Steve Geer Fermilab April 23 rd, 2007 page 9

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

Ionization Cooling  Muons decay (   = 2  s)  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 to evolve, but typically consist of a multi-Tesla solenoid lattice to confine the muons, low-Z absorbers, and NCRF cavities.  A m long channel like this is adequate for a NF (4D cooling). More technology needed for MC (6D Cooling)  Muons created within large phase-space volume. Beam cooling required before injecting into an accelerator. Cooling Channel Section Liq. H 2 RF Steve Geer Fermilab April 23 rd, 2007 page 11

MUCOOL Steve Geer Fermilab April 23 rd, 2007 page 12  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

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

MUCOOL Absorber R&D Steve Geer Fermilab April 23 rd, 2007 page 14  Liquid H 2 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 Absorber Design

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

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

ISS - IDS Steve Geer Fermilab April 23 rd, 2007 page 17 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)

ISS Result Steve Geer Fermilab April 23 rd, 2007 page 18 Store μ + & μ - simultaneously –10 21 muon decays/yr –E μ ~ 25 GeV  Now have an internationally agreed upon baseline design  Similar to Study 2a design  Up to and including the cooling compatible with our present baseline Muon Collider design

Beyond a Neutrino Factory Steve Geer Fermilab April 23 rd, 2007 page 19  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 will require 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.

Muon Collider Cooling Channel (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.  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  requires low 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(10 6 ). Steve Geer Fermilab April 23 rd, 2007 page 20

New Ideas & a New Initiative Steve Geer Fermilab April 23 rd, 2007 page 21  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 from Muons 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:

Muon Collider Task Force Steve Geer Fermilab April 23 rd, 2007 page 22 Muon Collider Advanced Accelerator R&D Proposal TASK FORCE 35 members MUONS INC. 5 collaborators BNL 6 collaborators LBNL 4 collaborators ANL 1 collaborator JLAB 5 collaborators

Proposed MCTF Activities – 1 Steve Geer Fermilab April 23 rd, 2007 page 23 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. 2.Component Development: We will develop and bench test the components needed for the 6D cooling channel. 3.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 MeV/c muons will be used in the 6D ionization cooling demonstration experiment.

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

Proposed MCTF Activities - 2 Steve Geer Fermilab April 23 rd, 2007 page 25 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 Cooling &MC DesignExperimental R&DMagnet R&D Cooling Design: -realistic modeling -simul 6DHCC exper -radiation/diagn/RF -inj/extr/transport -error sensitivity MTA studies: -build MTA p-line -beam dump -MTA infrastructure -200/800 cavity test -absorber LH,He/LiH 6D Cooling Expt: -design work -m-product’n/capture -m-transport/match -m-diagnostics -HCC cryo/PSs/QPS -beam dump/radiation -windows -absorber system HCC: -design -prototype/testing -fabrication/test HTS Solenoid: -material research -insert design -insert fabricat/test -solenoid design -prototype/test 12T Dipole: -specs -design -prototype/test

Staging Steve Geer Fermilab April 23 rd, 2007 page 26 There are several possibilities offering a flexible path to a multi-TeV muon 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

Summary Steve Geer Fermilab April 23 rd, 2007 page 27 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 ~ ) 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.

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