Muon Cooling for a Neutrino Factory Rolland P. Johnson Muons, Inc. ( muonsinc/ )

1. m Muons, Inc. Muon Cooling for a Neutrino Factory Rolland P. Johnson Muons, Inc. (http://www.muonsinc.com/) More muon cooling in NF designs would improve synergy between NF and MC R&D. Present designs of MC front-ends would fill NF storage rings very well. 6D muon cooling progress has been encouraging. It may well be ready for prime time when a NF is to be built. NuFact09

2. m Muons, Inc. Muons, Inc. Scenario for:High-Energy High-Luminosity Muon Colliders • precision lepton machines at the energy frontier • achieved in physics-motivated stages that require developing inventions and technology, e.g. • intense proton driver (CW Linac, H- Source, Laser Stripping) • stopping muon beams (HCC, EEX w Homogeneous absorber) • neutrino factory (HCC with HPRF, RLA in CW Proj-X) • Z’ factory (low Luminosity collider, HE RLA) • Higgs factory (extreme cooling, low beta, super-detectors) • Energy-frontier muon collider (more cooling, lower beta) NuFact09

3. m Muons, Inc. LEMC Scenario Bogacz Dogbones Scheme NuFact09

4. m Muons, Inc. NF from MC front end While many aspects of MC and NF R&D are shared, muon beam cooling is an exception. In the present ISS NF scheme, relatively little transverse and no longitudinal muon cooling is required, while MC plans require at least 6 orders of magnitude 6-D cooling. MC front-ends (p-driver, target, collection, cooling, acceleration to 30 GeV) are well-suited to fill a NF storage ring, with good duty factor and high intensity. The smaller emittance due to muon cooling can reduce the cost and difficulty of the RF and magnet systems of the NF. The incorporation of more cooling into NF designs can lead to better cooperation and faster progress for both machines. A CW 8-GeV proton driver could provide sufficient beam power to do both simultaneously. Recent muon cooling progress is very encouraging. Yonehara slides from LEMC09 follow: NuFact09

5. Muons, Inc. Progress of Helical Cooling Channel Design K. Yonehara APC, Fermilab LEMC’09 @ Fermilab, K. Yonehara 1

6. Work on HCC project Muons, Inc. Speakers in this workshop A. Tollestrup, M. Chung • Test high pressure RF cavity • Study RF incorporating into helical magnet • Improve cooling performance • Cooling factor & Transmission efficiency • Phase space matching • Design 6D cooling demo experiment M. Lopez, M. Popovic R. Abram, S. Kahn LEMC’09 @ Fermilab, K. Yonehara 2

7. Optimization of HCC Muons, Inc. • In past, mainly optimized helical magnet • Adjust dispersion function • Cooling decrements • Momentum slip factor • In present, take into account RF parameters • Increase longitudinal acceptance LEMC’09 @ Fermilab, K. Yonehara 3

8. Clue: How to tune RF parameter Muons, Inc. • HCC has sufficient size of transverse • phase space acceptance • HCC acceptance is limited by • longitudinal phase space Increase longitudinal acceptance by increasing RF bucket LEMC’09 @ Fermilab, K. Yonehara 4

9. RF bucket dependence Muons, Inc. v = 400 MHz, κ=1.0, λ=1.0 m GH2 pressure = 200 atm (at room temp) Old design New design E = 31.4343 MV/m, ψ=160˚, Lrf = 100 mm E = 16.0 MV/m, ψ=140˚, Lrf = 50 mm ΔE [GeV] ΔE [GeV] Transmission efficiency is improved by more than factor two LEMC’09 @ Fermilab, K. Yonehara 5

10. Transverse motion Muons, Inc. E = 31.4343 MV/m, ψ=160˚, Lrf = 100 mm E = 16.0 MV/m, ψ=140˚, Lrf = 50 mm Particle loss LEMC’09 @ Fermilab, K. Yonehara 6

11. Six-Dimensional emittance evolution in new HCC Muons, Inc. v = 400 MHz, κ=1.0, λ=1.0 m GH2 pressure = 200 atm (at room temp) Old result Cooling factor > 500 ~ 29 @ z = 100 m LEMC’09 @ Fermilab, K. Yonehara 7

12. Transverse vs Longitudinal phase space Muons, Inc. 1035 1034 1033 1032 Lo Emit Hi Emit 400 MHz 800 MHz REMEX 200 MHz 1600 MHz 400 MHz 800 MHz equi. emit 1600 MHz (E)PIC • A 400 MHz HCC may be sufficient to accept the beam phase space • after conventional frontend channel • If Luminosity estimation is correct we can reach 1034 even only HCC • section (but reverse emittance exchange is still needed) 8

13. Parameter list Muons, Inc. Field parameter Average momentum = 0.25 GeV/c GH2 pressure = 200 atm @ room temp Dispersion factor = = 1.83 Length of each channel = 100 m HCC field can be produced with correction magnets (although it is not a final design) RF cell RF length will be double to save RF power For instance, 400 MHz HCC, Lrf = 200 mm, Erf = 40 MV/m LEMC’09 @ Fermilab, K. Yonehara 9

14. High Pressure RF for HCC Muons, Inc. HPRF can be operated in strong magnetic fields We do not know how HPRF works under high rad condition Dopant gas will reduce electron density in the cavity LEMC’09 @ Fermilab, K. Yonehara 10

15. HPRF simulation Muons, Inc. LEMC’09 @ Fermilab, K. Yonehara 11

16. RF system in HCC Muons, Inc. Second design First design Traveling wave RF system Lrf = 50 mm, 400 MHz helical RF Required RF power is ~2.5 GW/m!! The reason is that it has a coupling hole only at the center of cell window By putting a magnetic coupling holes on side of cell, required power is SIGNIFICANTLY reduced down to ~40 MW/m Field quality is also good (but it has a thin metallic window) LEMC’09 @ Fermilab, K. Yonehara 12

17. Wedge shape RF system Muons, Inc. L. Thorndahl tried further challenge! He designs a wedge shape RF system Advantage: Reduce peak E field Probably, reduce number of cells Challenge: Asymmetric field distribution LEMC’09 @ Fermilab, K. Yonehara 13

18. Dielectric loaded RF Muons, Inc. Cu/Steel ceramics Vaccum/H/He LEMC’09 @ Fermilab, K. Yonehara 14

19. Possible way to put RF power Muons, Inc. RF power coupling port LEMC’09 @ Fermilab, K. Yonehara 15

20. Next-to-do Muons, Inc. • More tuning up • Design matching section • Study RF power issue • Push high pressurizing RF cavity test harder • Propose dielectric loaded RF test • Mechanical design of HCC LEMC’09 @ Fermilab, K. Yonehara 16

21. Conclusion Muons, Inc. • A 400 MHz HCC can be a first cooling • Achieve luminosity 1034 even without extra cooling channel • but emittance exchange is still needed • High pressure RF with dopant gas seems ok • HPRF with beam is crucial • Need to study RF power issue • Dielectric loaded RF test LEMC’09 @ Fermilab, K. Yonehara 17