Muon Capture for a Muon Collider David Neuffer

Muon Capture for a Muon Collider David Neuffer July 2009 1

0 utline Ø Motivation § μ+-μ- Collider front end Ø Produce, collect and cool as many muons as possible • Start with ν-Factory IDS design study § Reoptimize for Collider • Shorter bunch train § Higher energy capture, shorter front-end • Larger gradients Ø Beam Loss problem § Chicane, Absorber, shielding Ø Discussion 2

Muon Collider/NF Beam Preparation Ø Baseline Muon Collider beam preparation system similar to that for Neutrino Factory § downstream portions (6 D cooling, acceleration, collider) are distinct • much more cooling and acceleration needed for collider Neutrino Factory Muon Collider 3

IDS Baseline Buncher and φ-E Rotator Ø Drift (π→μ) Ø “Adiabatically” bunch beam first (weak 320 to 232 MHz rf) § P 0 = 233; PN=154 Me. V/c N=10 Ø Φ-E rotate bunches – align bunches to ~equal energies § 232 to 2022 MHz, 12 MV/m Ø Cool beam 201. 25 MHz p π→μ FE Tar get Solenoid 18. 9 m Drift ~60. 7 m Buncher ~33 m Rotator 42 m Cooler ~80 m 4

Neutrino Factory version Ø NF baseline version § Captures both µ+ and µ- 700 Me. V/c 0 m § ~0. 1 µ/p within IDS acceptance • εT < 0. 03, εL < 0. 15 0 Me. V/c Ø Basis for cost/design studies § rf requirements § Magnet requirements -30 m Drift - 80 m 30 m Bunch-110 m v Rotate-150 m 23 bunches Cool-240 m 5

Rf Buncher/Rotator/Cooler requirements Ø Buncher § § 37 cavities (13 frequencies) 13 power supplies (~1— 3 MW) Ø RF Rotator § § § 56 cavities (15 frequencies) 12 MV/m, 0. 5 m ~2. 5 MW (peak power) per cavity Ø Cooling System – 201. 25 MHz § 100 0. 5 m cavities (75 m cooler), 15 MV/m § ~4 MW /cavity rf Front End section Length #rf cavitie s frequenci es # of freq. rf gradient rf peak power requirements Buncher 33 m 37 319. 6 to 233. 6 13 4 to 7. 5 ~1 to 3. 5 MW/freq. Rotator 42 m 56 230. 2 to 202. 3 15 12 ~2. 5 MW/cavity Cooler 75 m 100 201. 25 MH z 1 15 MV/m ~4 MW/cavity ~240 m 193 29 ~1000 MV ~550 MW Total drift) Magnet Requirements: 6

Rf cavity Concept design construction operation 7

Toward Muon Collider Ø Bunch trains for NF - ~80 m § Best 23 bunches (~35 m) have ~75% of captured muons Ø Rf within magnetic field problem must be solved § § Pill box rf baseline Magnetic insulation Bucked-coil Gas-filled rf Ø Assume will be solved § µ+µ- Collider will improve to the next level of performance 8

Reoptimize for µ+µ- Collider Front End Ø Muon Collider front end optimum is somewhat different § Short bunch train preferred • Bunches are recombined later … § Maximum μ/bunch wanted § Longitudinal cooling included; may accept larger δp § Larger rf gradient can be used (? ) • • NF will debug gradient limits Cost is less constrained Ø For variant, we will have shorter BR system, more gradient, and capture at higher momentum § § 230 275 Me. V/c 150 m 120 m 9/12/15 MV/m 12. 5/15/18 or 15/18/20 MV/m 1. 5 T 2 T 9

High-frequency Buncher and φ-E Rotator Ø Drift (π→μ) Ø “Adiabatically” bunch beam first (weak 350 to 232 MHz rf) § P 0 = 280; PN=154 Me. V/c N=10 Ø Φ-E rotate bunches – align bunches to ~equal energies § 232 to 202 MHz, 15 MV/m Ø Cool beam 201. 25 MHz § 1. 2 cm Li H, 15 MV/m Ø Similar to Neutrino Factory p π→μ FE Tar get Solenoid 18. 9 m Drift ~40 m Buncher ~33 m Rotator 34 m Cooler ~80 m 10

Rotated version Ø End up with fewer, larger N, bunches § More μ/p ~ • 20 -40% more ? ? § Larger δp (larger εL/bunch) 15 bunches 11

Collider version Ø Has ~30% shorter train Ø More μ/p 1. 0 Ge. V/c § ~0. 15 μ/p (from ~0. 11) Ø Captures more of the “core” of the initial π/μ NEW MC § Rather than lower half of the core … 0 All at target IDS 12

Further iteration? Ø ΔN: 10 8 Ø Rf gradients: 12. 5 18 MV/m § Or 15 18 20 MV/m Ø Shorter system ~102 m p π→μ FE Tar get Solenoid 14. 05 m Drift ~33 m Buncher ~25. 5 m Rotator 27 m Cooler ~80 m 13

N=8 variant Ø Shorter bunch train 800 Me. V/c § But not that much • • 15 12 bunches Bunch phase space larger • Longitudinal cooling ? 0 εL/10 εT 0. 3 µ-/p . . . All µ 0. 2 0. 1 µ/p e. T <0. 03, e. L <. 3 0 50 100 150 200 14

Beam losses along Front End – half-full? Ø Start with 4 MW protons § End with ~50 k. W μ+ + μ- • • plus p, e, π, … ~20 W/m μ-decay • >0. 1 MW at z>50 m § ~0. 5 MW losses along transport Ø “Hands-on” low radiation areas if hadronic losses < 1 W/m § Booster, PSR criteria § Simulation has >~100 W/m • Drift Cool With no collimation, shielding, absorber strategy Ø Need more shielding, collimation, absorbers § Reduce uncontrolled losses § Special handling 15

Comments on Front End Losses Ø First ~70 m has 30 cm beam pipe within ~65 cm radius coils § ~30+ cm for shielding § Radiation that penetrates shielding is what counts … • p π→μ FE Tar Solenoid get 12. 7 m Drift ~60. 0 m Buncher ~33 m Rotator 42 m Cooler ~90 m < 1 W/m ? § Could the shielding handle most of the losses in the first ~70 m? Shielding ? Ø Major source is protons Protons after target 16

Comments on Losses Ø High energy Protons (>4 Ge. V) do not propagate far § 8 Ge. V lost in Beam dump Ø Large spectrum at lower energies § ~20 k. W; 1 Ge. V protons § significant number propagate down cooling channel § Losses at absorbers Ø Other than protons, most losses are μ’s and e’s from μ-decay § Less dangerous in terms of activation • > 1 W/m OK ? § μ’s would penetrate through more shielding Ø Some protons captured in “cooling rf buckets” § ~30/10000 § 2 Ge. V p 17

Chicane to remove high-energy p Ø C Rogers ( see also Gallardo/Kirk) suggests using Chicane to filter out unwanted p/e/ § Sample parameters • 5 m segments-10 coils 1. 25 /coil • Larger momenta >400─500 Me. V/c not accepted 18

Chicane removes high-energy particles Ø Single chicane works as well as double chicane (? ) § Offsets orbit Ø Works for both signs Ø Would remove most hadronic residual § Heats beam? <10% ? Ø But must absorb losses somehow … 19

Chicane Performance 20

Parameters of Proton Absorber Ø Absorbers reduce number of protons § Losses occur near absorber § Significant proton power remains Ø 10 cm C = 40 Me. V Ø Tried 1 to 4 cm Be § Similar localized losses § Less perturbation to cooling system 21

Comments Ø Muon Collider version is an incremental change from IDS § ~25 to 33% shorter § Higher gradients • 9/12/15 15/16/18 ? § Capture at ~275 Me. V/c rather than 230 Me. V/c Ø Collider optimum might be a further increment along … ? Ø Optimization should include initial cooling with 6 -D § Used only transverse in present study, Li. H absorbers (~1. 2 cm) 22

Summary Muon Accelerator Program 23