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1 Front End Capture/Phase Rotation & Cooling Studies David Neuffer Cary Yoshikawa December 2008
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20utline Introduction ν-Factory Front end Capture and Φ-E rotation High Frequency buncher/rotation Study 2B ν-Factory Shorter version ν-Factory →μ + -μ - Collider Discussion
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3 Variations tried … Study 2A – ISS baseline Shorter bunch train example n B = 10 Better for Collider; as good for ν-Factory ICOOL/G4Beamline simulations Study of “accepted” particles Rf cavities in solenoids? Use “magnetic insulation” ASOL lattice Not too bad Variations Higher energy capture ??
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4 Study2B June 2004 scenario (ISS) Drift –110.7m Bunch -51m (1/ ) =0.008 12 rf freq., 110MV 330 MHz 230MHz -E Rotate – 54m – (416MV total) 15 rf freq. 230 202 MHz P 1 = 280, P 2 = 154 N V = 18.032 Match and cool (80m) 0.75 m cells, 0.02m LiH Captures both μ + and μ - ~0.2 μ/(24 GeV p)
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5 Study 2B ICOOL simulation (N B =18) s = 1m s=109 m s=166m s= 216m -40 60 500 MeV/c 0 Drift Bunch Rotate 500 MeV/c 0
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6 Features/Flaws of Study 2B Front End Fairly long system ~300m long (217 in B/R) Produces long trains of ~200 MHz bunches ~80m long (~50 bunches) Transverse cooling is ~2½ in x and y, no longitudinal cooling Initial Cooling is relatively weak ? - Requires rf within magnetic fields in current lattice, rf design; 12 MV/m at B = ~2T, 200MHz MTA/MICE experiments to determine if practical For Collider (Palmer) Select peak 21 bunches Recombine after cooling ~1/2 lost -4060m 500 MeV/c
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7 Shorter Bunch train example Reduce drift, buncher, rotator to get shorter bunch train: 217m ⇒ 125m 57m drift, 31m buncher, 36m rotator Rf voltages up to 15MV/m (×2/3) Obtains ~0.26 μ/p 24 in ref. acceptance Slightly better ? ~0.24 μ/p for Study 2B baseline 80+ m bunchtrain reduced to < 50m Δn: 18 -> 10 -3040m 500MeV/c
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8 Further iteration/optimization Match to 201.25 MHz cooling channel Reoptimize phase, frequency f = 201.25 MHz, φ = 30º, Obtain shorter bunch train Choose ~best 12 bunches ~ 21 bunch train for Collider at N B = 18 case ~12 bunches (~18m) ~0.2 μ/p ref in best 12 bunches Densest bunches are ~twice as dense as N B = 18 case
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9 Details of ICOOL model (N B =10) Drift– 56.4m B=2T Bunch- 31.5m P ref,1 =280MeV/c, P ref,2 =154 MeV/c, n rf = 10 V rf 0 to 15MV/m (0.5m rf, 0.25m drift) cells 360 MHz 240MHz -E Rotate – 36m – V rf = 15MV/m (0.5m rf, 0.25m drift) cells N V = 10.07 (240 -> 201.5 MHz) Match and cool (80m) Old ICOOL transverse match to ASOL (should redo) P ref = 220MeV/c, f rf = 201.25 MHz 0.75 m cells, 0.02m LiH, 0.5m rf, 16.00MV/m, φ rf =30° Better cooling possible (H 2, stronger focussing)
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10 Simulations (N B =10) -30m 30m 500 MeV/c 0 Drift and Bunch s = 89 m s = 1m Rotate s = 125 m s = 219 m Cool
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11 Front end simulations Initial beam is 8GeV protons, 1ns bunch length
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12 Comparisons of ICOOL and G4BL Simulations of front end and cooling agree ICOOL and G4Beamline results can be matched Buncher – rotator – cooler sequence can be developed in both codes Method Captures both μ + and μ - But some differences dE/dx is larger in ICOOL Phasing of rf cavities uses different model
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13 12.9 m43.5 m31.5 m36 m driftbuncher rotator capture MC Front End Layout in G4beamline “Cool and Match” 3 m (4x75 cm cells)“Cool” 90 m of 75 cm cells Rotator 36 m long 75 cm cell 1 cm LiH 23 cm vacuum 50 cm 201.25 MHz RF cavity
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14 G4BeamlineICOOL Pi+/Mu+ Pi-/Mu- Rotator End
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15 G4BeamlineICOOL Pi+/Mu+ Pi-/Mu- Cool End
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16 Reduce number of independent frequencies Initial example had different rf frequency for each cavity Buncher- 42 cavities -31.5m 360to 240 MHz Rotator- 48 cavities -36m 240 to 202 MHz Reduce # by 1/3 14 in buncher; 16 in rotator Nearly as good capture (<5%less) Similar to study 2B discreteness Reduce by 1/6 7 in buncher, 8 in rotator Significantly worse (~20%)
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17 Accepted particles Accepted particles fit final beam cuts: A X + A y < 0.03m A L < 0.2m Initial beam has momenta from ~75 to ~600 MeV/c Final beam is ~200 to 300 MeV/c Transverse emittance is cooled from ~0.014 to ~0.0036 600 MeV/c 0 MeV/c
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18 Accepted Longitudinal distros 1m 135m 196m -30m 40m 600 MeV/c 0 MeV/c
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19 “Accepted” Beam properties For study 2A acceptance means several cuts: A X + A y < 0.03m A L < 0.2m For beam within acceptances, ε t, N,rms = 0.0036m (from ~0.007) ε L, N,rms = ~0.04m (from ~0.09) Emittances are much smaller than the full-beam emittances … x rms = 6cm (all-beam) x rms = 3.6cm (accepted-beam) -30cm +30cm -30cm +30cm
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20 Variations - focusing Buncher and Rotator have rf within 2T fields Field too strong for rf field ?? Axial field within “pill-box” cavities Solutions ?? Open-cell cavities ?? “magnetically insulated” cavities Alternating Solenoid lattice is approximately magnetically insulated Use ASOL throughout buncher/rotator/cooler Use gas-filled rf cavities ASOL lattice
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21 Use ASOL lattice rather than 2T Study 2A ASOL B max = 2.8T, β * =0.7m, P min = 81MeV/c 2T for initial drift Low energy beam is lost (P < 100MeV/c) Bunch train is truncated OK for collider Also tried weaker focusing ASOL B max = 1.83T, β * =1.1m, P max = 54 MeV/c 1.33 T for initial drift Match scaled from 2A match + - B(z)
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22 2T -> ASOL
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23ASOL-1.33T 56m 62m 133m 193m
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24 First ASOL results Simulation results 2.8T ASOL 0.18 μ/24 GeV p 0.059 μ/8 GeV p Cools to 0.0075m 1.8T ASOL 0.198 μ/24 GeV p 0.064 μ/8 GeV p ~10% more than stronger focussing Cools to 0.0085m Baseline (2T -> ASOL) had ~0.25 μ/24 GeV p ~0.08 μ/8 GeV p Weaker-focusing ASOL has ~10% better acceptance than 2.8T lattice Longer bunch train
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25 Variant-capture at 0.28 GeV/c 0.0 1.0GeV/c 0.0 2T → 2.8T ASOL -30m+40m-30m+40m 1.0GeV/c s=59m s=66m s=126m s=200m
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26 Capture at 280 MeV/c Captures more muons than 220 MeV/c For 2.T -> 2.8T lattice But in larger phase space area Less cooling for given dE/ds Δs Better for collider Shorter, more dense bunch train If followed by longitudinal cooling 220 MeV/c 280 MeV/c
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27 Higher-Energy Simulation results Higher energy capture improves capture for high- field lattice Cooling is slower Not as good for low-field lattice Weaker focusing reduces cooling For High field lattice: 2.8T ASOL 8GeV beam 0.065 μ/p in ε t <0.03, ε L <0.2 0.093 μ/p in ε t <0.045, ε L <0.3 24 GeV beam 0.19 μ/p in ε t <0.03, ε L <0.2 0.26 μ/p in ε t <0.045, ε L <0.3 For Low-field lattice 1.8T ASOL 8GeV beam 0.053 μ/p in ε t <0.03, ε L <0.2 0.083 μ/p in ε t <0.045, ε L <0.3 cools only to ~0.010m
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28Discussion High frequency phase-energy rotation + cooling has been explored Shorter system better for Collider Shorter bunch train; denser bunches “magnetic insulated” lattice could be used rather than B = 2 or 1.75 T lattice Slightly worse performance (?) ~10 to 20% worse for neutrino factory Ok for Collider Particles lost are at end of bunch train
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29 Any Questions?
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30 Project X Status
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31 High-frequency Buncher and φ-E Rotator Form bunches first Φ-E rotate bunches
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