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Bunched-Beam Phase Rotation for a Neutrino Factory David Neuffer, Andreas Van Ginneken, Daniel Elvira Fermilab
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2 Outline Study I – II -Factory – feasible but too expensive Remove Induction Linac Replace with High-Frequency Buncher and phase-energy rotation: Capture beam in high-frequency buckets Reduce energy spread with high-frequency E rotation Inject into fixed-frequency cooling Simulation and Optimization Simucool – adds transverse motion + some optimization DPGeant – fully realistic simulation; match into realistic cooling Discussion Cost estimates ??? Future development
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3 Study 2 Costs …. “Cost” reduced by ~25% from Study I
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4 Induction Linac Technology Study II scenario uses ~ 250m long induction linac to capture muons. Cost is prohibitive Technology is difficult
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5 System Overview Drift (100m) – decay and drift Buncher (60m) 300 187MHz, V 4.8 (z/L) 2 MV Trap beam into string of ~200 MHz bunches E Rotator(8.4m) 187MHz, V = 10 MV/m rotate string of bunches to ~ equal energies Cooler (100m) 183MHz – ionization cooling
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6 Longitudinal Motion Through System Drift Bunch E rotate Cool
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7 SIMUCOOL Beam at end of buncher
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8 Simucool-optimized buncher and fixed frequency E rotation Obtains ~0.28 /p at end of buncher
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9 Simucool optimizations (AvG) Large statistics tracking code ( SIMUCOOL ) can be used to reoptimize Buncher + E Rotation Reoptimize baseline adiabatic buncher and fixed frequency E rotation (track rms bunches in each band) – Obtains ~0.3 /p (up from 0.25) Change fixed-frequency to “vernier”; sets phase to N-1/2 wavelengths from first to last ref. bunch; maximizes E rotation - obtains ~0.35 /p Retrack with ICOOL – similar results are obtained
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10 “Vernier”-optimized E rotation Obtains ~0.34 /p at end of buncher
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11 Latest Optimizations A van Ginneken has completed a new set of optimizations; changes some parameters Drift – reduced to ~76m Buncher parameters changed: Reference energies: 64 MeV; 186MeV 20 bunches between reference energies 384 233 MHz Linear ramp in voltage 0 to 6.5MV/m Still 60m long Rotator changed “vernier” frequency (20 + ) wavelengths between reference bunches (234 220 MHz), 10MV/m Optimize on longitudinal bunch densities Best case has 0.16 Longer Rotator (~30m)
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12 System Components (new version) Drift (80m) Buncher (60m) 380 230 MHz, V 6.5 (z/L) MV/m E Rotator(30m) 230 220 MHz, V = 10 MV/m Cooler (100m) ~220 MHz
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13 Bunching and Rotation Beam after drift plus adiabatic buncher – Beam is formed into string of ~ 200MHz bunches Beam after ~200MHz rf rotation; Beam is formed into string of equal-energy bunches; matched to cooling rf acceptance
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14 DPGeant simulations (D. Elvira) Fully “realistic” transverse and longitudinal fields Magnetic fields formed by current coils Rf fields from pillbox cavities (within solenoidal coils Studied varying number of different rf cavities in Buncher (60 (1/m) to 20 to 10) … 20 was “better”, 10 only a bit worse Simulations of -E rotation Will extend simulations + optimization through cooling channel
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15 Beam at end of drift
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16 Beam at end of Buncher 64.9 % of the particles survive at the end of the buncher
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17 DP Geant results – rf rotation First rf rotation with DPGeant
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18 Hardware For Adiabatic Buncher Transverse focussing ( currently) B=1.25T solenoidal focusing R=0.30m transport for beam Rf requirements: Buncher: ~300 ~200 MHz; 0.1 4.8MV/m (60m) (initially 1 cavity every 1m; reduces frequency in 2-4MHZ steps; 1-D and other early simulations indicate ~10 frequencies are sufficient (~10MHz intervals) Rotator: 230 220 MHz; 10MV/m (~10m)
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19 RF requirements for High-frequency buncher and phase rotation Rf frequencyVoltage (Quadratic to Linear ramp) 300 MHz0.075 - 1 MV - 6m 290 MHz0.675 - 4 MV - 6m 280 MHz1.875 - 7 MV - 6m 270 MHz3.675 - 10 MV - 6m 260 MHz6.08 - 13 MV - 6m 250 MHz9.08 - 16 MV - 6m 240 MHz12.7 - 19 MV - 6m 230 MHz16.9 - 22 MV - 6m 220 MHz21.7 - 25 MV - 6m 210 MHz Buncher: 28 MV - 6m ( Total rf voltage: 101 to 145 MV) 200 MHz100 MV (10m) - Rotator
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20 Rf Cost Estimate (Moretti) FrequencyCavity lengthCavity CostRf PowerTotal 300MHz0.5 m225 k$ 450k$ 2901450350800 28029007001600 270290010001900 260290010001900 250290010001900 240290010001900 2303120015002700 2204140015002900 2105180020003800 20010380042008000 33.5m133751447527850k$
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21 Transport requirements Baseline example has 1.25 T solenoid for entire transport (drift + buncher + rf rotation) (~170m) Uncooled -beam requires 30cm radius transport (100m drift with 30cm IR – 1.25T) In simulations, solenoid coils are wrapped outside rf cavities. (~70m 1.25T magnet with 65cm IR) FODO (quad) transport could also be used …
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22 Cost of Solenoid (PDG handbook) Stored Energy: Cost: Combine 2 solenoids: 3.5 + 7.9 = 11.4 M$ Multiply by ~2 ~20 M$ ? (D. Summers can do Al solenoids for ~10 M$)
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23 Cost of magnets (M. Green) 100m drift: 11.9 M$ (based on study 2) Buncher and phase rotation: 26 M$ (study 2) Cryosystem: 1.5M$; Power supplies 0.5M$ Total Magnet System : 40M$
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24 $$ Cost Savings ?? High Frequency - E Rotation replaces Study 2: Decay length (20m, 5M$) Induction Linacs + minicool (350m, 320M$) Buncher (50m, 70M$) Replaces with: Drift (100m) Buncher (60m) Rf Rotator (10m) Rf cost =30M$; magnet cost =40M$ Conv. Fac. 10M$ Misc. 10M$ …… Back of the envelope: (400M$ ?? 100M$ )
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25 Summary High-frequency Buncher and E Rotation simpler and cheaper than induction linac system Performance probably not as good as study 2, But System will capture both signs ( +, - ) To do: Complete simulations with match into cooling channel! Optimizations Scenario reoptimization
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26 Energy projection
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