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MCTF Scenario Update

MCTF Scenario Update. Y. Alexahin (FNAL). 2 nd Muon Collider Design workshop, JLab, Newport News VA December 8-12, 2008. Parameters of Different MC options. Low Emit. High Emit. MCTF07 MCTF08  s (TeV) 1.5 Av. Luminosity (10 34 /cm 2 /s) * 2.7 1 1.33-2

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MCTF Scenario Update

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  1. MCTF Scenario Update Y. Alexahin (FNAL) 2nd Muon Collider Design workshop, JLab, Newport News VA December 8-12, 2008

  2. Parameters of Different MC options Low Emit. High Emit. MCTF07 MCTF08 s (TeV) 1.5 Av. Luminosity (1034/cm2/s) * 2.7 1 1.33-2 Av. Bending field (T) 10 6 6 Mean radius (m) 361.4 500 500  495 No. of IPs 4 2 2 Proton Driver Rep Rate (Hz) 65 13 40-60 Beam-beam parameter/IP 0.052 0.087 0.1 * (cm) 0.5 1 1 Bunch length (cm) 0.5 1 1 No. bunches / beam 10 1 1 No. muons/bunch (1011) 1 20 11.3 Norm. Trans. Emit. (m) 2.1 25 12.3 Energy spread (%) 1 0.1 0.2 Norm. long. Emit. (m) 0.35 0.07 0.14 Total RF voltage (GV) at 800MHz 407103c 0.21** 0.84**  0.3† Muon survival N/N0 0.31 0.07 0.2 ? + in collision / proton 0.047 0.01 0.03 ? 8 GeV proton beam power 3.62*** 3.2 1.9-2.8 ? --------------------------------------------------------------------------- *) Luminosity calculated taking account of the hour-glass factor but ignoring the dynamic beta effect. **) Momentum compaction in the present ring design c=1.510-4. Note that it would be better to assume f=1.3GHz to keep the RF voltage at a reasonable level (0.52GV for MCTF07 set) ***) Assumes  /p ratio of 0.15 after capture and precooling, and only decay losses afterwards. Positive and negative muons are assumed to be produced independently (from different protons). †) The latest ring design has c=5.510-5. Voltage for HE option is now 75MV MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

  3. Medium Emittance scheme of 2007 bunch coalescing new Fernow or PIC 201 MHz FOFO snake • Bob Palmer found a number of weak points with this scheme: • bunch length grows >1m during REMEX in 50T solenoids  bunch frequency of 200MHz can not be sustained  merging should be done before REMEX with all the losses due to merging and recooling; • “super-Fernow” (aka bucked coil) lattice has poor transmission (<50%) making the overall survival a dismal 4% (if Guggenheims are used for 6D cooling). • Still I think that the idea is not hopeless, though modifications are necessary MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

  4. Cooling in 50T solenoids (R.Palmer) • If using “Super-Fernow” lattice to achieve =12 microns then final ||=40 mm/bunch : • 4 bunches can merged at high energy to stay within ||<160 mm, • final ||=40 mm/bunch  z= 40 mm/3%=1.34m  f_bunch<50MHz, e.g. 40MHz  groups by 5 bunches can be merged and recooled at low energy • so the total of 20 bunches can be merged together in 2 steps • Is there any sense in merging at both low and high energy? • Where are we intensity-wise? MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

  5. Estimated losses vs 6D emittance (R.Palmer) Taking just 12 bunches for merging gives overall capture/rotation/precooling efficiency ~0.08mu+/ 8GeV p (D.Neuffer), according to my estimates (may be wrong) this will increase required p-driver power for HE scheme to 6MW Besides that, losses due to merging and recooling seem too low - looks like we are in deep trouble anyway MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

  6. Muon distribution after capture/rotation (D.Neuffer) momentum [GeV/c] particles / bucket total efficiency 0.38 +/ 8GeV p bucket #1 time [s] bucket # integral intensity • Increase in the number of bunches from 10 to 20 gives ~38% increase in number of muons • Merging by groups of 5 bunches will require less recooling  will reduce losses during merging and recooling • Possible intensity related problems alleviated bucket # 2995 particles in the first 10 buckets, 1136 in the next 10 MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

  7. Bucked coil lattice (“Super-Fernow”) simulations 400MHz RF cavities, 28MV/m p=100MeV/c  Bmax=17T main solenoids (opposite polarity) transmission w/o decay bucking coils LiH absorbers (0.75cm wide) 80cm period # (cm) J||(cm) J(cm) (min) = 0.76cm   N=41m x 1.08=44m (equilibrium) DA: 2 J/ N ~3 sigma is marginal MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

  8. Possible solutions • All attempts to improve bucked lattice DA failed: it has strong innate nonlinearities: • by virtue of Maxwell’s equations • Possible solutions: • taper the bucked lattice so that its acceptance followed the beam emittance, • wait for Rol and Yaroslav to develop their PIC lattice, • develop lattice with magnetic insulation of RF cavities instead (Bob’s favorite) • or just alternating FOFO lattice in the 2nd passband: diverging magnetic field probably will reduce accelerating gradient by only 20% (20MV/m  16MV/m in the 200MHz case) whereas the RF packing factor will significantly increase  total gain in cooling rate • What are the prospects of the Medium Emittance scheme in more general? MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

  9. Emittances & Transmission in HE/ME schemes stage N (mm) ||N (mm) transmission High emittance option RF capture/rotation 20 40 - 4D cooling in linear channel 12 40 0.7 201/402 MHz RFOFO 1.4 1.4 0.45 bunch merging 1.4 21×1.4= 30 0.8 201/402 MHz RFOFO 1.4 5 ? 804 MHz RFOFO 0.38 1.2 0.55 50T solenoids 0.025 65 0.7 Acceleration 0.025 65 0.7 total= 0.068 MCTF scenario RF capture/rotation 20 40 - 201 MHz FOFO snake 3 5 0.85* + 402/804 MHz HCC 0.7 0.5 0.9* Fernow channel (PIC?) 0.07 0.5 0.5(?)  (?) 50T solenoids 0.012 14 0.85 Acceleration (total) 0.012 - 0.7 bunch merging 0.012 140 0.85 total= 0.19 ---------------------------------------- *) Critically depends on success with HPRF N protons/bunch ~ 1012/ 0.15/ 0.19 = 3.5 ×1013 at 8GeV MCTF Scenario - Y. Alexahin MCD workshop, BNL December 4, 2007

  10. Developments and Plans • On the negative side: • Merging at low energy is unavoidable • Still no satisfactory PIC lattice (?) • On the positive side: • Merging twice (at low and high energy) allows to capture more muons/proton • “Super-Fernow” may have much better transmission if tapered • 200 MHz snake really works, has a large throat! • Upgraded collider ring lattices satisfies both ME and HE (marginally) requirements • A lot of new ideas! • Near-term plans: • combine bunch rotation with initial 6D cooling in 200 MHz snake • helical snake for final 6D cooling • HCC with block solenoids • 50 T solenoid channel with matching/RF MCTF Scenario Update - Y. Alexahin 2nd MCD workshop, JLab, December 9, 2008

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