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20-50 GeV Muon Storage Rings

20-50 GeV Muon Storage Rings. C. Johnstone and G. Rees MuTAC Meeting Fermilab March 16, 2006. Introduction: Muon Storage Rings for a Neutrino Factory. Neutrino beam/ Storage Ring energies 20 and 50 ( max ) GeV Production Straight Muon beam divergence* 0.1/   0.2/ 

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20-50 GeV Muon Storage Rings

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  1. 20-50 GeV Muon Storage Rings C. Johnstone and G. Rees MuTAC Meeting Fermilab March 16, 2006

  2. Introduction: Muon Storage Rings for a Neutrino Factory • Neutrino beam/ Storage Ring energies 20 and 50 (max) GeV • Production Straight • Muon beam divergence*0.1/   0.2/  • Muon beam normalized emittance* 30,000 mm-mrad (95%) • Momentum acceptance 1% Note these two parameters dictate beam size in production straight • Peak magnetic field (assume NBTi SC) ~7T • Declination angle: 3 and 7x103 km detector ~10 and 36 • Bunch train length 400nsec (120 m) Overiding design Goal: • maximize muon decays in production straight or ratio of production straight(s)/circumference *small compared to neutrino beam divergence, rms ~1/ *assumes minimal, mainly transverse cooling

  3. Storage Ring Designs • Racetrack • 1 long production straight; 1 detector site • Supports both charge species of muon beams circulating in opposite directions (if opposing straights are identical) • Isosceles Triangle Ring • 2 production straights per muon species; 2 detector sites • Supports only one charge species • Would require reversing polarity of ring, or • Two rings (current proposal) one stacked above the other

  4. Feasibility I : U.S. Neutrino Factory Storage ring designs - site specific • 50 GeV Fermilab Storage Ring: racetrack • 13 declination angle • circumference, C = 1753 m • 39% ratio (1 prod str./C) Design predicated on ~6T SC arc dipoles

  5. Feasibility II : U.S. Neutrino Factory Storage ring designs - site specific • 20 GeV BNL Storage Ring: racetrack • 10 declination angle • C = 358 m • 35% ratio Design predicated on ~7T SC arc dipoles- (hence the short circumference achieved at 20 GeV)

  6. Site concerns for 7 & 3 x103 km detectors 7000 km 36 6000 km • Vertical depth (arcs << straights): • Racetrack: • Isosceles triangle: • Conclusion: relative depths of two similar circumference -triangular or racetrack - storage rings are very close surface 10 to 3 km site 46 36 to 7 km site

  7. 20 and 50 GeV Current Design Overview 20 and 50 GeV lattice ring designs complete Arc: FODO cells with ~6T dipole fields: 72 arc cells, combined-function magnets (triangle, for now) 90 arc cells, separated-function, tunable magnets (racetrack design, for now) Combined dispersion suppressor and matching sections Designed for MW intensities - warm bores of SC Clad with Pb (absorbs 80% of e beam power) 1 cm of W @50 GeV will also sufficiently protect SC coils Production straight design: SC solenoids - minimize beam size NC, 30 cm -bore quadrupoles - confines cryogenics to arcs Permanent magnet ~30 cm bore quads appear feasible Background sweep dipoles at ends of production straights

  8. 20  50 GeV upgrade; present status • Isosceles: • modify lattice + some magnet changes required; realignment • Muon/neutrino beam divergence fixed to 1/  at both energies • Racetrack: • no changes: 50 GeV ring installed and can be operated @20 GeV; • bores accommodate 20 GeV beam and increased internal shielding @50 GeV • Muon beam rms divergence increases from 0.1/ @20 GeV to 0.2/ @50 GeV These approaches are not specific to storage ring shape

  9. Triangular Muon Storage Ring ≥ 22.43° Neutrinos Neutrinos ± injections End bend Collimation, rf and tune change Designs for 20 and 50 GeV to fit in same tunnel now 50° to 60° C.Prior UKNF talk

  10. Racetrack Storage Ring Ring operates at 20 and 50 GeV – Arc dipoles powered at 2.5 and 6.3 T Background sweep dipoles at end of each straight Neutrinos  ± injections Neutrinos

  11. Muon Decay and Storage Ring Near Detector Muon Decay Ring (muons decay to neutrinos) To Far Detector 1 R109 To Far Detector 2 Neutrino Factory Far Detector 1 Far Detector 2 • Leaning towards a triangular shape with two baseline experiments • Racetrack shape also being pursued

  12. Potential dual far/near detector locations 12 # detector locations Apex angle of storage ring triangle C. Prior, 1/25/06 ISS scoping study

  13. Global Storage Ring Parameters PARAMETER TRIANGLE RACETRACK 20 : 50 GEV 20 : 50 GEV Circumference 1273 m 1371 m Production straight 2x~265 m (2x~21%) 496 m (36%) acceptance, normalized, 95% 4.8 mm-mrad (30) same (beam emittance) rms prod divergence 0.10/ : 0.12/  0.12/ : 0.19/  Global Tune, x / y 10.79 / 11.15 : 10.44 / 10.64 10.23 / 9.24 xmax/ymax 117 m : 184 m 155 m / 167 m Peak Field arcs 6.4T 6.3T Peak Field prod straight 4.3T : 6.4T* 0.2T** * solenoids ** quadrupoles

  14. Magnetic components: • Racetrack: • Magnets, in particular SC arc magnets, will resemble design in feasibility I study – see figures below • Triangle • Vertical mounting of SC elements in vertical return arc looks difficult • Should look at this aspect asap Dipole (left) and cryostat design (right) for racetrack, Feasibility I Study

  15. 20 GeV Lattice Functions for Triangular Ring (Excluding Production Straights)

  16. 20/50 GeV Lattice for Racetrack Ring Production Straight

  17. Discussion Issues • Number of bunch trains from n=1 @15 Hz to n=5 @50 Hz (80 bunches, 5 ns intervals with trains separated by 100 ns) • Reduces beam loading power levels by a factor of 50/3 to levels experienced in SNS • Vertical depth  circumference  # bunch trains •  operation • Separate rings for  stacked one above the other • Interleave bunch trains – doubles the circumference of each ring • Reverse polarity of triangular ring or racetrack • Use opposite straight in racetrack • Simultaneous  beams are under discussion in racetrack • Again doubles circumference or halves number of bunch trains/species

  18. General concerns • Emittance measurements: • Cannot be made accurately with a parallel beam – parameters multiply each other are ~ unchanging in prod. region • Cerenkov gas + windows may be disruptive in a ring; large effect @20 GeV on a parallel beam • Special straight needs to be designed for emittance measurements : expect 5% measurement of divergence which is a combination of resolution and profile recognition • Injection is difficult in a production-optics straight •  injected simultaneously • consider reversing polarity of ring? • Vertical orientation and mounting of SC magnets in triangular ring mechanically challenging? • Fringe fields • Tracking • Specialty insertion for aberrations from sextupoles+fringe fields • Can use return straight in racetrack; harder in triangle lattice

  19. Recommendations for Future Work • Survey of potential detector sites with angular ranges covered by triangular and racetrack storage rings, respectively – preliminary survey done • Kicker and Abort system and beam gaps, interleaving – under discussion • Chromatic correction (sextupoles) in triangular ring • Momentum acceptance and matching to FFAG accelerators • Mechanical design for vertical mounting of SC magnets • Design and comparison of injection • In production straight • Optimized “opposing” straight in racetrack • Emittance measurement design and accuracy • Tracking with fringe fields

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