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 energies20 and 50 (max) GeV  Production Straight  Muon beam divergence*0.1/   0.2/   Muon beam normalized emittance*30,000  mm-mr (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 7 km far detector~10  and 36   Bunch train length400nsec (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 600FeetRing Vertical Drop 10FeetTunnel ceiling to floor 10FeetShielding above ring 50FeetUndisturbed bottom layer of Galena Platteville 10FeetFor uncertainties in the above three numbers 680FeetTotal from Surface to Bottom of Galena Platteville

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 x10 3 km detectors  Vertical depth (arcs << straights):  Racetrack:  Isosceles triangle:  Conclusion: relative depths of two similar circumference - triangular or racetrack - storage rings are very close 6000 km 7000 km 36  to 3 km site 10  surface 36  46  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 Neutrinos  ± injections Collimation, rf and tune change End bend ≥ 22.43° Designs for 20 and 50 GeV to fit in same tunnel C.Prior UKNF talk now 50 ° to 60°

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

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

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

13. Global Storage Ring Parameters PARAMETER TRIANGLERACETRACK PARAMETER TRIANGLERACETRACK 20 : 50 GEV 20 : 50 GEV 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: 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 arclooks 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

20. 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

21. 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