1	Muon Front Ends Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory and Muon Collider
2	Contents Future Accelerator Projects Requiring Muon Front Ends Neutrino Factory Muon Collider Choice of Particle – why Muons? Design Components and Options Research Currently Underway By both Grahame Rees and myself
3	The Neutrino Factory Goal: To fire a focussed beam of neutrinos through the interior of the Earth What’s the point? Constrains post-Standard Model physics But why does this involve muons? Neutrinos appear only as decay products Decaying an intense, high-speed beam of muons produces collimated neutrinos
4	The Neutrino Factory p⁺ à p⁺ à m⁺ à e⁺n_en_m Uses 4-5MW proton driver Could be based on ISIS
5	The Muon Collider Goal: to push the energy frontier in the lepton sector after the linear collider p⁺ à p⁺,p⁻ à m⁺,m⁻à
6	Why Collide Muons?
7	Design Challenges Must accelerate muons quickly, before they decay Synchrotron acceleration is too slow But once g is high, you have more time High emittance of pions from the target Use an accelerator with a really big aperture? Or try beam cooling (emittance reduction) In reality, do some of both
8	Muon Front End Components Targetry, produces pions (p^±) Pion to muon decay channel Uses a series of wide-bore solenoids “Phase rotation” systems Aim for either low DE or short bunch length Muon ionisation cooling (as in “MICE”) Expensive components, re-use in cooling ring Muon acceleration (RLAs vs. FFAGs)
9	The Decay Channel Has to deal with the “beam” coming from the pion source Pion half-life is 18ns or 12m at 200MeV So make the decay channel about 30m long Grahame designed an initial version Used S/C solenoids to get a large aperture and high field (3T mostly, 20T around target) Needed a better tracking code…
10	The Decay Channel (ctd.) Developed a more accurate code Used it to validate Grahame’s design… 3.1% of the pions/muons were captured …and parameter search for the optimum Within constraints: <4T field, >0.5m drifts, etc. Increased transmission to 9.6% Increased in the older code (PARMILA) too Fixed a problem in the original design!
11	Two Phase Rotation Options Chicane (2001) FFAG-style magnets Shortens the bunch Have optimised matching 2.4% net transmission No cooling? 31.4MHz RF (2003) Reduces the energy spread 180±75MeV to ±23MeV Feeds into cooling ring
12	RAL Design for Cooling Ring 10-20 turns Uses H₂(l) or graphite absorbers Cooling in all 3 planes 16% emittance loss per turn (probably) Tracking and optimisation later this year…
13	BACKUP! In case the time is longer than my slides.
14	Muon Acceleration Options Accelerators must have a large aperture Few turns (or linear) in low energy part, so muons don’t decay Recirculating Linacs (RLAs, studied first) FFAGs (cyclotron-like devices) Grahame is playing with isochronous ones
15	NuFact Intensity Goals “Success” is 10²¹ m⁺/yr in the storage ring
16	Tracking & Optimisation System Distributed Computing ~450GHz of processing power Can test millions of designs Genetic Algorithms Optimisation good up to 137 parameters… Accelerator design-range specification language Includes “C” interpreter
17	The Decay Channel Has to deal with the “beam” coming from the pion source
18	Decay Channel Lattice 12 parameters Solenoids alternated in field strength and narrowed according to a pattern 137 parameters Varied everything individually
19	Improved Transmission Decay channel: Original design: 3.1% m⁺ out per p⁺ from rod 12-parameter optimisation à 6.5% m⁺/p⁺ 1.88% through chicane 137 parameters à 9.6% m⁺/p⁺ 2.24% through chicane Re-optimised for chicane transmission: Original design got 1.13% 12 parameters à 1.93% 137 parameters à 2.41%
20	Optimised Design for the Decay Channel (137 parameters)
21	Why did it make all the solenoid fields have the same sign? Original design had alternating (FODO) solenoids Optimiser independently chose a FOFO lattice Has to do with the stability of off-energy particles
22	Design Optimised for Transmission Through Chicane Nontrivial optimum found Preferred length? Narrowing can only be due to nonlinear end-fields