1.  Stephen Brooks / RAL / April 2004 Muon Front Ends Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory and Muon Collider

2.  Stephen Brooks / RAL / April 2004 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.  Stephen Brooks / RAL / April 2004 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.  Stephen Brooks / RAL / April 2004 The Neutrino Factory p +   +   +  e + e  Uses 4-5MW proton driver –Could be based on ISIS

5.  Stephen Brooks / RAL / April 2004 The Muon Collider Goal: to push the energy frontier in the lepton sector after the linear collider p +   +,  −   +,  −  +-+- 3+3TeV Muon Collider Ring

6.  Stephen Brooks / RAL / April 2004 Why Collide Muons? ParticleProtonElectronMuon Mass938 MeV511 keV106 MeV Synchrotron radiation limit (LEP-II RF) 28.5 TeV102 GeV5.55 TeV Same length of 100MV/m L.C. 1.33 TeV Bending field limit (LHC) 7 TeV Problems Messy collisions None Half-life of 2.2  s

7.  Stephen Brooks / RAL / April 2004 Design Challenges Must accelerate muons quickly, before they decay –Synchrotron acceleration is too slow –But once  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.  Stephen Brooks / RAL / April 2004 Muon Front End Components Targetry, produces pions (  ± ) Pion to muon decay channel –Uses a series of wide-bore solenoids “Phase rotation” systems –Aim for either low  E or short bunch length Muon ionisation cooling (as in “MICE”) –Expensive components, re-use in cooling ring Muon acceleration (RLAs vs. FFAGs)

9.  Stephen Brooks / RAL / April 2004 The Decay Channel Has to deal with the “beam” coming from the pion sourcepion 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.  Stephen Brooks / RAL / April 2004 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: 0.5m drifts, etc. –Increased transmission to 9.6% Increased in the older code (PARMILA) too –Fixed a problem in the original design!

11.  Stephen Brooks / RAL / April 2004 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.  Stephen Brooks / RAL / April 2004 RAL Design for Cooling Ring 10-20 turns Uses H 2 (l) or graphite absorbers Cooling in all 3 planes 16% emittance loss per turn (probably) Tracking and optimisation later this year…

13.  Stephen Brooks / RAL / April 2004 BACKUP! In case the time is longer than my slides. Web report

14.  Stephen Brooks / RAL / April 2004 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.  Stephen Brooks / RAL / April 2004 NuFact Intensity Goals “Success” is 10 21   /yr in the storage ring Proton Energy/GeVIntensity/MWTarget eff (pi/p)MuEnd eff (mu/pi)Operationalmu/year in storage ringCurrent/uA 8420%1.0%30% 5.90497E+19500 "Not great" scenario 8160%2.0%35% 1.03337E+20125 ISIS MW only to reach 10^20 8560%3.5%40% 1.03337E+21625 "Quite good" 5MW scenario (gets 10^21) 851.758.5%55% 1.00646E+22625 Required to reach 10^22 1.75 = PtO2 target inclined at 200mrad, see Mokhov FNAL PiTargets paper20% = 2.2GeV dataset from Paul Drumm

16.  Stephen Brooks / RAL / April 2004 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.  Stephen Brooks / RAL / April 2004 The Decay Channel Has to deal with the “beam” coming from the pion source Evolution of pions from 2.2GeV proton beam on tantalum rod target

18.  Stephen Brooks / RAL / April 2004 Decay Channel Lattice Drifts Length (m) D10.5718 [0.5,1] D2+0.5 [0.5,1] Solenoids Field (T)Radius (m)Length (m) S1 20 [0,20] 0.1 [fixed] 0.4066 [0.2,0.45] S2-4 −3.3, 4, −3.3 [-5,5] 0.3 [0.1,0.4] 0.4 [0.2,0.6] S5-S24 ±3.3 (alternating) [-4,4] S25+ 0.15 [0.1,0.4] Final (S34)0.15 [fixed] 12 parameters –Solenoids alternated in field strength and narrowed according to a pattern 137 parameters –Varied everything individually Tantalum Rod Length (m)0.2 [fixed] Radius (m)0.01 [fixed] Angle (radians)0.1 [0,0.5] Z displacement (m) from S1 start 0.2033 (S1 centred) [0,0.45] Original parameters / Optimisation ranges

19.  Stephen Brooks / RAL / April 2004 Improved Transmission Decay channel: –Original design: 3.1%  + out per  + from rod –12-parameter optimisation  6.5%  + /  + 1.88% through chicane –137 parameters  9.6%  + /  + 2.24% through chicane Re-optimised for chicane transmission: –Original design got 1.13% –12 parameters  1.93% –137 parameters  2.41% 3`700`000 runs so far 1`900`000 runs 330`000 runs

20.  Stephen Brooks / RAL / April 2004 Optimised Design for the Decay Channel (137 parameters) Maximum Length Minimum Drift Maximum Aperture Maximum Field (not before S6) (mostly) (except near ends) (except S4, S6)

21.  Stephen Brooks / RAL / April 2004 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 FODO lattice FOFO lattice

22.  Stephen Brooks / RAL / April 2004 Design Optimised for Transmission Through Chicane Nontrivial optimum found Preferred length? Narrowing can only be due to nonlinear end-fields