stephen brooks / ral / april 2004 muon front ends providing high-intensity, low-emittance muon beams...
TRANSCRIPT
Stephen Brooks / RAL / April
2004
Muon Front Ends
Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory
and Muon Collider
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
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
Stephen Brooks / RAL / April
2004
The Neutrino Factory
• p+ + + e+e
• Uses 4-5MW proton driver– Could be based on ISIS
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 MuonCollider Ring
Stephen Brooks / RAL / April
2004
Why Collide Muons?
Particle Proton Electron Muon
Mass 938 MeV 511 keV 106 MeVSynchrotron radiation limit (LEP-II RF)
28.5 TeV 102 GeV 5.55 TeV
Same length of 100MV/m L.C. 1.33 TeV 1.33 TeV 1.33 TeV
Bending field limit (LHC) 7 TeV 7 TeV 7 TeV
ProblemsMessy collisions
NoneHalf-life of 2.2 s
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
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)
Stephen Brooks / RAL / April
2004
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…
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: <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!
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
Stephen Brooks / RAL / April
2004
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…
Stephen Brooks / RAL / April
2004
BACKUP!
In case the time is longer than my slides.
Web report
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
Stephen Brooks / RAL / April
2004
NuFact Intensity Goals
• “Success” is 1021 /yr in the storage ring
Proton Energy/GeV Intensity/MW Target eff (pi/p) MuEnd eff (mu/pi) Operational mu/year in storage ring Current/uA
8 4 20% 1.0% 30% 5.90497E+19 500 "Not great" scenario
8 1 60% 2.0% 35% 1.03337E+20 125 ISIS MW only to reach 10^20
8 5 60% 3.5% 40% 1.03337E+21 625 "Quite good" 5MW scenario (gets 10^21)
8 5 1.75 8.5% 55% 1.00646E+22 625 Required to reach 10^22
1.75 = PtO2 target inclined at 200mrad, see Mokhov FNAL PiTargets paper 20% = 2.2GeV dataset from Paul Drumm
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
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
Stephen Brooks / RAL / April
2004
Decay Channel Lattice
Drifts Length (m)
D1 0.5718 [0.5,1]
D2+ 0.5 [0.5,1]
Solenoids Field (T) Radius (m) Length (m)
S120
[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
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
Stephen Brooks / RAL / April
2004
Optimised Design for the Decay Channel (137 parameters)
0
5
10
15
20
25
Fie
ld (
Te
sla
)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Siz
e (
me
tre
s)
Solenoid Field Solenoid Radius Solenoid Length Drift Length
•Maximum Length
•Minimum Drift
•Maximum Aperture
•Maximum Field
(not before S6)
(mostly)
(except near ends)
(except S4, S6)
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
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
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Length
Radius
0.463 m
0.402−0.003n m