1 of 13 Stephen Brooks / RAL / March 2005 Muon Front Ends Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory and Muon Collider

Stephen Brooks / RAL / March

20051 of 13

Muon Front Ends

Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory

and Muon Collider


20052 of 13

Contents

• Future Accelerator Projects Requiring Muon Front Ends– Neutrino Factory– Muon Collider

• Choice of Particle – why Muons?• Front End Components and Options• Context: National R&D Programme

– UK Neutrino Factory (UKNF) group


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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


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• p+ + + e+e

• Uses 4-5MW proton driver– Could be based on ISIS


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• “Front end” is the muon capture system


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The Muon Collider

• Goal: to push the energy frontier in the lepton sector after the linear collider

• p+ +,− +,−

+

-

3+3TeV MuonCollider Ring


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Why Collide Muons?Particle Proton Electron MuonMass 938 MeV 0.511 MeV 106 MeVSynchrotron radiation limit (LEP-II RF)

28.5 TeV 0.102 TeV 5.55 TeV

Machine issues

B-field limit at 7 TeV (LHC)

Linear 1 TeV collider more cost-effective Half-life of

2.2 sPhysics problems

Messy collisions None


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Design Challenges

• Must accelerate muons quickly, before they decay– Conventional synchrotrons cycle too slow– Once is high, you have a little 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


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Muon Front End Components

• Targetry, produces pions (±)• Pion to muon decay channel

– Uses a series of wide-bore solenoids• “Phase rotation” systems

– Outside scope of this talk• Muon ionisation cooling (as in “MICE”)

– Expensive components, re-use in cooling ring• Muon acceleration (RLAs vs. FFAGs)


200510 of 13

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


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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 Rees 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…


200512 of 13

The Decay Channel (ctd.)

• Developed a more accurate code, Muon1• 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!


200513 of 13

UKNF Research Efforts

• MICE at RAL (phase I~2007; II~2009-10)• FFAG electron model at Daresbury

– Under definition!• Target shock studies program• Beamline design and optimisation work

– Myself, Grahame (+ new recruit soon)– Network with European “BENE” collaboration

• http://hepunx.rl.ac.uk/uknf/

http://hepunx.rl.ac.uk/uknf/




200514 of 13

BACKUP!

In case the time is longer than my slides.

Web report

http://stephenbrooks.org/ral/report/2003-1


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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


200516 of 13

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


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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


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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 RodLength (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


200519 of 13

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


200520 of 13

Optimised Design for the Decay Channel (137 parameters)

0

5

10

15

20

25

Fiel

d (T

esla

)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Size

(met

res)

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)


200521 of 13

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


200522 of 13

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

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1 of 13 Stephen Brooks / RAL / March 2005 Muon Front Ends Providing High-Intensity, Low-Emittance Muon Beams for the Neutrino Factory and Muon Collider