Muon Front Ends

Stephen Brooks / RAL / April

2004

Muon Front Ends

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

and Muon Collider


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


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


2004

The Neutrino Factory

• p+ + + e+e

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


2004

The Muon Collider

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

• p+ +,− +,−

+

-

3+3TeV MuonCollider Ring


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


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


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)


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…


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!


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


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…


2004

BACKUP!

In case the time is longer than my slides.

Web report


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


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


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


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


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


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


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)


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


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

Muon Front Ends

Documents

Transcript of Muon Front Ends