MICE Beamline Optics Design

1. MICE Beamline Optics Design • MICE Needs • Generic Solution • Pion Injection & Decay Section (a) Inputs (b) Solution • Muon Transport (a) Inputs (b) Solution • εn Generation/Matching (a) Inputs (b) Solution • Current & projected status. Kevin Tilley, RAL, 12th June

2. MICE Muon Beam - Generic Needs • MICE Generic Needs:- • High flux muon beam (>600 muons thru-going MICE lattice / msec ) • High purity muon beam ( < 0.1 % contamination) • Muon momenta ~ 140 - 240 MeV/c • Muon emittances ~ 1 π mm rad - 10 π mm rad. • Beam matched into MICE Lattice • Also:- • Desirable muon momentum spread of at least dp/p=+/-10% full width.

3. MICE Beamline Design - General Solution • General Solution:- • Many similar requirements to Condensed Matter Pion-Muon Decay beamlines:- • PSI uE4 • TRIUMF muon beamlines • RAL-RIKEN muon beamline • Thus we adopted to design a pion-muon decay beamline. • For us, demark into 4 functions: - • pion injection • decay • muon transport • εn generation / matching

4. MICE Beamline Design - General Solution

5. MICE Beamline Design - General Solution • Codes: TRANSPORT / DECAY TURTLE : • Why? • Since both codes had extensive history / support. • Both codes had been used to design all aforementioned pion-muon decay channels:- • PSI uE4 • TRIUMF muon beamlines • RAL-RIKEN muon beamline • How used? • Pion injection & decay channel:- • Straightforward use of 2nd order TRANSPORT • Muon transport • Muon source comes from DECAY TURTLE • Optical design using TRANSPORT to both:- • fit to desired conditions • sometime fit and find 'difference' for driving TTL to desired conditions. • Always iteration between TTL / TPT until rqd conditions met (as seen in Turtle) • Pb. diffuser • Thickness set from scattering seen in DECAY TURTLE (uses REVMOC) • Beamline materials (except Pb) • Modelling consistently in both codes with same Δp as G4Beamline but free

6. Pion Injection & Decay Channel - Inputs/Constraints • Geometry:- • Target - Beamline Angle of ~20° chosen to allow high energy pion capture. • Hence Target to Q1 centre shortest is 3.0m due to proximity to Synchrotron • Hole Drilled ! (April 2004) • z-position :- to avoid old HEP tunnel ? • - to avoid Synchrotron electrical junction box • Hence length of pion injection fixed, at Target - B1 centre ~ 7.98m • B1 – Decay Sol distance set since Decay Sol to fit wall-hole geometry (hole ≈ 650mm)

7. Pion Injection & Decay Channel - Solution • Flux:- • Maximise # pions into decay section -> maximises useful muon flux @ MICE • normally length (fixed) • magnets (limited) • optics • Maximise accumulation of muons in decay section • highest decay solenoid field, consistent with controllable beam profile. • Purity :- • Chose always ~ highest pion momenta possible - to allow selection of 'backward' going muons for higher purity & higher fluxes. (Risk is assumption of accurate modelling of pion spectrum from target, but Target test in October'06 may tell us answer?):- • Inclusion of C2H4 'proton absorber' (ranges out protons < ~ 500MeV/c) -> greatly aids purity

8. Pion Injection & Decay Channel - Solution C2H4 'Proton absorber' C2H4 'Proton absorber' C2H4 'Proton absorber' C2H4 'Proton absorber' Almost all emittance, momenta cases use same pion optic above. (1 envisaged exception)

9. Pion Injection & Decay Channel - Solution 58.8 % 58.8 % 58.8 % 58.8 % 146086 146086 46836 • Comparison with RAL-RIKEN pion injection & decay channel:- • Compares fairly well with RAL-RIKEN:- Injection efficiency ~ 0.82 RIKEN Efficiency of accumulating muons ~ 0.66 RIKEN (even though we have longer distance to Q1, longer quads, smaller aperture quads, and a longer pion injection than the RAL-RIKEN beamline. Also solenoid is shorter!) • The pion injection & decay channel geometry & optic have remained unchanged since ~ CM8 in April 2004 :- under many different emittance and momentum designs. Sole changes have been scaling the fields of Q1-Q3, B1 & Decay Solenoid. May require small change for 10π,240MeV/c case

10. Muon Transport, εn generation & Matching: - Inputs/Constraints • To provide beam for emittance generation & matching. • Sufficient to deliver wide range of matched emittances into MICE. • To include PID detectors & TOF0 – TOF1 Min Sepn 6.11m (deemed sufficient at CM9 for 6π / 200MeV/c case). • Presence of upstream iron detector shield -> Q9 downstream mirror plate – Start / End Coil 1.1 distance no closer than 550.8mm. • Not required to be achromatic but dispersion should be "small" ! (VC Jan 12 04!)

11. Muon Transport, εn generation & Matching: - Solution • Flux:- • Aimed at keeping B2 - Q4 distance as small as possible to capture maximum muon solid angle • Aimed at keeping beamline length short to minimise beamsize growth due to PID detectors. • Aimed at positioning PID detectors near beam foci to minimise emittance blowup. (both of the above competitive with keeping a minimum TOF0-TOF1 separation.) • Purity:- • Selection of backward going muons. • Matching:- • Scheme described in more detail in later slide, but:- • Focus beam with a beamsize a function of desired emittance • Triplet lattice, in order to facilitate:- ie. focus and same beamsize both planes at MICE • Perform emittance generation immediately before MICE. Possible beam transport correction schemes.

12. Muon Transport - Solution example for 7.1π mm rad case given above

13. εn generation & matching into MICE - Solution • The scheme. Place Pb Diffuser at MICE End Coil 1.1 -> (p/moc)R.R'= εn, rms R/R'=2p/qB= βmatchα=0= αmatch

14. εn generation & matching into MICE - Solution Example from 6π mm rad, 200MeV/c attempt Xrms ~ 3.55 cm , x’rms = 107 mrad , rxx'=0.04 yrms ~ 3.61 cm , y’rms = 102 mrad ryy'=0.13 -> (p/moc)R.R' ~ εn, rms ~7.1π mm rad R/R'=2p/q ~ βmatchα ~ 0= αmatch Example achieves ~ matched 7.1π mm rad

15. Current & projected status. Red = dubious (without collimation) Green = projected to be possible • Designs in TRANSPORT/TURTLE