1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles & design (with reference to basic 7pi design) Pion Injection & Decay Section - Solution Muon Transport & ε n Generation/Matching - Solution Status of current optics designs Expected capabilities

2 2 MICE Muon Beam - Generic Needs Other important features:- –High flux muon beam at MICE (good transmission) –Single muons of either sign Charge:-

3 3 MICE Beamline Design – General Principles & Solution General Solution:- –We adopted to design a pion-muon decay beamline. –since many requirements similar to Condensed Matter pion-muon decay beamlines:- PSI uE4 TRIUMF muon beamlines RAL-RIKEN muon beamline –For our particular case, beamline spilts into 4 parts: - pion capture decay muon transport ε n generation / matching

4 4 MICE Beamline Design - General Solution

5 5 Pion Injection & Decay Channel - principles For high energy muons -> high energy pions:- Angle of beamline to ISIS as acute as possible (~25°) for high energy pions. B1 large such that B2 small & low dispersion. For fluxes:- Optics set to capture maximum acceptance & maximise transmission into decay solenoid. Target tp Q1 fixed by angle choice (3m) Pion capture capture length fixed at ~8m given entry to MICE hall & RF junction box. Maximise accumulation of muons in decay section –highest decay solenoid field, consistent with controllable pion beam profile. For high purities Chose always ~ highest pion momenta possible - to allow selection of 'backward' going muons for higher purity & higher fluxes.

6 6 Almost all emittance, momenta cases use same pion optic above. (only 1 envisaged exception – 10pi, 240MeV/c case) C2H4 'Proton absorber' Pion Injection & Decay Channel - Solution C2H4 'Proton absorber' Acceptance ~ 0.4 milli-ster A n,x ~0.25pi mm rad, A n,y ~0.03pi mm rad

7 7 For large Momentum spreads:- B2 angle small for small dispersion. Triplets. For high flux:-- B2 - Q4 distance small as possible. Beamline short. PIDs near focal points. For high purity:- Choose backward decay muons, C 2 H 4 on B2. To produce high emittances & match into MICE – focus/scatter beam at end. Cartoon:- Described in more detail later, but:- Perform emittance generation immediately before MICE. Focus beamsize at diffuser. Muon Transport, ε n generation & Matching: - principles

8 8 Muon Transport – TTL 7π,200MeV/c Solution example for 7.1π mm rad case given above

9 9 -> (p/m o c)R.R' ~ ε n, rms ~7.1π mm rad R/R'=2p/q ~ β match α ~ 0= α match ε n generation & matching into MICE – TTL 7π,200MeV/c Soln. Xrms ~ 3.55 cm, x’rms = 107 mrad, rxx'=0.04 yrms ~ 3.61 cm, y’rms = 102 mrad ryy'=0.13 …for +/-10% momentum cut ~ p ref =208.6MeV/c

10 Matched Turtle beam showing cooling in MICE. ε ┴ (m rad) Pz (MeV/c) Z distance from centre of StepVI configuration

11 Status of this particular optics design The TTL 7π,200MeV/c case has received closer study in Turtle & also evaluation in the G4Beamline code -> with air, improved scattering model, spatially extended dipole fringes etc, optics design evaluates to ~8.4pi in TTL. -> there is some disagreement with G4Beamline (HN talk)

12 Other designs There are other optics design in place, with “nominal” boxes:- pp LowMidHigh TT-8.4 . mm rad (evaluates to 8.8  in G4BL) TT-nom 10  mm rad: Qmatch G4BL ‘May’07 ~11  mm rad. Q: match 140 Plan: Use single design “TTL-8.4  ” as starting point for commissioning in January – best understood. Continue to aim towards theoretical optics for other 200MeV/c cases.

13 Expected capabilities Filling out the “matrix” of (  p) case’s is ongoing. Q: what theoretically is the matched emittance range? Q: what momentum range is furnishable ? Q: what are the beam purities likely to be? Q: what is the dp/p spread and match at different momenta? Q: what are likely misalignments at MICE? Q: what are likely Rates?

14 Expected capabilities - Emittances Minimum emittance From Turtle, natural unmatched emittance exiting TOF1 is~ 2.8 pi mm rad. (smaller than G4BL) ie. -> ~ 1.4 pi mm rad unnormalised. Estimate of minimum emittance beam that can be matched:- given 2.8 mm rad, to produce 6pi requires:- lead thickness = 7.5mm alpha ~ 0.23, beta ~ 0.78m before lead. (MA talk) We can propagate optics functions back to Q9 & Q8 & est. beamsize At Q8 centre -> y 3σ = 26.4cm y_max aperture = 23.6cm hence beamsize for 6pi ≥ aperture. Smaller emittances require larger y rms So 6pi is ~ a lower limit.

15 Expected capabilities - Emittances To produce matched emittances < ~6pi:- If from beamline:- - use a collimator either upstream of Q7 or downstream of Q9 - move Q9,Q8,Q7 ~ 0.8m closer to MICE. If in software:- - offline select particles with smaller emittances Maximum emittance Larger matched emittances require smaller y_rms in Q8/Q9, hence not limited by apertures. Limited only by thickness’ of lead available – no known limits in beamline.

16 Expected capabilities – Momenta & purity Looking at the extreme cases pp 11 66 10  pi, 140MeV/c requires 0mm lead –> requires-> ~210MeV/c muons in decay solenoid.. -> Requires from initial pion momenta of at least 210MeV/c. 10pi, 240MeV/c requires ~15mm lead -> requires ~ 310MeV/c muons in decay solenoid. -> Requires from initial pion momenta of at least 310MeV/c. Pion momentas 60 – 550MeV/c available from the target. Upstream beamline can transport up to 486MeV/c pions. Can supply all required momenta to MICE. For all (  p) cases except (10pi, 240MeV/c), can choose pion momenta such that muon momenta from backward decay. Purities of ~97% expected for all settings except (10pi,240MeV/c)

17 Expected capabilities – dp/p In all cases, can deliver +/-10% dp/p about the reference momentum (red lines) Quality of match over +/-10% dp/p:- The scattering through thick lead diffuser helps to mitigate chromatic aberrations. Makes phase space-ellipses more upright α->0, & provides momentum dependent scattering for β=2p/qB. For high emittance cases (≥7π) we should expect match over reasonable momentum bite. Indications shown: for +/-10% beam:-> Full distribution is what MICE will see, with rms ~13.4% % dp/p

18 Expected capabilities – control of alignment Some misalignment of the beam at MICE is expected, due to:- - intrinsic nature of particle source – need to change the target position to change beam rate. Δy target (max) ~ +/-5mm seems plausible. - plan to estimate & measure typical misalignments offsets at MICE.

19 Expected capabilities – misalignment tolerances We have a reasonable estimate of acceptable misalignments:- - on the basis of minimal reweighting, & cooling reduction. ( 1mm – 2mm x & y offset & ~3mrad offset in x’ & y’ in spectrometer solenoid1) - these translate into alignment criteria at TOF1 – near end of beamline – coordinates within red ellipse:- ~ dx ~ 5mm, dx’ ~ 1mrad)

20 Beam line Steering – baseline scheme If required, correctors could be placed at ~ 310°/98° (H/V position) and ~ 221/160° (H/V angle) phase advance upstream of tracker input plane. B2 VSM1 / HSM1 CKV1 VSM2 HSM1 Q4-6 Q7-9 TOF0 TOF1 Beam correction for -1mm displacement, 0mrad angle in H & V Beam correction for 0 mm displacement, 1 mrad angle in H and V

21 ~ 0.57m Expected capabilities – Rates & TOF0 collimator The beam rates at MICE can be limited for a number of reasons:- - Few proton intersections on target (ISIS beam loss activation etc) - If target rates are reasonable, a limiting factor can be the beam intensity at TOF0 detector, which cannot operate above 1.5MHz. - Instead of restricting target dip, can collimate ‘outlier particles’ not reaching MICE but contributing to TOF0 rate. Hence incr intensities. - Will not install on day1, but if required, have baseline solution:- B2 CKV1 Q4-6 Q7-9 TOF0 TOF1 ~ 0.15m

22 The full future lattice at the moment If all of these systems are required, there are many devices between B2 – Q4 D2 VSM1 / HSM1 CKV1 VSM2 HSM1 Q4-6 Q7-9 TOF0 TOF1 A second solution for steering magnets is to steer using trim coils on the quadrupoles. This needs to be simulated. A number of other options are possible for collimator (shorter length/distributed) ~ 0.57m ~ 0.15m Beamline monitor

23 Summary. Outlined general principles & solution. Status of designs:- have starting optic for January. Study further for commissioning. Produce further (  p) Expected capabilities: - lattice can furnish down to ε n ~6pi - 1pi requires collimation All required momenta can be supplied. Large dp/p can be matched. Muon purity >97% for all cases except (10pi, 240MeV/c) Steering correction scheme if beam alignments are outside tolerances. Collimation solution if TOF0 intensity limits rates at MICE.

24 Backup Slides.

25 TOF0 nominal rates & collimation example : - Shows benefit to MICE of collimator: 50% increase in rate :- Is inserted quite far (as per example here). :- this does effect rates & optical properties of beam at the end. :- Would need use case plan: may need to retune optics if adopt this approach. : - Using standard targeting assumptions: 1.7x10 12 pot / second