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
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1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.
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MICE Beamline Design: General principles & expected capabilities
Kevin Tilley, 16th November
• Charge to beamline & desirable beam
• General principles & design (with reference to basic 7pi design)
• Pion Injection & Decay Section - Solution
• Muon Transport & εn Generation/Matching - Solution
• Status of current optics designs
• Expected capabilities
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MICE Muon Beam - Generic Needs
• Other important features:-
– High flux muon beam at MICE (good transmission)
– Single muons of either sign
• Charge:-
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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
• εn generation / matching
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MICE Beamline Design - General Solution
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Pion Injection & Decay Channel - principles
• For high energy muons -> high energy pions:-
Angle of beamline to ISIS as acute as possible (~25°) forhigh 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.
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Almost all emittance, momenta cases use same pion optic above. (only 1 envisaged exception – 10pi, 240MeV/c case)
C2H4 'Proton absorber'
C2H4 'Proton absorber'
C2H4 'Proton absorber'
Pion Injection & Decay Channel - Solution
Q1'
Q2'
Q3'Q1 Q2 Q3 B1 Solenoid
Vertical Half-width
(cm)
HorizontalHalf-width
(cm)
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0
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16mz
Q1'
Q2'
Q3'
Q1'
Q2'
Q3'
Q1'
Q2'
Q3'Q1 Q2 Q3 B1 Solenoid
Vertical Half-width
(cm)
HorizontalHalf-width
(cm)
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0
25
16mz
C2H4 'Proton absorber'
Acceptance ~ 0.4 milli-sterAn,x~0.25pi mm rad, An,y~0.03pi mm rad
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• 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, C2H4 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.
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)
Quantity
Emittance at tracker plane 3 (+/-10%~Ptot) ~8.44Beta at tracker plane3 (+/-10%~Ptot) ~0.3Alpha at tracker plane3 (+/-10%~Ptot) -
Momentum ref (imposed) 208.6dp/p (+/-10%) yes
Purity (evaluated in G4BL) Particle TOF1
π+ 1.29%
μ+ 97%
other 1.71%
Transmission >0.25%Rate (evaluated in G4BL) # ~ 328 good muons / sec
# assumes 1.7x1012 protons intersecting targetalso assumes rate in TOF0 is scaled to meet 1.5MHz
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Other designs
There are other optics design in place, with “nominal” boxes:-
p
Low Mid High
240
200 TT-8.4.mm rad (evaluates to 8.8 in G4BL)
TT-nom 10mm rad: Qmatch
G4BL ‘May’07 ~11mm rad. Q: match
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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.
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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?
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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 -> y3σ = 26.4cm
y_max aperture = 23.6cm hence beamsize for 6pi ≥ aperture.
Smaller emittances require larger yrms
So 6pi is ~ a lower limit.
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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.
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Expected capabilities – Momenta & purity
Looking at the extreme cases
p
1 6 10
240
200
140
1pi, 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 indecay 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)
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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 tomitigate 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
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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. Δytarget(max) ~ +/-5mm seems plausible.
- plan to estimate & measure typical misalignments offsets at MICE.
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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)
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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 VS
M1
/ H
SM
1
CK
V1
VS
M2
HS
M1
Q4-6 Q7-9TO
F0
TO
F1
Beam correction for -1mm displacement, 0mrad angle in H & V
Bea
m c
orre
ctio
n f
or
0 m
m
dis
pla
cem
en
t, 1
mra
d
an
gle
in H
an
d V
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~ 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 CK
V1
Q4-6 Q7-9TO
F0
TO
F1
~ 0.15m
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The full future lattice at the moment
If all of these systems are required, there are many devices between B2 – Q4
D2 VS
M1
/ H
SM
1
CK
V1
VS
M2
HS
M1
Q4-6 Q7-9TO
F0
TO
F1
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
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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 εn~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.
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• Backup Slides.
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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.
Original raw rates Reducing target Using Collimatorinsertion