Download - 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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Page 1: 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

Page 2: 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 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)

25

0

25

16mz

Q1'

Q2'

Q3'

Q1'

Q2'

Q3'

Q1'

Q2'

Q3'Q1 Q2 Q3 B1 Solenoid

Vertical Half-width

(cm)

HorizontalHalf-width

(cm)

25

0

25

16mz

C2H4 'Proton absorber'

Acceptance ~ 0.4 milli-sterAn,x~0.25pi mm rad, An,y~0.03pi mm rad

Page 7: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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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.

Muon Transport, εn generation & Matching: - principles

Page 8: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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Muon Transport – TTL 7π,200MeV/c Solution

example for 7.1π mm rad case given above

Page 9: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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-> (p/moc)R.R' ~ εn, rms ~7.1π mm rad R/R'=2p/q ~ βmatch α ~ 0= αmatch

εn 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 ~ pref=208.6MeV/c

Page 10: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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Matched Turtle beam showing cooling in MICE. ε ┴

(m

rad

)P

z (M

eV

/c)

Z distance from centre of StepVI configuration

Page 11: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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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)

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

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.

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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)

Page 20: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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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

Page 21: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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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

Page 23: 1 MICE Beamline Design: General principles & expected capabilities Kevin Tilley, 16 th November Charge to beamline & desirable beam General principles.

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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

TOF0 3.221 1.500 1.591Ckov1 3.166 1.474 1.511

3.147 1.466TOF1 0.997 0.464 0.662Tracker1 0.957 0.446 0.634

0.957 0.446Good u+ 0.705 0.328 0.493

β┴ (tracker,stn4) 258mm 258mm 390mm

: - Using standard targeting assumptions: 1.7x1012 pot / second