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The M2 beam for COMPASS. L.Gatignon / AB-ATB-EA. General layout and basic principles of the muon beam Optics and collimation of the muon beam Operational and performance issues – rate, halo Access related issues Other beam modes – hadron and electron beams Documentation.

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The m2 beam for compass

The M2 beam for COMPASS

L.Gatignon / AB-ATB-EA

  • General layout and basic principles of the muon beam

  • Optics and collimation of the muon beam

  • Operational and performance issues – rate, halo

  • Access related issues

  • Other beam modes – hadron and electron beams

  • Documentation

The M2 beam line for COMPASS


The m2 beam for compass

Merge of two proposals:

HMC – muon physics

CHEOPS – hadron spectroscopy

Trigger-hodoscopes

μ Filter

160 GeVμ

ECal & HCal

SciFi

SM2

RICH

MWPC

SM1

6LiD Target

Gems

Straws

Silicon

Drift chambers

Micromegas

COMPASS (M2-BEAM)

Two stage spectrometer

Polarized beam andtarget

~75% ≥50%

SAT,

LAT,

PID

≈ 250 physicists from 28 institutes

The M2 beam line for COMPASS


The m2 beam for compass

CHEOPS:

Each has:

  • a target

  • 2 magnets

  • lots of tracking

  • 2 RICH

  • 2 HCAL

  • 2 ECAL

  • 25 MCHF cost

HMC:

One detector

Swap beams

COMPASS

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

COMPASS Spectrometer Layout

The M2 beam line for COMPASS


Compass beam requirements

COMPASS BEAM REQUIREMENTS

  • The beam serves sometimes as a muon beam, sometimes as a hadron beam. An electron calibration beam should be available from time to time as well.

  • The muon beam spot size at the COMPASS target should be smaller than 8 mm RMS in each plane, with a RMS divergence not exceeding 1 mrad,

  • The muon beam intensity at 160 GeV/c should be at least2 108 muons per SPS cycle.

  • The horizontal angle of incidence on the COMPASS polarised target is variable to allow compensation of the 1.05 Tm dipole field in that target,

  • The hadron beam will transport secondary hadron beams up to 280 GeV/c,

  • Particle identification should be done with 2 CEDAR counters, for which a 15 metres long parallel section is required,

  • The hadron beam should have a spot size of not more than 3 mm RMS and a small divergence,

  • The hadron intensity can be as high as 108 particles per SPS cycle.

  • The electron beam intensity should be several 104 electrons per burst at 40 GeV/c

2006: Concentrate on muon beam running. Only tests with e- and hadron beams

The M2 beam line for COMPASS


The m2 beam for compass

Muons from pion decay

  • Pion decay in p center of mass:

m

(p*, E*)

mp2 – mm2

q*

p* = = 30 MeV/c

2 mp

n

mp2 + mm2

E* = = 110 MeV/c

2 mp

m

  • Boost to laboratory frame:

Em = gp(E* + bp p* cos q*) with bp 1

  • Limiting cases:

cos q = +1 → Emax = 1.0 Ep

0.57 < Em / Ep < 1

cos q = -1 → Emin = 0.57 Ep

The M2 beam line for COMPASS


The m2 beam for compass

MUON POLARISATION

m

SPIN

Muons from pion decay are naturally

polarised through Parity Violation:

n

For the typical COMPASS

conditions, pm / pp = 0.92 and

the measured muon polarisation

is about -80%

Note:

Average pion decay lengthis 55 metres per GeV/c

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

The muon beam consists of several sections:

  • The production target T6

  • Pion acceptance and momentum definition section

  • A pion decay volume (600 metres long)

  • A hadron absorber

  • A muon transport and cleaning section

  • The final focus section

Choice of several target heads: the longer, the more flux

Large acceptance, Dp/p up to ±10%

Average pion decay length at 172 GeV/c is ≈ 9.5 km

To stop all hadrons and scatter muons as little as possible

Momentum selection (±3%) and cleaning by magn. colls

Steer and focus propoerly on COMPASS target

The M2 beam line for COMPASS


The m2 beam for compass

MUON BEAM – MOMENTUM

  • The muon momentum is based on physics requirements.

  • The ratio pm/pp is based on a compromise beween:

  • - Total muon flux

  • - Polarisation (higher for extreme pm/pp)

  • In muon mode there are 3 sections with different momenta:

  • 1) The hadron section of the beam, up to the end of the FODO

  • The momentum is usually pp = pm / 0.92.

  • Sometimes the M2 is coupled to P61: pM2 = - 1/2 pP61

  • 2) The section from the end of the FODO to the absorber

  • Here pint = pm + Nabs * 0.315 GeV to correct for dE/dx in the absorber

  • Normally Nabs = 7 (pm<140 GeV) or 9 (pm>140 GeV)

  • 3) The muon section of the beam, from the absorber till the end

  • Here the momentum is the required muon momentum.

Momentum

defining bend:

B1

B6

2006: pp/pm = 172 / 160 GeV/c

The M2 beam line for COMPASS


The m2 beam for compass

CONSIDERATIONS FOR M2 OPTICS

  • Transport pions as well as muons from their decay together

  • Pions are ‘matched’ into a long decay channel (> 5-10% of tp). The M2 decay channel is about 700 metres long!The pions themselves have a large momentum spread (10%).

  • Muons from their decay have a lower momentum and an even larger momentum spread.

  • They do not come from a single point.

  • The optics of the decay channel must transport both p and m.

The M2 beam line for COMPASS


The m2 beam for compass

  • Transport muon beam over a sufficient distance

  • After the hadron stopper (at the end of the decay channel) the muon momentum selection must be done by magnetic collimation.

  • The unwanted muons must be separated from the beam axis and ‘ranged out’ in the earth: the energy loss is about 0.5 GeV/m.

  • For 200 GeV muons this requires a length of  400 metres!The origin of the muons is not a point source but a long ‘tube’.

The M2 beam line for COMPASS


The m2 beam for compass

Both problems have a common answer:

FODO channels:

Regular array of alternately focusing and defocusing quadrupoles.

They have a very large momentum acceptance

The M2 beam line for COMPASS


The m2 beam for compass

o/cell f / L

301.93

361.617

451.305

601

720.85

900.707

1200.578

1440.525

1800.5

The M2 beam line for COMPASS


The m2 beam for compass

Muons

Choose 60o/cell

for the pions,

still very good

acceptance for

the decay muons

Pions

Acceptance

60

72

90

180

Phase advance per cell (degrees)

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

SPECIAL PROBLEMS FOR M2 OPTICS

  • Large momentum spread (up to ± 10%)

First order optics breaks down:

Rij(p) = Rij(po) + dRij/dp . po . (Dp/p) + d2Rij/dp2 . po2 . (Dp/p)2 + …

The (Dp/p)2 term is no longer negligible for larger Dp/p

Better use 2nd order optics for Dp/p >> 1%

  • Scattering in absorber introduces Dp/p  y, y’correlations

Faster particles (p > po) are bent less in B4+5

If they are scattered downward in the absorber, they are lost,

if they are scattered upward, they may be kept :

Need full

Monte Carlo

simulation:

HALO

This introduces a y’  p correlation (like dispersion).

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

In/out motorisation

HADRON ABSORBERS:

9 Be modules (1.1 m each) in 3 bends

The M2 beam line for COMPASS


The m2 beam for compass

B

Magnetic force

SCRAPERS(Magnetic Collimators)

Have to get polarity right….

The M2 beam line for COMPASS


The m2 beam for compass

4 Motors: 2 upstream, 2 downstreamallows to follow beam divergence

Have to stop current before moving jaws !!!

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

MIB: Magnetised Iron Block

B

Beam

Same function as scrapers

but bigger and no motors

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

Steering at the end of beam is very critical

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

Novelties for 2006:

  • One new scraper + MIB in front end of beam line (posn 200 m)Should solve a radiation dose problem at the ramp from bldg 892 to EHN1

  • Move one scraper from posn 685 to 845and add one scraper + MIB at position 1000Allows to reduce muon halo in COMPASS by about 25-30%

  • 500 Tons of passive Iron shieldhave been installed above thebeam lines in TCC2 to protect EHN1 from m’s from T6 & T4

The M2 beam line for COMPASS


The m2 beam for compass

OPERATIONAL ASPECTS

  • Initial tuning for 2006 done by EA physicist

  • Muon operation inherently stable (if equipment in correct state)

  • Have to keep proton flux on T6 stable and highNominal T6 flux 1.2 1013 pppPotentially an increase to 1.45 1013 ppp can be granted,depending on RP measurements early in the run

  • Important that at least 7 hadron absorbers are in the beamduring muon operation

  • COMPASS changes T6 target head themselves (low intensity runs)

  • Fine steering at the end is done by COMPASS, based on their own SciFi detectors

The M2 beam line for COMPASS


The m2 beam for compass

MONITORING OF M2 BEHAVIOUR:

  • General Status – look at beam intensity on ionisation chamber– look at halo rates (check with logbooks)– check static settings (T6, colls, TAX) in case of problems

  • Wire chamber profiles

  • Magnet status

The M2 beam line for COMPASS


The m2 beam for compass

Halo

rates

Muon flux

Scrapers

GENERAL STATUS (1):

The M2 beam line for COMPASS


The m2 beam for compass

Collimator settings

Static settings

GENERAL STATUS (2):

The Cesar version will be very similar

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

The full beam would plough into theCOMPASS detectors and trip or even

damage them in case of failure of SM1 or SM2

Similarly in case the dipole inside the COMPASS polarised target is switched on

SM1&SM2 interlock

Pol. Target

SM1

SM2

In those cases the SM1&SM2 interlock puts Bends 4&5 on “Delestage” to stop the beam line. No operator intervention is required.The situation re-establishes itself automatically as soon as the situation is healthy.Please note that COMPASS can disable this interlock from their control room

The M2 beam line for COMPASS


The m2 beam for compass

SM2

Max. field:1.8 T

Current: 5 kAmps

Power:3 MW

Weight:400 tons

SM1

The M2 beam line for COMPASS


The m2 beam for compass

Access Specialities for EHN2

Search boxes!

Crane access is forbidden with beam on. Special keys are needed.

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

M2

The M2 beam line for COMPASS


The m2 beam for compass

pM2 = -0.5 pP61 if P0 derived from T6 target

Coupling between M2 and P61 beam lines:

The M2 beam line for COMPASS


The m2 beam for compass

HADRON OPTICS

There are 2 versions for the M2 hadron optics:

  • An optics compatible with P61 operation

  • Runs out at 225 GeV/c

  • Q1-Q6 and B1 are now same as in P61 at –2 pM2

  • Momentum definition by COLL 1 and 3 only, giving rather poor resolution.

  • Allows M2 to operate e.g. in the last week of a long proton run

  • A high-energy optics

  • Runs up to 280 GeV/c

  • Q1-Q6 and B1 are now different from P61

  • Momentum definition by COLL 5, with better resolution.

  • This is the ‘reference’ optics, however still to be commissioned (in 2006?).

1) Short target head

2) Small TAX holes

3) Single beam momentum all along the beam

4) Hadron absorbers OUT

In 2006 only used under EA physicist control

The M2 beam line for COMPASS


The m2 beam for compass

The M2 beam line for COMPASS


The m2 beam for compass

ELECTRON BEAM MODE

This beam is produced as in the West Area, i.e.:

Secondary beam at  -100 GeV/c up to 5 mm Pb ‘target’,

Tertiary beam of –40 GeV/c from Pb target to experiment.

The Pb target is about 50 m upstream of B4+B5.

For this mode there is a special optics with focus at the Pb target.

Will only be used for one or a few days,

set up by EA physicist

The M2 beam line for COMPASS


The m2 beam for compass

INFORMATION ON THE WEB

  • On the SL-EA Web pages you may find (from the BEAMS page):

  • A User Guide

  • A Quick Reference

  • More detailed optics drawings of all modes

  • Detailed tuning procedure for the muon beam

  • Detailed tuning procedure for the hadron beam

  • Modications to the beam line for COMPASS

  • Summary of the commissioning progress

  • Description of access specialities

  • Examples of tuning sessions can be found in the M2 logbook

Cesar related information for M2 will be provided soon

The M2 beam line for COMPASS


The m2 beam for compass

Thanks for your attention!

Questions ???

The M2 beam line for COMPASS


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