PID PC 7th Sept 2005 1

MICE MAGNETIC FIELDS & SHIELDS

J. H. Cobb & H. Witte

Oxford University

Magnet fields for MICE (VI) calculated including magnetic shield discsat request of software people

Minor adjustments to end-coil currents to get uniform field in spectrometers

Recalculate fields at positions of PID detectors with shields

All documented in MICE Note 119, q.v. for details

Some comments on possibility of lighter shield

Some minor amendments/additions for PID meeting 7/9/05

PID PC 7th Sept 2005 2

Shield:100 mm soft iron400 mm from end coil

Spectrometersolenoid

PID PC 7th Sept 2005 3

Calculations made with FemLab after comparison with OPERA

B in solenoid – no visible differencebetween FemLab & OPERA

Used OPERA default B – Hcurve for soft iron

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Field in ironAverage ~ 1.5 T – not saturatedHot Spot is artefact of FEA calc.

OUTSIDE

INSIDE SOLENOID

Z

r

Bz in channel, r = 0Minimal difference iron/no ironexcept at ends

PID PC 7th Sept 2005 5

External B (obviously) less with ironBeam less confined Problem ?? TBD (software folk)

Shi

eld

Adjust end-coil current only by ~2.5% to give dB / B < 1% in solenoidi.e. like no iron

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Shielding efficiency – summary table follows

TOF

Ckov

EMCal

|B|

r

Black = No Iron

Red = with Iron

Residual B @ EMCAL ~2x higherthan shown in TDR ~ 38mT

PID PC 7th Sept 2005 7

• Fields with currents adjusted for the iron are calculated & available as z – r map

• Fields at positions of TOF, Ckov & EMCAL calculated S/W & PID people must see if they are OK• This Shield does little for EMCAL

• NOTE No allowance for ‘Tunnel’ (shielding around hall)

• Investigate if it’s possible to reduce amount of iron for same shielding efficiency by subdividing shield....

PID PC 7th Sept 2005 8

Subdivide Iron Shield -- Summary (plots follow)Fields in mTeslaDiscs 0 1 1 2 2 2 2 2 10 10 (TDR w.Tun- w/o Tun)------------------------------------------------------------------------------T1 0 100 165 50 50 50 50 25 5| 6.35| 100mmT2 0 50 25 25 10 25 -x10 -x10Gap 0 50 50 10 25 25 5| 6.35|------------------------------------------------------------------------------Tot Fe 0 100 165 100 75 75 60 50 50 63.5 100mm==============================================================================TOF 246 105 92 90 98 110 117 124 118 102 80 --100------------------------------------------------------------------------------Ch 96 68 66 66 67 67 69 48 -- 60Cal 46 36 39 .... all ~35 38 22 -- 28 Now/TDR~1.8-------------------------------------------------------------------------------TOF @ r = 25cm Chkov @ r = 38cm Cal @ r = 35cm

Total Fe(mm) 0 50 60 64 75 100 165 ----|-------------------------------|Total Gap 0| 246 105 92 | (mm) 10| 110 | 25| 124 117 [105] [97] | 50| 118 *109 98 90 | 57| 102 | |-------------------------------|

Including more from HW 23 Aug, i.e. since VC.

PID PC 7th Sept 2005 9With 165mm of Fe (23 Aug 2005)

|B| at TOF for 8 configurations of Iron Discs & Gap

PID PC 7th Sept 2005 10

A LOOK AT SCRAPING IN SHIELDRMS beam radius can be calculated assuming:

Gaussian Beam

Beta function and

Emittance

Choose 200 MeV/c SFOFO

‘beta = 42cm’ and emittance that scrapes (at some level) in absorbers (r=15cm)

scale by sqrt(beta) Shield

sigma(x) = sqrt {beta*(m/p)*epsilon-N} Reduction of Bz due to iron does not matter since ~ in drift region outside tracker solenoid (see page 5)

Gaussian beam,

Fields without iron

PID PC 7th Sept 2005 11

Summary

• Field maps exist; scraping probably not problem for 25cm hole

• Need response from PID group on residual fluxes– Is 105 mT OK? – Safety Margin?– Further reduction more iron and/or space

• Shield does a lot for TOF, some for Chkov, little for EMCAL

• Possible ‘Shield Lite’ solution using 10 x 1/4” plates (though is it worth the extra effort?)

PID PC 7th Sept 2005 12

Subdivide Iron Shield -- Summary (plots follow)Fields in mTeslaDiscs 0 1 2 2 2 2 2 10 10 (TDR w. Tun-- w/o Tun)------------------------------------------------------------------------------T1 0 100 50 50 50 50 25 5| 6.35| 100mmT2 0 50 25 25 10 25 -x10 -x10Gap 0 50 50 10 25 25 5| 6.35|------------------------------------------------------------------------------Tot Fe 0 100 100 75 75 60 50 50 63.5 100mm==============================================================================TOF 246 105 90 98 110 117 124 118 102 80 -- 100------------------------------------------------------------------------------Ch 96 68 66 66 67 67 69 48 -- 60Cal 46 36 39 .... all ~35 38 22 -- 28 Now/TDR~1.8**-------------------------------------------------------------------------------TOF @ r = 25cm Chkov @ r = 38cm Cal @ r = 35cm

• B @ TOF most sensitive to shieldconfiguration

• Shield does ~0 for EMCAL !!

• Subdivision gives equal shielding with less iron but more total length

Total Fe(mm) 0 50 60 64 75 100 ----|---------------------------|Total 0| 246 105 |Gap (mm) 10| 110 | 25| 124 117 [105] [97]| 50| 118 *109 98 90 | 57| 102 | |---------------------------|

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10 x 6.35mm (0.25”) plates + 9 x 6.35mm gaps |B| = 102 mTc.f. 105 mT for single 100mm plate

Total length = 121mm; saves ~35% of the mass of the iron for extra 21mm

|B| at TOF for 7 configurations of Iron Discs & Gap