mice magnetic fields & shields
DESCRIPTION
J. H. Cobb & H. Witte Oxford University. MICE MAGNETIC FIELDS & SHIELDS. Magnet fields for MICE (VI) calculated including magnetic shield discs at request of software people Minor adjustments to end-coil currents to get uniform field in spectrometers - PowerPoint PPT PresentationTRANSCRIPT
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
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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
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• 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....
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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
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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?)
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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