PID PC 7th Sept MICE MAGNETIC FIELDS & SHIELDS J. H. Cobb & H. Witte Oxford University 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 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 Shield: 100 mm soft iron 400 mm from end coil Spectrometer solenoid

PID PC 7th Sept Calculations made with FemLab after comparison with OPERA B in solenoid – no visible difference between FemLab & OPERA Used OPERA default B – H curve for soft iron

PID PC 7th Sept Field in iron Average ~ 1.5 T – not saturated Hot Spot is artefact of FEA calc. OUTSIDE INSIDE SOLENOID Z r B z in channel, r = 0 Minimal difference iron/no iron except at ends

PID PC 7th Sept External B (obviously) less with iron  Beam less confined  Problem ?? TBD (software folk) Shield Adjust end-coil current only by ~2.5% to give dB / B < 1% in solenoid i.e. like no iron

PID PC 7th Sept Shielding efficiency – summary table follows TOF Ckov EMCal |B| r Black = No Iron Red = with Iron Residual EMCAL ~2x higher than shown in TDR ~ 38mT

PID PC 7th Sept 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 Subdivide Iron Shield -- Summary (plots follow) Fields in mTesla Discs (TDR w.Tun- w/o Tun) T | 6.35| 100mm T x10 -x10 Gap | 6.35| Tot Fe mm ============================================================================== TOF Ch Cal all ~ Now/TDR~ r = 25cm r = 38cm r = 35cm Total Fe(mm) | | Total Gap 0| | (mm) 10| 110 | 25| [105] [97] | 50| 118 * | 57| 102 | | | Including more from HW 23 Aug, i.e. since VC.

PID PC 7th Sept With 165mm of Fe (23 Aug 2005) |B| at TOF for 8 configurations of Iron Discs & Gap

PID PC 7th Sept A LOOK AT SCRAPING IN SHIELD RMS 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 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 Subdivide Iron Shield -- Summary (plots follow) Fields in mTesla Discs (TDR w. Tun-- w/o Tun) T | 6.35| 100mm T x10 -x10 Gap | 6.35| Tot Fe mm ============================================================================== TOF Ch Cal all ~ Now/TDR~1.8** r = 25cm r = 38cm r = 35cm TOF most sensitive to shield configuration Shield does ~0 for EMCAL !! Subdivision gives equal shielding with less iron but more total length Total Fe(mm) | | Total 0| | Gap (mm) 10| 110 | 25| [105] [97]| 50| 118 * | 57| 102 | | |

PID PC 7th Sept  10 x 6.35mm (0.25”) plates + 9 x 6.35mm gaps  |B| = 102 mT c.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