1. MICE VC 17 Aug 20051 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

2. MICE VC 17 Aug 20052 Shield: 100 mm soft iron 400 mm from end coil Spectrometer solenoid

3. MICE VC 17 Aug 20053 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

4. MICE VC 17 Aug 20054 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

5. MICE VC 17 Aug 20055 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

6. MICE VC 17 Aug 20056 Shielding efficiency – summary table follows TOF Ckov EMCal |B| r Black = No Iron Red = with Iron Residual B @ EMCAL ~2x higher than shown in TDR ~ 38mT

7. MICE VC 17 Aug 20057 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 ~ nothing 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....

8. MICE VC 17 Aug 20058 Subdivide Iron Shield -- Summary (plots follow) Fields in mTesla Discs 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| 100mm T2 0 50 25 25 10 25 -x10 -x10 Gap 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 -- 60 Cal 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 shield configuration 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 | |---------------------------|

9. MICE VC 17 Aug 20059  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

10. MICE VC 17 Aug 200510 Summary Field maps exist Waiting for response from S/W & PID people on beam scraping & residual fluxes Note -- we find ~ twice residual field at EMCAL than value quoted in TRD 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?)