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MICE MAGNETIC FIELDS & SHIELDS

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

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MICE MAGNETIC FIELDS & SHIELDS

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  1. 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 • 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

  2. Shield: 100 mm soft iron 400 mm from end coil Spectrometer solenoid

  3. 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. OUTSIDE Z r INSIDE SOLENOID Field in iron Average ~ 1.5 T – not saturated Hot Spot is artefact of FEA calc. Bz in channel, r = 0 Minimal difference iron/no iron except at ends

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

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

  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 littlefor EMCAL • NOTENo allowance for ‘Tunnel’ (shielding around hall) • Investigate if it’s possible to reduceamount of iron for same shielding efficiency by subdividing shield....

  8. Subdivide Iron Shield -- Summary (plots follow) Fields in mTesla Discs 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| 100mm T2 0 50 25 25 10 25 -x10 -x10 Gap 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 -- 60 Cal 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.

  9. |B| at TOF for 8 configurations of Iron Discs & Gap With 165mm of Fe (23 Aug 2005)

  10. 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 Gaussian beam, Fields without iron 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)

  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?)

  12. 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 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 | |---------------------------| • B @ TOF most sensitive to shield • configuration • Shield does ~0 for EMCAL !! • Subdivision gives equal shielding with less iron but more total length

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

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