14 Aug 2008PC New task at last meeting (29 July): MICE magnets will be bolted to steel plates on floor of MICE Hall What – if any – is the effect of magnetisation of the steel on: field in channel & performance (cooling and Xmission) of MICE? Field maps may be available – forces have been calculated – from RAL I will look initially May have to include error fields in G4MICE / ICOOL Fairly urgent to understand this Module Plate Beams

14 Aug 2008PC Since last meeting Talked to Jim Rochford at RAL-ED 3D OPERA model of Coils + Shield Walls + Supports Very large & slow model – O(weeks) for field maps In fact, module support plates will be made of aluminium supported by steel I -beams  much less local steel  initial worry recedes Looked (with JR) at Opera 3D field calculations Observed some asymmetry in “Br” as function of azimuth (  ) at fixed r,z Offset of mag. axis means “Br” = sqrt(bx^2 + by^2) =/= true Br  asymmetry (  ) A = (Br(max) – Br(min))/Br(ave) = 2Xo/r  Xo = rA/2 x y  origin Magnetic axis at (say) (Xo, 0) Bx By r

14 Aug 2008PC Shield walls – extend the length of channel – will ‘pull’ field x y Coil Centred coil + 2 walls  X – Y asymmetry Off-centre coil + 2 walls  X (= L-R) asymmetry also Hard to estimate Need 3D field calculation with iron (mirrors) ~ – 4.6m + 3.7m

14 Aug 2008PC Looked here z = 5800mm (only place we looked) 3D Opera Observed A ~ 8% r=10mm A ~ 4% r= 20mm  Xo ~ 0.4mm (need to check not ‘mesh effect’) 0.4mm doesn’t seem bad BUT 1) looked in region (5800mm) screened by current sheet 2) region between FC & CC not screened 3) CC is largest coil – r = 0.8m  expect much larger effects ??? I am in contact with Jim R. He will re-run 3D calc. (had some incorrect J’s) & we shall look again at other z’s I expect big effects! TBC