1. 26 Aug 2008PC 325 1 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

2. 26 Aug 2008PC 325 2 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

3. 26 Aug 2008PC 325 3 3D Model of MICE + Hall shields and beams etc. (From Jim Rochford) Everything shown is either coil or ferromagnetic Compare field components Bx,By, Bz on axis with and without the iron Difference = Error field on axis

4. 26 Aug 2008PC 325 4 Bz on axis Flip Mode, 240 MeV/c Bx, By on axis (Gauss) 1G = 10 -4 Tesla should = 0 Max Br ~ 34 G = 3 x 10 -3 T Undoubtedly major effect from Coupling Coils at +/- 1.375m It takes ~ 24 hours to compute one set of 2700 points.....

5. 26 Aug 2008PC 325 5 Does this matter? A stupid calculation using error field alone gives ~20mm displacement for 200 MeV/c muon starting on axis  Big problem (but dumb calculation) Various reasons to think it does / does not. Various reasons to think it does not.  Need to track with a field map ! Problem – how to get field map in a finite time?? Possible Solution ‘Image Coils’ – but shield wall geometry is complicated To be continued