18 December, 2007 Analysis PC 18 Dec 20071

PIDer’s Question of Friday 14 Dec:

Dear John and Marco,

would you be able to give us a first preliminary ball-park answer to the following question?

Do you think MICE needs to map the (Kgauss or so) fringe fields upstream of the TOFI shielding cage?

Is the knowledge of these field maps relevant to the measurement of cooling?

The real question being : do we need to have the cage at Fermilab for magnetic measurements before we deliver it to RAL?

Any wisdom will help.

Already for the PID meeting today at 3.30 pm....

Best Vittorio

18 December, 2007 Analysis PC 18 Dec 20072

EFFECT OF SHIELD ON OPTICSShown at CM15 (Fermilab, June 06)

Shield

Bz small beyond position of shield even without shield

Muons drift

Expect effect of shield on downstream optics to be very small, if not entirely negligible

18 December, 2007 Analysis PC 18 Dec 20073

Since December 18....

• H. Witte passed D.Phil viva• Computed fields with 0, 1 & 2 shield plates

– End coil #1 current adjusted for one plate– not readjusted for two plates

• ‘Good field region’ good (< +/- 1%) in all cases– Presence of 2nd plate unimportant in this region

• Very little difference in Bz beyond 1st shield with 1 or 2 shields

– Maximum is at z = -6.8m ~12% of 0.1T = 120 Gauss (next page)

Shields

start at

z = -6.4m

Good field region

18 December, 2007 Analysis PC 18 Dec 20074

Ratio of axial fields in shield region with 0, 1, 2 shields

• 1st shield = 100mm thick Virostek disc

– -6.5 < z < -6.4m

• 2nd shield = 50mm thick disc

– -6.65 < z < -6.6m

• Outside shields effect of 1 or two shields is small

• No obvious need to measure with 2nd disc (or cage)

• Should be quite insensitive to precise material

Should answer PIDers’ question

Ratio of axial fields on axis