To: Distribution 15 Oct 96

From: Martin Nordby, Stan Ecklund

Subject: Minutes of the IR Engineering and Physics Meeting of 11 Oct 96

Hard-Copy Distribution:

Bob Bell	41	David Kirkby	95
Lou Bertolini	LLNL L-287	Jim Krebs	41
Gordon Bowden	26	Harvey Lynch	41
Pat Burchat	95	Tom Mattison	17
David Coward	95	James Osborn	LBL B71J
Scott Debarger	17	Andy Ringwall	17
Hobey DeStaebler	17	John Seeman	17
Jonathan Dorfan	17	Knut Skarpaas VIII	18
Stan Ecklund	17	Mike Sullivan	17
Alex Grillo	95	Uli Wienands	17
John Hodgson	12	Mike Zisman	LBL B71J
Hank Hsieh	LBL B71J
David Humphries	LBL 46-161	Orrin Fackler	LLNL L-291
Roy Kerth	LBL 50-340	Lew Keller	41

Electronic Distribution:

Curt Belser	Rick Iverson	Jeff Richman	Jack Tanabe
Catherine Carr	Nadine Kurita	Natalie Roe	Rick Wilkins
David Coupal	Georges London	Ross Schlueter	Fran Younger
Fred Goozen	Joseph Rasonn	Joe Stieber

Small-Finger Bucking Coil Layout

Scott Debarger described the geometry of a bucking coil in front of Q2 and inside the support raft. Using the current Q2 cross section from 13 Sept. he located a coil next to the mirror plate. The mirror plate is 9.53 mm thick located 38 mm from the iron of Q2. The inner radius just clears the BSC + 3.5 mm for vacuum chamber. This puts the hole bigger than the inscribed circle of the quad bore. The outer size of the mirror plate follows the contour of the quad steel -28 mm and -10 mm around the LEB and HEB respectively.

The bucking coil is centered around the detector axis, encloses both beams, and has an inner radius tangent to the LEB hole in the mirror plate. A triangular cross section is chosen to fit inside the conical part of the support raft. It has an area of 10 cm^2 which could allow 50 turns of 0.188 inch conductor. There is 5 mm clearance, available for alignment of the Q2 assembly.

Scott presented the new envelope resulting from addition of mirror plate and bucking coil inside the support. It also has the correct Q2 length. Orrin says this will cut more steel out of the finger than his previous calculations.

One problem is getting cables out past the bucking coil. The space above and below the septum mask is 6385 mm^2 and the coil/mirror plate allow 3845 mm^2 as presently drawn. James Osborn suggested an elliptical bucking coil to make room. We would need to check if it could fit over the round vacuum flange. Stan suggested two smaller coils, one each on HEB and LEB, but there is no room at septum chamber and assembly on vacuum chamber is harder, if not impossible.

Orrin asked if the Raft was stiff enough or would more need to be cut out of fingers. The answer is that we don't know yet, but expect to need a gusset on the canoe part of the raft.

Orrin expects the bucking coil will need to be stronger and hence a bigger cross section, given change to the steel in the third finger. Scott expects that the cross section can be 50% larger; he will check and get back to Orrin.

The bucking coil on the back side was discussed. George London finds he needs two coils, one on Q2, one large radius, in order to buck both the Q2 field and the DIRC phototubes.

Orrin will be doing calculations with the new envelopes.

Q2 Magnet 3-D Analysis

James Osborn gave a status report on the 3-d Amperes calculation of Q2. The model has 1/4 symmetry, (1/2 symmetry in the transverse plane and 1/2 in longitudinal z direction) corresponding to the actual Q2. He finds harmonics n=3,4,5 about 2E-3 (relative to quad harmonic) and 6 E-3 for n=6 at a reference radius of 4.23 cm. These are larger than tolerance by factors of 10-60 and will need correction. Corrections anticipated are dipole winding to affect n=3, end chamfering for n=6, and harmonic correction ring. Next steps are to put in a mirror plate, bucking coil, and a solenoid coil to simulate the BaBar solenoid field leakage and calculate the induced skew octupole.

Hobey showed a re-analysis of Fran Younger's 3-d Amperes model of Q2 with solenoid fringe field. We extracted the harmonics as a function of z. The interesting point is that the induced skew octupole and radial field both peak in front of the magnet iron. This implies that a mirror plate with a round hole should be very effective at reducing induced octupole. This conclusion could be dependent on how the solenoid fringe field was generated.

H.O.M. Analysis of Near IR Chambers

Eddie Lin reported on higher order mode calculations for the Vertex Vacuum Chamber. His 3-d model included the new Q1 vacuum chamber and extends from -2 m to +2m. He assumed a 3 amp beam for power calculations. The structure has resonances between 3.5 and 4.2 GHz. The power mostly goes into the Be because it is the smallest diameter. If harmonics of the beam spacing do not match any of the structure resonances, the power is quite low, on the order of 9 watts.

However, if one or two resonances are hit, the power can be higher, more on the order of 100 watts, depending strongly on the Q of the resonance. Eddie will try to refine an estimate of Q for next week. One way to lower the power is to incorporate a lossy material in the vacuum chamber. SiC is being used by KEK.

HER Quad Magnetic Measurements

Stan reported on magnetic measurements John Seeman requested of a HER 560 quad with solenoid field. The new data has the solenoid plane rotated from the vertical by 35 degrees (55 degrees from horizontal line to plane of coil). This is to estimate the effect of transverse leakage field from the BaBar solenoid due to the lack of axi-symmetry. Data was taken with a round mirror plate with inside diameter of 4.75 inch. Field maps (Hall Probe) were taken and harmonics of induced fields measured with only the solenoid energized.

Harmonics are shown for six configurations, three with normal solenoid, three with rotated solenoid, and no mirror plate, quad shaped mirror plate, and round mirror plate. The normal data are consistent with previous results which sets the tolerance for Bz at Quad (effective) edge of 100 gauss. The rotated solenoid data gives harmonics about twice CDR tolerance specification with measured radial field components ranging from 4 to 52 gauss. Setting a spec on maximum Br is difficult because of this strong variation; but an estimate is Br<13 gauss at the mirror plate of Q2.

These minutes, and agenda for future meetings, are available on the Web at:

http://www.slac.stanford.edu/accel/pepii/near-ir/home.html