To: Distribution 12 Dec 96

From: Martin Nordby

Subject: IR Engineering and Physics Meeting Minutes of 6 December 96

Hard-Copy Distribution:

Bob Bell 41 Nadine Kurita 18
Gordon Bowden 26 Jim Krebs 41
Pat Burchat 95 Harvey Lynch 41
David Coward 95 Tom Mattison 17
Scott Debarger 17 James Osborn LBL B71J
Hobey DeStaebler 17 Andy Ringwall 17
Jonathan Dorfan 17 John Seeman 17
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 Lew Keller 41
Roy Kerth LBL 50-340
David Kirkby 95

Electronic Distribution:

Curt Belser Kay Fox Jeff Richman Joe Stieber
Lou Bertolini Fred Goozen Natalie Roe Jack Tanabe
Catherine Carr J. Langton Ross Schlueter Rick Wilkins
Al Constable Georges London Knut Skarpaas VIII Fran Younger
David Coupal Joseph Rasonn Ben Smith

Q2 Shielding Plug Summary

Stan Ecklund put together a "status-to-date" summary of the Forward Q2 Shielding Plug analysis to better understand where we are, and where we need to go. Below is a summary of that summary, while more details are provided in the enclosed slides.

Stan discussed seven different models run by Stefan Mikhailov while he was at SLAC. These were all 3-D runs of the Q2 Magnet, with a conical solenoid coil used to generate a nearly identical field distribution along the detector axis as that predicted by detailed 2-D axi-symmetric analysis of the real detector with an approximate Q2 Magnet geometry. The goal was to design a "small-finger solenoid" which fits around the Q2 Septum Chamber in front of the Q2 Magnet, to buck out the stray field from the BaBar solenoid. Different combinations of solenoid and shielding were tried.

The target value for harmonics in Q2 was defined in the CDR to be 40-60 G-cm for each harmonic. Notably, for B4, the CDR spec is 61 G-cm. Tracking studies have shown that at 3 X CDR harmonics, the LEB dynamic aperture is affected.

Model #1 run by Stefan omits any bucking solenoid, with a single mirror plate, as laid out by James Osborn for Q2, and a 1 cm chamfer on the end of the Q2 iron core. B4/B2 = 2.6 X CDR, which is considered not acceptable. Models #2 and #3 varied the Q2 core chamfer, with all other conditions being equal. A 3 cm chamfer reduced octupole in Q2 by 50%, but this could not be counted on, since chamfer size will be determined solely by field maps of the Q2 Magnet.

Model #4 includes a racetrack bucking solenoid running at 1900 Amps, a shield around the solenoid, the standard Q2 mirror plate, and a 3 cm chamfer on the Q2 core. B4/B2 is nearly 0, but n = 3, 5, and 7 increases to up to 20 X CDR, which is clearly too large.

Model #5 attempts to deal with the other harmonics by adding an additional mirror plate with two holes in it, so the bucking solenoid is trapped on both side by mirror plates. This includes a racetrack bucking solenoid running at 1550 Amps, a shield around the solenoid, the standard Q2 mirror plate, a 3 cm chamfer on the Q2 core, and an additional mirror plate in front of the solenoid. All harmonics are below the CDR tolerance, except B3/B2 = 1.33XCDR. This solution looks like it works well magnetically, but there is no physical room for the second mirror plate, since the Q2 Septum Chamber occupies all space in front of the magnet around the beams, and it cannot be shortened.

Model #6 includes a racetrack bucking solenoid, running at 5000 Amps, no shield, a standard Q2 mirror plate, a 3 cm chamfer on the Q2 core, and no additional mirror plate. All harmonics are OK, except B3/B2 = 2.78 X CDR, and there is a significant induced skew quad field, which should be correct-able, but could be a problem. This solution apparently trades the induced octupole for an induced sextupole plus a few kilowatts of heat.

Model #7 was a throw-back to simpler times, including just a round bucking solenoid, which fits outside the Q2/4/5 Raft cone and is actually capable of being installed. This included the round bucking solenoid running at 15,000 Amps, no shield, a standard Q2 mirror plate, a 1 cm chamfer on the Q2 core, and no additional mirror plate. B4/B2 = 0.95 X CDR, but all other harmonics are lit up like a christmas tree, since the racetrack-shaped double-holed Q2 mirror plate sees varying solenoid fields from the round solenoid.

All harmonics discussed above are actually skewed, since everything modelled is symmetric about the horizontal plane. Stefan is continuing to study this problem, focussing on a passive solution by shaping the single mirror plate to produce an opposite sign skew octupole. This may solve the stray field problem, but could affect harmonics of the magnet when the solenoid is off.

These models all assumed that the Q2 mirror plate is mounted to the core with about 100 cm^2 of iron, to allow field to shunt to the outside of the core. James Osborn felt that there was room for this, but his current coil turn-around and clamp design would need to be modified.

David Humphries will investigate adding an octupole correction ring outboard of Q2 which corrects for the induced octupole, instead of trying to eliminate it.

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