To: Distribution 18 Nov 96

From: Martin Nordby

Subject: IR Engineering and Physics Meeting Minutes of 15 Nov 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
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 Magnetic Analysis

Stefan Mikhailov reported on progress on magnetic analysis of the Q2 Magnet and solenoid stray fields on the Forward end. 2-D analysis of the BaBar stray fields shows that adding a racetrack shaped shield in front of the Q2 mirror plate significantly reduces the average Bz from 125 G to 25 G, sampled 1.2 cm off the front of the Q2 core. This shield extends off the mirror plate by about 5 cm, and is 1 cm thick. It surrounds a racetrack bucking solenoid coil, with a total cross-section of 7 cm^2, running at 850 Amp-turns. To effectively run this coil, the shield must be thickened up where it meets the mirror plate, to avoid saturation. This solenoid and shield only impact fields near the front end of Q2. At the back of Q2, and in Q4, its presence is not felt.

At the front of Q2, the following field values were found, using the racetrack solenoid, and integrating the field over the bore diameter, 1/4 radius off the front of the Q2 core:
Configuration Int. Field Bz
No shield 0.82 G-m^2 114 G
Shield w/out coil 0.18 G-m^2 25 G
Shield w/ coil 0.03 G-m^2 4 G
PEP-II Criteria 0.19 G-m^2 26 G

For Bz = 160 G, the integrated octupole field in Q2 is 116 G-cm (from a 3-D model of Q2 with solenoid). This assumes no chamfer in the core iron, and amounts to 5 X 10^-4 of the main quad field. This 3-D model includes the shield and bucking coil in front of the Q2 mirror plate.

For a 1 cm X 45 degree chamber, the integrated octupole drops to 40 G, and for a 3 cm chamfer, it is 30 G. This shows that the chamfer affects the model. Clearly, the final chamfer size will be set to reduce the built-in harmonics of the magnet, but this analysis could provide a scaling for expected induced octupole.

A comparison of Bz(z) field for the 2-D axisymmetric analysis with flux return fingers, and a 3-D model with a faked-in solenoid shows agreement to 5 G. This shows that the 2-D results with the new shield and racetrack coil design should be corroborated by the upcoming 3-D analysis. It also shows that the two analyses do agree, so 2-D models of the detector can be used to predict Bz in Q2 with reasonable accuracy. Stefan will continue to develop a 3-D model of the Q2 with racetrack shield and coil.

This bucking coil configuration requires two significant changes to the mechanical design of the region. First, the mirror plate must be tied to the core of Q2 with 100 cm^2 of material. James Osborn estimated that the current design has only 32 cm^2. He will look into modifying the coil clamps to make more room for increased tie size.

Second, the transition cone of the Q2/4/5 Raft will be enlarged, so the coil can go inside it. This should increase its stiffness, but will leave less room for cables and services to pass by. Also, if the racetrack coil needs to be water-cooled, it will not be able to be installed over the 10 inch vacuum flange on the end of the septum chamber.

The coil may be able to either be wound in place, or be made in two halves and plugged together electrically. Any cooling would come from a clamp-on cooling plate, or some other heat sink. As the coil requirements firm up, these options will be investigated.

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