To: Distribution 13 Sep 96
From: Martin Nordby
Subject: Minutes of the IR Engineering and Physics Meeting of 6 Sep 96
|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|
|Catherine Carr||Nadine Kurita||Natalie Roe||Rick Wilkins|
|David Coupal||Georges London||Ross Schlueter||Fran Younger|
|Fred Goozen||Joseph Rasonn||Joe Stieber|
|Rick Iverson||Jeff Richman||Jack Tanabe|
Fields in Q2
John Seeman reported on further refinement of comparisons between the Q2 / solenoid testing he had done, and the analysis done by Orrin Fackler. For these tests, the quoted solenoid field was measured one inch off the front of the core, near the center of the bore. This corresponds to the 2.4 m location in Orrin's calc's. At a radius of 4 cm, the calculations predict Bz = 250 G, and Bmod = 260 G. This difference has not been accounted-for, and may be offset by other discrepancies, so should not be counted on. However, future field quotes should be for Bz, at this one inch location.
John also reported that the octupole coils in Q2 produce a 16-pole
field which has the same polarity as that induced by the solenoid.
There was some hope that the polarities would be cancelling, but,
since they add, the limit of the octupole field is 375 G, to maintain
the 16-pole field below the spec for Q2.
Comments on Q2 3-D Analysis
Stan Ecklund reported on attempts to correlate Fran Younger's 3-D analysis of Q2 with the tests done by John Seeman, et al. The 3-D analysis showed that the radial field entering the pole tips from the solenoid field is sinusoidal with the poles. Assuming that all Bz becomes Br and enters the pole tips:
int(Br(z)*dz) = Bz*r0 / 2 (for r0 = 4.78 cm)
This yields 186 G-cm for r0 = 4.78 cm, and 129 G-cm for r0 = 4.23 cm
The latter reference radius was used by Fran in his 3-D calculations. He predicted 117 G-cm integrated octupole This agreement suggests that 90% of the Bz entering the bore produces integrated octupole.
The simple sinusoidal model also agress to 30% with the tests
done on the HER quad.
BaBar Magnetic Analysis
Orrin Fackler reported on ongoing work to optimize/understand the Q2 shielding plug finger design. To satisfy curiosity, he ran a model of the forward plug with solid fingers, using KEK Venus steel. Bmod = 6000 G in Q2, compared with 187 G for the same configuration with fingers.
He then thickened the fingers at their root, but this shunted more flux from the first to the second finger, and from the second to the third, which pushed more out into Q2. Bmod = 211 G in Q2 for this configuration.
To bound the problem, Orrin ran a case with mu = 20 kOe to eliminate any saturation effects. Here, Bmod = 32 G in Q2. This is lower than an earlier simulation where he reduced the solenoid field to 1.7 kG, ran the calc's, then multiplied results by 10X. This showed that, even at 10% of field, parts of the fingers were still being saturated.
Another set of runs investigated the sensitivity of field in Q2
to the shape of the top end of the B-H curve. This part of the
curve has been extrapolated, since reliable test data was not
available. Following is a list of stray fields for various curve
|Pure Fe (measured)|
|KEK(lower curve, extrapolated)|
|KHI extrapolated data|
This shows that sensitivity to poor definition of the B-H curve above 100 Oe is only at the 10% level.
Next, Orrin modified the plug geometry to fit the Q2/4/5 Raft design in its present incarnation. Specifically, he opened up the flare of the third finger to miss the flare of the Raft, and straightened the second and third finger to make the parts more build-able. Neither had any effect on stray field in Q2 (at the 5 G level).
Finally, Orrin looked at the effect of reducing the main solenoid
field on the stray field. For the two types of steel listed below,
stray fields changed significantly with main field magnitude:
Stray Field in Q2:
This suggests that reducing the solenoid field can never help
more than to bring Bmod down to 60 G. Orrin feels that a bucking
coil near Q2 should bring the field down to <100 G. This is
based on his past experience with adding bucking coils to this
--Look at a water-cooled copper bucking coil, running at 10 A/mm^2. Plan to support the coil off the Raft, and minimize its cross-section to reduce the quantity of steel which is removed (Orrin Fackler).
--Look into using annealled steel, either KHI or KEK Venus steel.
--Map Bz and Br over the entire length of Q2, to better understand
the analysis results, and correlate with tests.
These minutes, and agenda for future meetings, are available on the Web at: