To: Distribution 19 Feb 97

From: Martin Nordby

Subject: IR Engineering and Physics Meeting Minutes: 14 February 97

Hard-Copy Distribution:

Bob Bell 41 Nadine Kurita 18
Gordon Bowden 26 Jim Krebs 41
Pat Burchat 95 Harvey Lynch 41
Scott Debarger 17 Tom Mattison 17
Hobey DeStaebler 17 James Osborn LBL B71J
Jonathan Dorfan 17 Andy Ringwall 17
Stan Ecklund 17 John Seeman 17
John Hodgson 12 Mike Sullivan 17
Hank Hsieh LBL B71J Uli Wienands 17
David Humphries LBL 46-161 Mike Zisman LBL B71J
Lew Keller 41
Roy Kerth LBL 50-340
David Kirkby 95

Electronic Distribution:

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

Progress on Final IR S.R. Studies

Mike Sullivan reported on prgress in finalizing the S.R. fan masking and background studies in the Near IR. He has focussed his efforts on the -2m < z < 2 m region (Vertex, B1 and Q1 Chambers), and included all S.R. fans out to BV1 on the LER and B2 on the HER. The mask tips in the B1 Chambers are the primary background source for the SVT, especially the first tip on either side of the Vertex Vacuum Chamber. The chamber and mask geometry has been updated to incorporate suggestions from Eddie Lin to minimize HOM heating, and from Nadine Kurita and Martin Nordby to simplify fabrication.

For the Vertex Vacuum Chamber, the geometry has been modified to include the latest thinking on fabrication and plating from Knut Skarpaas and Nadine. The models use (from the inside out): 10 microns Au, 1.3 mm Be (2 walls), 1.5 mm H2O, 20 microns Al, 220 microns C (last two are on inner RF shield of SVT). This adds up to 1.22 radiation lengths at 90°, compared with the CDR value of 0.79 r.l.

Results show that backgrounds are completely dominated by scattering off the HEB mask tip. With all copper tips, the HEB tip produces 100 times the radiation dose of the first LEB mask tip. Dose rates are tabulated below:

Dose Rate
HEB Cu tip
20 krads/yr
HEB Au tip
6 krads/yr
HEB Ag tip
10 krads/yr
LEB Cu tip
0.23 krads/yr

The dose is highest on the side opposite the mask tip, and varies roughly as sin(theta/2). The above values are for dose on the first layer of silicon. Comparable doses are seen on the electronics for layers 1 and 2, although 0.010" of tantalum shielding would completely shield this.

The gold tip appears to work well in conjunction with the gold plating on the beryllium Vertex Vacuum Chamber, since the gold plating absorbs much of the particles emitted off the gold mask tip which would otherwise be absorbed in the silicon. Particles at other energies are not absorbed by the gold, but are also not absorbed by the silicon. Most of these end up buried in the outer shell of the B1 Magnet.

Mike's model has three features which he plans to modify in future upgrades. First, he models the silicon as infinite-length planes, so the program over-estimates the dose on the silicon by about a factor of 2. Second, the program does not include L-shell electrons (E = 11 keV). Finally, it assumes infinitely-sharp mask tips. The next step is to start simulating "rounded" tips to reflect reality and see how sensitive backgrounds are to tip radius.

Q2 Magnet Update

James Osborn showed results of magnetic analyses of the Q2 Magnet cross-section. Previously, he has looked at the effect of adding either pole bumps or displacing conductor windings, but not both in tandem. Current work shows that these two parameters do, indeed, interact. For a reference radius of 4.23 cm, the following results and observation were discussed.

B6: For the n = 6 harmonic, both increasing the length of the pole bump or increasing the conductor displacement of the inner conductor on the split-plane can eliminate the harmonic. Too much bump or displacement can easily produce an opposite-polarity harmonic, as well. For instance, a 1 mm conductor displacement coupled with a 2 mm long pole bump brings B6 close to zero.

B10: For n = 10, the same trends hold, but a given bump or displacement generally produces only half the effect for B10 as for B6 in reducing the harmonic magnitude.

B14: This shows the same trend, with increasing coil displacement reducing the harmonic, but at 20% the level of B10. However, increasing the bump length actually increases the B14 harmonic.

For each harmonic, there is locus of points which theoretically produces zero field for that harmonic. This locus is described by a curve and (surprisingly?) the curves for B6, B10, B14, and B18 appear to nearly intersect around a conductor displacement of 1.5 mm, and a pole bump length of 1.5 - 2 mm. James is looking into this further to finalize the cross-section of the coil package and magnet core. While it is too early to give up valuable space in the septum region, if the conductor only needs to be displaced by 1 - 2 mm towards the LEB, there will be more room left for the beampipe and for clearance.

James also looked at the octupole trims design, and found that 3 turns of #10 wire (2.6 mm thick) running at 10 Amps will easily meet Stan's requirement for trim. When located 22.5° off the horizontal and vertical planes of the magnet, the trims produce a harmonic B12/B4 = 11%. This is slightly higher than the previous packaging, but still looks reasonable.

Although this package is flatter than the initial concept, the Chamber design may drive this to be even lower profile against the pole face. James felt that going to #12 or #14 guage wire should not be a problem. Also, the turn-arounds at the ends could either be saddle-type or could be flat on the face of the pole, whichever is preferred to avoid conflicts with the chamber water tubing turn-arounds.

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