To: Distribution 24 Sep 96
From: Martin Nordby
Subject: Minutes of the IR Engineering and Physics Meeting of 20 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|
|Roy Kerth||LBL 50-340|
|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|
Q2 Shielding Plug Design
Jim Krebs reported about fabrication ideas for the Q2 Shielding Plug. Orrin Fackler's models have used average radii, aligned with the detector centerline, to simulate the PEP-II stay-clears. However, these stay-clears are offset by up to 44.5 mm with respect to the detector centerline, making a real Plug cutout asymmetric. This asymmetry results in a third finger which is cut much thinner than Orrin's model assumed, causing more, and asymmetric leakage fields.
Regarding fabrication, Jim showed one possible method, which involved turning two right circular cones in the Plug. The first, and larger cone, would be offset by the 44.5 mm, producing the notch in the third finger. The second conical cut is closer to the centerline of the Plug, cutting the bore for the Q2 septum chamber. However, Jim was concerned that this fabrication method would produce scalloping where the cuts met. Also, there was discussion how the off-center cones would terminate in the centered conical edges of the fingers. This would likely produce angled ellipses which would introduce further 3-D effects in the stray field.
The only way to magnetically model this is to assume the most
conservative cutout. This means turning the largest possible on-center
hole in the Plug. Orrin will look at this to try to bound the
problem. This still does not help solve the 3-D nature of a real
James Osborn reported on some fabrication concepts he developed in July. The first involves simply offsetting the cutouts and fingers in the Plug. This preserves the minimum finger thickness, and makes fabrication fairly straightforward. The bore through the cones still is put on the center of the Plug.
One possible disadvantage is that it may produce a left/right asymmetry in the returning flux in the IFR doors and barrel. Harvey did not think that this would be a problem, although it may produce transverse loads on the solenoid. Harvey and Orrin will look into this.
An alternative fabrication method is to leave the fingers on-center, but truncate them before they intercept the conical cutouts and leave a flat, annular surface to intercept the cutouts. This ensures that all cuts remain in the same z-plane, eliminating the tapered ellipses and some 3-D stray field problems. Since the cutouts still must be off-center, they still produce a thinner third finger on one side than the other.
Regarding the 3-D stray fields, a discussion ensued about how best to model just the Plug, to avoid the huge 3-D model of the entire detector. James said that LBL's experience with the 3-D Amperes code is that it does not accurately compute the correct result. They use it more to look at differences in load conditions, and not to search for a stand-alone result. This suggests that striving for a single end-all model may not be the best direction. BaBar people will look at this more.
Another discussion arose regarding the need for offset cutouts
in the Shielding Plug. Lew Keller brought up the possibility of
rotating the detector towards the LEB to minimize or eliminate
the asymmetry. However, this has potentially large impacts on
the solenoid compensation scheme and orbits for both beams. The
HEB, especially, would be steered more by the solenoid, so it
would need stronger correctors and compensating quads and skew
quads. Also, since the solenoid was rotated to better handle the
vertical compensation, reducing the 20 mrad yaw angle could introduce
problems with the vertical dynamic aperture. This idea was dropped.
--Run the worst-case (largest, on-center) cutout in the Plug (Orrin Fackler)
--Develop realistic fabrication methods, including trying to maintain
the thickness of the third finger (Jim Krebs)
Q2/4/5 Raft Update
Scott Debarger reported on progress in stiffening the Raft. The shape transitions are the weakest part of the Raft, so this is where the focus has been. First, the transition from canoe-shaped Raft under Q4 to U-shaped cone under Q2 has been smoothed out by tapering the vertical walls further along the Raft, and adding a top plate which ties into the top of the canoe box section. This effectively extends the box section up under Q2
To stiffen the other end of this transition, which sits under Q2, the U-trough under Q2 has been extended further outboard to meet the new top plate. This region was originally not used for supports, but is the only place to grow into. James Osborn was concerned that this ate into the volume he would need for Q2 Magnet peripheral equipment like water manifolds, power connections, supports, and clamps. Although this new support does not extend beyond the outboard end of the magnet, its impact on the magnet needs to be investigated.
The final transition region occurs at the inboard end of Q2, where the Raft U-section is reduced down to very small diameter to sneak through the hole in the Shielding Plug. This transition cone is very flat, so it can easily oil-can. Scott plans to thicken it up on the inside, but space is limited. Ideally, he wants to add a gusset at 6:00 o'clock which reaches into the split-plane of the door Plug. This would require a 1 cm relief in the third finger to make room for the gusset.
Scott will model this to see how much it helps, and Jim and Harvey
will look at how this fits into the fabrication of the Plug.
--Finish new model of Q2/4/5 Raft and run deflection, stress, and modal analyses (Scott Debarger).
--Look into effects of a gusset through the third finger of the
Plug (Jim Krebs)
New Magnet and BSC Numbers
The video link got cut short by a power outage in the Computer Building at SLAC. However, Mike Sullivan has recently finished compiling new BSC and magnet position numbers for the entire IR straight. John Seeman has compiled a spreadsheet of space in the septum region from Q2 out to Q5 which uses these new numbers. The spreadsheet is included in the hardcopy, and the BSC and magnet position files are available at:
PEP-II Server:: pepii-server/Public/ir/data
These minutes, and agenda for future meetings, are available on the Web at: