To: Distribution 4 Feb 97

From: Martin Nordby

Subject: IR Engineering and Physics Meeting Minutes of 31 January 97

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

Shielding Plug Area Layout

Scott Debarger reported on the final layout of the Q2/4/5 Rafts and Forward and Backward Shielding Plugs. The Back Plug clears the coil leads for Q2 by 0.27", at the point of closest approach. At z = 5250 mm, the water connections for the Q4 magnet stick into the path of the Back Plug as it is extracted. This happens at 2:00 and 8:00 o'clock, with an interference at both places of 0.25". Since the fittings are stacked two or three deep, elbows cannot be used, and the packaging cannot be made tighter.

Furthermore, the layout used the actual Plug dimensions, not a stay-clear value, to account for alignment and fabrication errors in the Plug. When this 5 mm is added on, the bore of the backward Plug must be increased by 1 cm in radius to ensure there is no interference during withdrawal. Also, at the 8:00 o'clock position, an additional rabbet is needed to allow room for the coil leads. The iron removed from the move-able Plug can be added to the fixed portion, so there is no net loss of iron. Although this is only a 1 cm wide piece, there was strong opposition by BaBar to moving this material. We will meet off-line with Johanna Swan, the Q4 Magnet engineer to look into moving the coil leads, if possible (and schedule permits).

The Q5 LEB Chamber has been notched, and the ion pump on the Q4 LEB Chamber reduced from a 220 L/s pump to a 60 L/s Pump to allow room for the Plug extraction. The LEB corrector between Q4 and Q5 no longer interferes with extraction, since it fits into the notched chamber. All magnets will be shielded, so the power supplies will NOT NEED to be locked and tagged (however, they can be for access, if desired by BaBar personnel).

Plug Magnetic Analysis

Lew Keller reported on analysis of the "final" Plug configurations, which include changes proposed by Kawasaki Heavy Industries, and by PEP-II.

Back End

On the Back End, increasing the Plug radius by 1 cm decreases the peak radial field in the Q1 Magnet from 2.4 kG to 2.35 kG (using 2-D axisymmetric MERMAID model). The axial force on the solenoid cryostat is reduced by 700 lbs. However, the back end bucking coil will most likely have to be increased in strength, and Georges London needs to investigate the effects on stray fields in the DIRC PMT's. Lew will also be looking at field uniformity in the Drift Chamber active volume, but felt that this should not be significantly impacted.

Conclusion and Decision

--Open up the Back end Plug bore by 1 cm in radius to 37 cm.

Forward End

3-D modelling done by Stefan Mikhailov showed that, for differing depths of chamfer on Q2, the fraction of axial flux converted to octupole in Q2 changes. For a 1 cm chamfer, 30% of the axially field resulted in skew octupole. This is far less than the 100% previously assumed.

Lew used this scaling to correlate results from his 2-D axisymmetric model with the expected octupole due to the real, 3-D fields. He ran three models.

1. Baseline design.

2. KHI Mod 1: included proposed changes by KHI, which included closing the gap between fingers 2 and 3, making the bore out of stepped cylinders, rather than frustrums, and making the second and third finger tips be planar washers, rather than gently sloping dishes as called-for in the baseline design.

3. KHI Mod 2: included changes proposed, above, plus an increase to the radius of the Plug bore and third finger by 3 mm. This accommodated the expected increase in the wall thickness of the Q2/4/5 Raft (see below).

Results for the three runs are shown, below, for a 1 cm chamfer on Q2, with a mirror plate. Bz is the field measured at the mirror plate. The central field for these runs is 17 kG, unless otherwis noted.

Ratio to PEP-II CDR
81 G
0.060 kG-cm
KHI Mod 1
KHI Mod 2
KHI Mod 2 (B0=15 kG)

For KHI Mod 2, field values for all magnets are listed below. This includes a 17 kG main solenoid field, , one main bucking coil around the DIRC SOB, but no coils around Q2 at either end, and no "Q4 Bucking Coil" on the forward end door.

Ratio to PEP-II CDR
Forward End
Q2 Front
116 G
0.086 kG-cm
Q2 Rear
Q4 Front
Backward End
Q2 Front
23 G
0.017 kG-cm
Q2 Rear
Q4 Front

Conclusions and Decisions:

--Open up radius of Forward Plug bore and third finger inside profile by 3 mm

--Open up radius of Back Plug bore by 1 cm to 37 cm

--Eliminate Forward End Q4 Bucking Coil

--Eliminate Back End Q2 bucking coils

Q2/4/5 Raft Analysis

Scott Debarger and John Hodgson reported on analysis of the Forward Q2/4/5 Raft, and design modifications to increase its stiffness. The analysis showed that the box beam and Y transition region, as well as the forward transition and cylinder/cone parts, needed stiffening. Some stiffening was accomplished by thickening members, improving the cross-bracing, and filling in the Y. It was found necessary to increase the thickness of the cylinders and cone from 3/8" to 1/2" to reduce the peak stress at the cone/cylinder welded joint to a safe level during installation. To maintain safe stress levels in this region during a seismic event, the half-cylinders were closed-out with structurally integrated tops.

Below is a summary of the results. All models include "real" magnets, with actual struts modelled, to pick up modes which include individual magnet motions. The loaded Raft weighs 25,900 lbs (22,450 lbs of equipment plus 3450 lbs for the Raft itself), and is supported at 2 points under Q5 and 1 point under Q4 during operation. Unless otherwise indicated, deflections and stresses listed below are for this support condition and 1 g gravity loading. Natural frequencies listed below also assume operational support conditions. In an earthquake, the support under Q4 breaks away, and a "Seismic Bracket" mounted to the BaBar door picks up the very in-board end of the Raft. Earthquake (EQ) stress values shown below are for this support case.

"Baseline" design:

Includes a small gusset under the Q2 Magnet and Septum Chamber. Box beams under Q5 are 6 x 6 x 1/4" wall with a 4 x 6 x 1/4" wall channel welded under it, and partial cylinders under Q2 and septum are 3/8" thick.

Deflection at in-board end: 0.107"

f1: 6.0 Hz

Mode shape: Q5 pitches axially, distorts Raft locally, Raft kinks vertically between Q4 and Q5.

f2: 8.8 Hz

Mode shape: Q4 and Q5 pitch transversely on Raft, Q4 more so than Q5; Raft racks under Q5, twists between Q5 and Q4.

"Stiff Raft" design, 3/8"-thick nose:

Replaced box beams and channels under Q5 with 1"-top/bottom-plate, 10" x 1/2"-side-plate box beams. Added 3/4" plates to close out top, bottom of the Y-transition region between Q4 and Q5, and connect top to bottom with a shear plate. Removed gusset under septum, increased thickness of canoe-to-cylinder transition piece from 3/8" to 1/2".

Deflection at in-board end: 0.113"

f1: 9.0 Hz

Mode shape: full-body deflection, with in-board end kinking at cone/cylinder joints

f2: 9.9 Hz

Mode shape: similar to mode 1 but in-board end kinking more pronounced

Max Von Mises stress in nose with distributed support tube load: 23.7 ksi (at welded cone/cylinder joint)

"Stiff Raft" design, 1/2"-thick nose

Increased thickness of both partial cylinders under Q2 and septum, and cone connecting cylinders, to 1/2". NOTE: Through bore of Plug, cylinder is now 1/2" thick.

Deflection at in-board end: 0.086"

f1: 9.2 Hz

Mode shape: full-body deflection, with in-board end motion subdued

f2: 11.1 Hz

Mode shape: in-board end bobbing vertically

Max Von Mises stress in nose with distributed support tube load: 13.6 ksi (at welded cone/cylinder joint)

"Covered Cylinder" design

Added a cover to complete the cylinders and cone around Q2 and septum.

Deflection at in-board end: 0.066"

f1: 9.3 Hz

Mode shape: full-body deflection, with in-board end nearly stationary

f2: 12.3 Hz

Mode shape: vertical bobbing of in-board end

Max Von Mises stress in nose, with distributed support tube load, under vertical EQ load (2 g vertical acceleration + 1 g gravity): 20.9 ksi

Max Von Mises stress in nose, with distributed support tube load, under lateral EQ load (2 g lateral acceleration + 1 g gravity): 20.6 ksi

Analysis Summary

Stiff, 3/8"
Stiff, 1/2"
Cover. Cyl.
0.107 in.
0.113 in.
0.086 in.
0.066 in.
6.0 Hz
9.0 Hz
9.2 Hz
9.3 Hz
f1 shape
Q5 pitch
full deflec
full deflec
full deflec
8.8 Hz
9.9 Hz
11.1 Hz
12.3 Hz
f2 shape
vert Q2 kink
vert Q2 kink
vert Q2 kink
Max oper. stress
23.7 ksi
13.6 ksi
Max EQ stress
20.9 ksi


--Use 1/2" plate on all cones and cylinders on in-board end, to reduce

stresses at joints

--Do NOT use any gusset under Q2.

--Plan on using a cover over Q2 to increase stiffness and reduce stresses

and deflections under earthquake loading.

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