To: Distribution 2 Apr 97

From: Martin Nordby

Subject: IR Engineering and Physics Meeting Minutes: 28 March 97

Hard-Copy Distribution:

Bob Bell 41 Nadine Kurita 18
Gordon Bowden 26 Harvey Lynch 41
Pat Burchat 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
John Hodgson 12 Uli Wienands 17
David Humphries LBL 46-161 Mike Zisman LBL B71J
Roy Kerth LBL 50-340
David Kirkby 95
Jim Krebs 41

Electronic Distribution:

Curt Belser Tom Elioff Lew Keller Natalie Roe Dieter Walz
Lou Bertolini Kay Fox J. Langton Ross Schlueter Rick Wilkins
Adam Boyarski David Fryberger Georges London Ben Smith Fran Younger
Catherine Carr Fred Goozen Rainer Pitthan Steve St Lorant Ron Yourd
Al Constable Alex Grillo Joseph Rasonn Joe Stieber
David Coupal Keith Jobe Jeff Richman Jack Tanabe

Q2 Magnet Update

Using results from a number of 2-D magnetic analysis runs, James Osborn produced a graph of harmonic magnitude, as a function of conductor displacement and pole bump length. This shows the locus of points where b6, b10, b14, and b18 harmonics are zero. The graph shows that the b6 term is the most sensitive to changes in either the pole bump or conductor displacement. This is less so for b10, and still less for b14.

For a conductor displacement of 2.5-3 mm, and a pole bump length of 1.5-2 mm, all four harmonics are near zero. The analyses were run using 1006 Amps per turn, with an eight-turn coil, using a 1010 steel core, to model 3 GeV running conditions for the LEB. James found that changing to 1006 steel, or even infinite-mu steel, produces 1x10^-5 type effects on b6, and less on the other harmonics. Changes in coil excitation also have little effect.

These results are very good news. With a bump of 1.84 mm, and a conductor displacement of 2.64 mm, the b6, b10, and b14 terms should be reduced to near zero for the 2-D cross-section. The b6 term can then be corrected in 3-D by chamfering the ends, which will be needed, anyway, to correct for end-effects.

Regarding past discrepancies between POISSON and MERMAID codes, the differing results have been traced to two sources. First, POISSON has a problem with conformally mapping individual conductors into dipole space. The initial models included this (incorrect) mapping. Further modelling by James and Fran Younger identified this problem, and the conductors are now mapped as an assembly (James, Fran, and Klaus Halbach are following up on this, since this is a real limitation of the POISSON code).

In addition to this mapping error in POISSON, the 2-D models run on MERMAID also included a slight inaccuracy in the placement of the coils. Accounting for both errors, the two programs now produce near identical results.

Q1 Chamber Update

J. Langton presented the current design of the Q2 Chamber. The entire chamber will be made from copper sheet, bent up into U-shaped pieces for the HEB and LEB chambers. A separate sheet is bent, punched full of holes, and inserted into the HEB passage to serve as a screen to separate the NEG pump passage from the HEB beam passage. Both HEB and LEB chamber pieces come together around a copper block which houses the septum masks. The three pieces are electron-beam welded together.

The HEB chamber as shown interferes slightly with the Q2 mirror plate HEB cut-out. James Osborn felt that the cut-out could be centered more on the chamber, and J. felt that the chamber cross-section could be reduced somewhat at the corners to clear the hole.

At the in-board end of the Q2 steel core, the cooling tubes on the LEB chamber come very close to the main quad winding for the magnet. This could produce interferences at the end of the core, where the coil turns around. Also, it would force the coil package to be stepped. Neither of these options sounded nice, so the working decision was to back the cooling away from the quad coils, and make the coil package rectangular, filling the voids in the stepped conductor placement profile with G-10 shims. To make more room for the LEB chamber cooling, the octupole trims on the pole faces will be made from 12 gauge wire, possibly square.

Q2 Region of Raft

Scott Debarger showed progress on design of the Q2/4/5 Raft in the region of Q2. The Raft has covers which bolt to the bottom, U-shaped part of the Raft. The bolted joint transmits shear during earthquake loading, when the support point on the in-board end of the Raft carries 8400 pounds of the Raft load.

When the cover is removed and re-installed it will distort the Raft, so all components will need to be re-aligned. Furthermore, since the Q2 Magnet is bigger than the Support Tube, it will be difficult to see the end of the S.T. to align it, after the cover is installed.

The very in-board end of the Raft is made from a rolled up sector of a cylinder under the septum can. Currently, there is a small interference with both sides of the septum can and the bolted joint which joins the cover to this roll-up. Scott and J. will work on resolving this by thinning down the joint, and/or narrowing the chamber.

Both the Q2 Chamber and Magnet can be removed by lifting straight out of the Raft (when the cover is removed). No sliding or rotation is needed to finagle the components out.

On the out-board end of the Q2 Magnet, one of the four coil fan-outs interferes with the Raft. James plans to shorten this fan-out to keep it 3.75 inches from the angled edge of the magnet core. This will easily clear the Raft. However, the Raft layout hugs the Q2 magnet tightly (especially on the LEB side). Unfortunately, the magnet layout used to model the Raft did not include any tie plates to hold the core halves together. Scott will look at buying back 1/8 - 1/4 inch for these from the Raft, and James Osborn will look into a more streamlined design for these ties which can be removed from the top, since there will be little room for access from the side.

Alignment System Issues

Keith Jobe made some observation about varying technologies for a real-time alignment system for the Support Tube and Raft.

Stretched-wire system through the Support Tube: this is anchored to the Raft, and can monitor the droop of the carbon fiber Support Tube. It is mildly redundant with the SVT alignment monitors.

Line-of-sight viewing thorugh S.T.: This does not require sensors in the S.T., but cross-hairs which can be illuminated and viewed from a fixed reference outside the S.T. Its absolute accuracy is set by the diffraction of light, which Keith felt could be kept to 250 microns. Relative motion may be easier to monitor precisely.

Water levels on Raft and S.T.: This provides absolute measurement of vertical position. However, water has a fairly large coefficient of expansion, so the temperature and barometric pressure in the level must be held very accurately. The monitors may be fairly large, and must all be mounted at the same elevation.

Camera with light source: A camera mounted in the tunnel could pick up a light source mounted on the S.T., through a lense at the tunnel mouth. This may produce 50-100 micron resolution.

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