To: Distribution 17 July 96

From: Martin Nordby

Subject: Minutes of the IR Engineering and Physics Meeting of 12 July 96

Hard-Copy Distribution:

Bob Bell	41	Jim Krebs	41
Lou Bertolini	LLNL L-287	Dave Kirkby	95
Gordon Bowden	26	Harvey Lynch	41
Pat Burchat	95	Tom Mattison	17
David Coward	95	James Osborn	LBL B71J
Scott Debarger	17	Eric Reuter	18
Hobey DeStaebler	17	Andy Ringwall	17
Jonathan Dorfan	17	Knut Skarpaas VIII	18
Stan Ecklund	17	John Seeman	17
Alex Grillo	95	Mike Sullivan	17
John Hodgson	12	Uli Wienands	17
Hank Hsieh	LBL B71J	Mike Zisman	LBL B71J
David Humphries	LBL 46-161
Roy Kerth	LBL 50-340

Electronic Distribution:

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

Iron SK1 Update

Fran Younger showed results of 3-D Amperes analysis of the short-core Iron SK1 design. While the 2-D POISSON runs showed good harmonics, they did not include the 3-D effects of the coil turn-arounds. With only two coils, the coil ends only wrap around two of the four magnet poles. This produces a 50% difference between the peak field at the ends of the poles with coils, and those without. Furthermore, since the magnet is so short (12 cm long total length), this produces a 20% difference in the field integral along the length of the magnet. This produces unacceptably large harmonics, which can not be easily canceled.

With these latest results, it became clear that the only viable technology for the SK1 was a rotating permanent magnet array. David Humphries will forge ahead on this design. Most significantly, the space between Q2 and Q4 is still too tight to fit both SK1 and a Harmonic Correction Ring for Q2. David and James Osborn will look at shortening Q2 by 2-3 cm to make the space available, and to block out this space for SK1 and the Har. Corr. Ring.

B1/Q1 Magnetic Design

Mike Sullivan reported on progress towards finalizing the P.M. block geometry for the B1 and Q1 magnets. The baseline B1 design is slightly weak, when all tolerances and clearances are included. Mike added 3.5 mm to the outside radius of the back-end slices to compensate. This radial space comes out of the relatively thick support rings. The B1 baseline design has ÚBdL = 3.3788 kG-m, while the new configuration has ÚBdL = 3.3785 kG-m, for a beam separation of 11.01s at the first parasitic crossing.

For Q1, the magnet is now split into a smaller-radius Q1A which fits around the smaller BSC of the first two-thirds of the magnet, and a larger Q1B at the out-board end of the magnet. Spec's for the magnet are:

Q1A Quad:

R1 = 57 mm (compared with 74 mm R1 for prototype design)

R2 = 88.9 mm

G = -119.23 kG/m (compared with -106.51 kG/m for prototype design)

Q1A Dipole:

R1 = 94.9 mm

R2 = 133.5 mm (4.3 cm smaller than the prototype design)

B = 3.279 kG (increased from 2.13 kG from the prototype design)

Q1B does not have a dipole section, so the quad field is not offset.

This design leaves radial space for a 4% quad trim, and <1% horizontal and vertical dipole trims outside of the dipole section. These trims end up being fairly large, but "copper is cheaper than samarium-cobalt," so this inefficiency is well worth the cost savings in the P.M. material.

In re-configuring the magnets, it became clear that trimming Q1 produces significant changes to the BSC at Q2-Q5. The above configuration accounts for this by providing more dipole than initially considered necessary, to increase separation through these magnets. This also compensated for the 1.5 mm loss of separation at Q5 generated by the longer Q2 magnet. The bottom line is that, at nominal conditions, the beam separation has increased from the previous baseline design by 3.65 mm at Q2, 2.55 mm at Q4, and 0 mm at Q5. If a strength-adjusting ring is added to the back of Q1, this separation will increase somewhat.

The problem comes when the Q1 trims are used. Counter-rotating the back two rings of Q1 for trimming produces significant changes to the beam separation. For a ± 4% trim on Q1, the beam separation at Q2 varies by +0.83 mm / -2.03 mm. At Q4 separation varies by +1.53 mm / -3.72 mm. At Q5 this is +3.24 mm / -11.01 mm (these changes are with respect to the new, increased nominal separations listed above).

The conclusion is that, although the nominal running configuration looks fine, the large variations in separation brought on by trimming Q1 are far to large to be absorbed in the current aperture of the vacuum chambers. Mike will investigate the effects of longer, electro-magnet trims, since they more gradually steer both beams, and should not affect separation as much. Furthermore, the horizontal dipole trim may be able to compensate for the over-steering effect of the quad trim. Mike will look into this.

Stan Ecklund and John Seeman agreed to refine the list of trim requirements for Q1, and develop a more realistic trim range. We agreed on a configuration which included ±1% quad a dipole electromagnet trims, plus manually-rotated P.M. trim rings on the back of Q1 for strength adjustment and trimming for larger-scale machine re-configurations (such as changing asymmetry or beam energies).

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

http://www.slac.stanford.edu/accel/pepii/near-ir/home.html