To: Distribution 4 Dec 96

From: Martin Nordby

Subject: IR Engineering and Physics Meeting Minutes of 22 Nov 96

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	Eddie Lin	17
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

Harmonic Correction Ring Preliminary Design Review

This meeting was dedicated to a Preliminary Design Review for the Q1 and Q2 Harmonic Correction Rings. David Humphries presented advanced conceptual designs for both Rings, with supporting analysis and trade-off studies used for sizing the Rings.

Q1 Harmonic Corrector Ring

The Q1 HCR is clam-shelled around the Q1 Chamber, just outboard of the rotating Q1C Magnet slices. This allows it to be removed to gain access to the neighboring vacuum flange. The two halves of the Ring pin together, then pin to the end of Q1, ensuring good repeatability. The Ring is comprised of 20 elements of SmCo cylinders, 2 cm in diameter on an 8.7 cm radius circle. The elements are epoxied into 0.028 inch thick thin-walled sleeves, which slide into holes in a retaining ring, and are held in place by set screws which bear on the outside of the sleeves. Each element consists of two SmCo cylinders which are placed end-to-end, and can be independently rotated. Each cylinder has a cap glued on its end to rotate it into its correct position, and measure the position. Needed positional error tolerance is 1-2°, but is not very critical, since the tuning method relies on relative, or differential, positioning of the elements, not on their absolute position.

In sizing the Q1 HCR, David investigated the trade-off between number of elements and element size. All options maintained a constant inscribed circle radius of 7.7 cm, which is set by the O.D. of the Q1 Vacuum Chamber. Using a 24-element HCR instead of 32 elements increased correction capacity for lower harmonics by 50%, while only slightly reducing capacity of higher harmonics. The 24-element design can correct 10^-3 harmonics in Q1 for lower harmonics for each 1 cm of element length, while maintaining feeddwon harmonics of order 5 X 10^-6 (at ref radius of 6 cm).

Going to a 20-element corrector increases capacity by an additional 10-20% over the 24-element design for n = 3-5, then shows little affect at higher harmonics. However, feeddown harmonics double for n < 8, putting them near the design limit of 10^-4 of the main quad field.

The final design uses the 24-element configuration, with an expected SmCo material cost of $10k, and a total budget of $106.5k. This assumes a total material length of 8 cm, although the material cost is driven mostly by handling, not actual SmCo cost.

Action Items

We decided to place an order for the Q1 HCR SmCo material. Before this happens, three action items need to be reolved:

--Finalize the element diameter and tube size, given the final 24-element geometry (David Humphries, Al Constable).

--Develop a conceptual design for the Q1C rotating slices, and finalize on the z-space needed. This sets the length for the Q1 HCR, and of the SmCo elements (Andy Ringwall).

--Modify the B1 and Q1 SmCo material spec and cut drawings of the elements (David Humphries).

A subset of the IR group will meet in a few weeks to ensure that these items are resolved, then the RFP will be sent out.

Q2 Harmonic Correction Ring

The Q2 HCR uses 24 elements of 1.3 cm diameter, on a 5.95 cm radius circle. The clam-shell design will be similar to the Q1 HCR design. At a reference radius of 4.5 cm, the capacity is 5 X 10^-3 per cm of element length for harmonics n = 2-10. Feeddown harmonics are in the 5-10 X 10^-5 range, per cm of element length. The current length of the corrector elements is 4.5 cm, which barely fits between the SK1 envelope and the back of Q2.

David investigated increasing the circle radius of the elements from 5.95 to 6.2 cm, to reduce feeddown harmonics. This dropped capacity by 10-20%, without significantly reducing feeddown harmonics. Since this design is squeezed for space, overall capacity is a concern, so David opted to stay with the smaller radius design to maximize capacity.

Since the Q2 HCR is a "septum magnet", David looked into stray fields which could affect the HEB. A 2-D Pandira model of the HCR tuned to a quad field shows that the field drops off quickly outside the magnet array. David plans to surround the HCR and SK1 with a 2 mm thick iron cylinder, which eliminates all stray field in the HEB passage due to the HCR (results show 1-2 G, which is less than the accuracy of the model).

Assuming a permeability of 1.05, the iron shield reduced the quad strength by 1%, with no apparent impact on the field quality. This shows that putting the HCR inside the SK1 shield cylinder will not affect its performance.

David also built a 3-D Amperes model of the HCR and the Q2 iron core to investigate the effect of the neighboring iron core to the HCR performance. Tuning the HCR to a sextupole, and integrating resulting harmonics through Q2 and the HCR shows that the iron reduces the n = 3 field by 5%. David thought that this 5%-level of reduction would be expected for most harmonics. James Osborn said that n = 10 and 14 are the Q2 harmonics most likley to need tuning, so David will re-run the model, with the HCR tuned to these harmonics.

This design is now fairly mature, but it can not be finalized until the end of Q2 and the SK1 magnet are finalized. The plan is to focus on building a first-article Q1 HCR, while the Q2 area is finalized, then go back and clean up the Q2 HCR design and build it.

HOM Analysis of Near IR

Eddie Lin gave an update on the HOM analysis of the Near IR. When last we heard from him, he reported that the gradual tapers in the B1 vertical masking trapped TE modes which were produced by the big horizontal mask.

To modify the masks, on the incoming LEB side, Eddie carried the smallest bore cross-section through to the Vertex Vaccum Chamber. This produces a longer, vertical constriction which serves to hide the horizontal mask. On the incoming HEB side, he did just the opposite, changing the gently sloping vertical mask into a sharp, 1 cm thick iris. This allows the modes to escape.

The new geometry dramatically reduces the TE11 modes produced in the Vertex Chamber. The TM01 and TM21 modes are bigger factors, but the total power produced is 25% of the original design. This has been done by reducing Q(external) significantly. For one 3 amp beam, key resonance values are:

TM011: Q = 4000 P = 115 watts

TE111: Q = 3600 P = 8 watts

TE211: Q = 8000 P = 102 watts

Maximum possible power dissipated, assuming all beam HOM's are lit up, is 200 watts. For modes which are symmetric about the I.P., dissipated power increases by 4X when both beams are included. For anti-symmetric modes, the modes cancel, and power dissipated is zero. To assume the worst case, plan on 100 watts of maximum possible power in the Vertex Vacuum Chamber. This assumes that all modes are on resonance, and all are symmetric about the I.P.

This design seems to be very conservative, which is good, since the chamber is buried so deeply inside the detector. Martin floated the idea of looking into reducing expected power so gas cooling could be used. However, Eddie said that this would require a factor of 4 decrease in Q(external), which he thought would be very difficult. The working conclusion is to stay with water cooling, leave no provision for gas cooling, and plan on the 1000 watt max power value.

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

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