To: Distribution 25 Aug 95 From: Martin Nordby Subject: Minutes of Near IR Engineering Meeting of 25 Aug 95 Q1 Cross-Section Layout Joe Stieber showed a revised layout of the Support Tube through Q1. This incorporated a few key changes to the design, as well as some more mundane ones (you choose which is which): 1. Per the decision of the "BaBar Dimensions Committee," the outside radius of the Support Tube grew by 10 mm to 225 mm. The Drfit Chamber inside radius also increased by the same amount, so the clearance betweeen the two is still 10 mm. 2. Tolerances for the Q1-Quad and Q1-Dipole slices were refined from the lump 10% allowance to 8%. Thus, the design is 8% stronger than theoretically needed to account for losses in field strength from gaps, and lower as-built remnant field strength. This reduction in overage of 2% saved 2 mm in the outer radius of the dipole. 3. 5.5 mm were reserved for "magnetic" shims outside the dipole slice. These will be used to trim the magnet slices, thereby reducing the multi-pole content of the field. 4. The SVT signal cables were stacked 6-high, requiring 1.5 mm more radial space, but resulting in significantly more azimuthal space. 5. Shielding could be provided for the SVT signal cables, if needed, by boxing them in a 0.006" thick copper-clad kapton box. 6. Alignment wires for the Support Tube were added, and the redundant purge lines removed. Fred Goozen and Joe Stieber will work on refining the SVT cable positions to even out their azimuthal coverage. One of the few remaining issues regarding the Support Tube interface with BaBar is the expected earthquake motion between the Tube and the Drift Chamber. Les Dittert is working on trying to reduce the +/- 18 mm lateral motion of the DIRC tube/D.C. on the forward end with no seismic isolators on BaBar. He will report on this next week at the BaBar Integration meeting. Magnetic Inspection Zach Wolf presented the proposed plan for inspecting and measuring the permanent magnet blocks and assemblies. The agreed-on measurement accuracy criteria are: Block Remnant Field Measurement: Magnitude: 0.1% Direction: 0.1 degrees Temp: known to 0.1 degrees C Assembled Magnets: Int(BdL): 0.02% Int(GdL): 0.02% Harmonics: 0.01% (at a radius to be determined) These values are similar to those used in measuring similar magnets elsewhere. There was some question as to how stable the room temperature must be when performing measurements. This will be investigated. Helmholtz coils will be used to measure the block magnetization. They measure flux by integrating the voltage induced in the coils by the block. This will determine the magnitude and direction of the magnetization. The coils will be 1 m diameter, with 3000 turns per coil. Prototype testing will show what effect the motor and other magnetic material has on the accuracy of the measurement. These coils should be operational by late September, and fully working by mid-October. The slices will be measured by rotating bucking coils. The two rotating coils are in the same plane and connected in series, but have different radii and number of windings. This cancels out the main field component of the magnet, and allows higher precsion measurements of the multi-pole fields. This should be operational in 3 months. Q1 Remnant Field Hobey DeStaebler presented an eclectic collection of data about the magnetization of the permanent magnets. First, per the M-H graphs of the manufacturer, the magnetization of the P.M. decreases as the external field grows. The rate of decrease is apparently linear, with a slope -0.56% for Shin-Etsu R-26HS, and -0.31% for Crucible Crumax 3125. These rough values raise more questions than they answer: does the material really behave linearly? Is this effect reversible? Does the material "creep" magnetically, by losing magnetization over time, when sitting in an external field? M. Nordby is working with some of the manufacturers to get answers (in the form of hard data) to these questions. Next, because the P.M. material de-magnetizes (austensibly reversibly) in an external field, different blocks of the quad will de-magnetize by different amounts, depending on their field orientation and their position in the radial solenoid field. Hobey showed that this should produce a main quad harmonic in the field, so it should not impair the primary quad field quality. Finally, he showed curves of the magnetization of Sm2Co17 and NdFeB material as a function of radiation dose (from a test done at the Naval Postgraduate School).. At the Grad level, the SmCo clearly held up better than the NdFeB material, but there was quite a spread in the data, and actual trends could be subject to creative curve-fitting to skew the results. Nonetheless, the SVT is very sensitive to radiation, at the Mrad level. This was in the noise of the test data for the P.M. material. Thus, NdFeB probably would be acceptable from a radiation standpoint, if some of its virtues turned out to be needed for Q1. Along that line, Mike Sullivan is studying the possibility of just removing 20 cm of the backward Q1 to eliminate the de-magnetizing problem. The quad would then be strengthened on its in-board end by reducing the inner radius. More on this option nest week.