Minutes of the IR Engineering and Physics Meeting of 22 Mar 96 Quad Testing John Seeman presented more results from a series of tests on an SSC permanent magnet quad, and a HER Arc quad, with solenoid and mirror plates. SSC P.M. Quad Measurements: Further Hall probe measurements of this quad show that the vertical component of the B-field on the x-axis, just outside the magnet, is symmetric from one end to the other. The peak stray field is 1400 G at the outer collar, in the middle of the magnet length. This drops down to 725 G at the ends on the outer collar, and also drops off quickly with increased radial distance from the quad centerline. Quad with Solenoid: Measurements presented last week showed that the mirror plate with a bore shaped like the quad pole tips did not adequately shield the quad from the external solenoid field. To qualify this, the solenoid axial field strength was measured with a Hall probe through the solenoid and into the quad magnet. When the mirror plate was added, the field in the solenoid increased, as expected, then it dropped off in the entrance to the quad, as some of the axial field was shunted out to the flux plate. However, the axial field only dropped by 40%, indicating that 60% of the axial field entered the quad magnet proper. In another experiment, a single winding was wrapped around each quad pole at its root, so a bucking octupole field could be generated. At 30 Amps, this winding produced a 1 x 10^-4 octupole harmonic in the quad. New, higher precision octupole windings are being made which should be able to produce ten times the bucking field. These should be able to buck up to 300 G of solenoid field. Iron Q2 Update Fran Younger ran a poisson analysis of a possible octupole winding configuration for the iron Q2 design. Because of the tight space constraints from the four septum coils, the octupole windings lie just inside the main coils, where the coils meet the steel of the pole tips. The coils contain seven windings run at 5 Amps. They produce a 4 G octupole field at 4.23 cm (the bore radius of the magnet). This is roughly the octupole harmonic expected from a 100 G solenoid field. In essence, this method is using a non-local correction (octupole windings) to offset a local harmonic problem (octupole on the in-board end of the magnet). This is the antithesis of the P.M. Q2 harmonic correction ring, which has been shown by the Lattice Group to be an acceptable way to cancel harmonics. Since the beta-function is changing rapidly through the magnet, the concern has been that local correction for distributed harmonics can not completely negate their effect on the beam. However, this does not seem to be a problem for the P.M. Q2 correction scheme. Thus, by inference, the octupole windings should also produce acceptable correction (although we will check on this, anyway, with the Lattice Group). B1, Q1 Harmonic Analysis Update Mike Sullivan reported on harmonic analysis for B1 and Q1 permanent magnets. First, harmonic magnitude is more sensitive to the block magnetization angle error than to the error in magnitude. So far, these errors have been modeled as square-wave errors, with constant distribution within the error range. However, recent data from Shin-Etsu shows that for both magnitude and angularity error, the blocks are spread in a gaussian-like distribution. Mike added this error distribution to the MBUILD program, and found that, for the tight sigma shown for the Shin- Etsu material, the harmonics are reduced on the order of 30-50% from the flat-distribution simulations. This is significant because it means we can open up the error tolerance in our procurement specification, knowing that the gaussian distribution of the as-received material will produce better harmonics than the spec values would suggest. MBUILD was then further modified to build variable-radius slices, to better simulate B1 magnet fabrication. Using standard 0.005" dimensional tolerances, and +/- 2 deg and 2%, with a remanent field of 10.5 kG, the magnet strength is exactly what is needed (337.5 kG-m). The 4% margin that had been built into the simplified design of last fall was "used up" by the tolerances and errors. This simulation includes a derating factor to account for a relative permeability of 1.05. For this magnet, the relative harmonic values were 2 x 10^-4 for the sextupole harmonic, and <10^-4 for all other N. The radius of expansion for the harmonic calucation was the BSC at the slice being evaluated. This changes through B1, from a radius of 0.92 cm to 2.0 cm. The intent of using the varying BSC as the radius of expansion was to find a method to compare the relative effect on the beams of harmonics from slice to slice. This method essentially scales the harmonic by the BSC. There was some discussion as to whether this was the most appropriate scaling. The BSC changes with (Beta)^0.5, which defines steering effects of a magnet, but tuning effects vary linearly with (Beta), so this may be a better scaling factor. Mike will look into this. This method of scaling harmonics has an impact on Q1 as well. Although the bore of the magnet is constant, the BSC's are changing rapidly, so the slice harmonics will scale differently, depending on the location of the slice along the magnet. P.M. Quad Update Dave Humphries gave a quick update on the P.M. Q2 shielding design progress. Two concepts for solenoid shielding were presented. One used nested cones in front of Q2 to shunt the stray solenoid field away from the bore of Q2. An active shield could use a single cone, with bucking coils to accomplish the same task. Either configuration must fit within tight space constraints in-board of Q2, where the Forward shielding plug wraps around the Septum beampipe. These minutes, and agenda for future meetings, are available on the Web at: http://www.slac.stanford.edu/accel/pepii/near-ir/home.html