Maintenance for High-Time

Changes to the magnet cryostat requested by (SK) and built by Precision Cryogenics is a larger bore (64 mm diameter), two (instead of one) bolt patterns on each face and no O-ring grooves. We received the magnet in January 2009 and proceeded to test, map and shim the field to improve the homogeneity. The test results are summarized below: 1) Magnet must have been turned around by 180 deg relative to what is used to be before the repair. To maintain the field direction needed for M15 the power leads were reversed at the cryostat. 2) Along the bore (z-axis) the magnetic center line is 2.5 mm below the geometric center line. HiTime should be mounted with the geometric center 2.5 mm above the beam so the beam is injected along the magnetic center line. 3) The magnet is twisted by 0.7 deg (see attached figure). Flanges will be built to correct this twist, then the magnet has to be moved 1.1 mm east to bring back the magnetic center to the center of the beam. 4) The best homogenous field is 3 mm south (toward the cryostat) of the geometric center. 5) Magnetic shims were optimized at 4.5 T by NMR. The metal strips are Netic S3-6 alloy from Magnetic Shield Corporation. The strips are 0.77 inch wide 1.76 inch long and 0.030 inch thick, they and are placed 2 inch apart on both sides of the magnetic center. The rotation of the shims in the bore is very important. Looking from the direction of the beam the center line of the shims should be 35 degrees below the horizontal line and toward the right (i.e. west in M15).