Minutes of the IR Engineering and Physics Meeting of 21 Jun 96 Iron SK1 Update Fran Younger reported on progress in fitting an iron SK1 into the 121 mm space between Q2 and Q4. The design presented used two coils, with an iron core split-able on the horizontal plane. It is relieved at the split plane to avoid the HEB chamber, and on the LEB out-board side for symmetry. Its total length (core plus coil turn-arounds) is 120 mm, which is 1 mm shorter than the available space. The 2-D Poisson analysis shows a gradient of 1 kG/cm at 5 cm radius, with 5 x 10^-4 level harmonics in the LEB channel. At the centroid of the HEB, the field is 2.7 G, with a gradient across the HEB of 1.5 G/cm. Since the SK1 is so short, this field integrates to much less than the target value of 1 G/m over the length of the magnet. The main coils for this generate 10 kW of power, when running at the design current of 484 Amps, with a 21.5 V drop. Although there is no Z-space to spare on the magnet, Fran felt that there was margin to increase the gradient of the existing design to account for the expected 3-D end-field effects. The 3-D stray fields in the HEB should also be worse than the 2-D simulations suggest, but there appears to be a large margin to account for this, as well. Fran's next step is to run a 3-D analysis of the magnet. Dose Rate Calculations in B1 and Q1 Magnets David Kirkby has used the GEANT-based program BBSIM to simulate backgrounds in the detector. He has used this to simulate the expected radiation dose on the B1 and Q1 Magnets. The model assumes a copper support structure for the Q1 Magnet, a steel Q1 Chamber, an aluminum structure for the B1 Magnet, with a copper chamber, and SmCo magnetic material for B1 and Q1. It also includes the magnetic fields of the detector solenoid, B1, and the hybrid Q1. The expected backgrounds which contribute to radiation damage are lost particles from brem. and Coulomb interactions, and radiative Bhabha scattering. The lost particle events are generated with TURTLE, then tracked through the IP using BBSIM. Radiative Bhabha events are generated using BBREM and tracked through the IP. Synchrotron radiation is not included in the simulation, and is not expected to generate damaging radiation. Track energies were recorded for each block of SmCo material for B1 and Q1, then the blocks were divided into finer radial bins and the tracks re-recorded. With no radial binning, the peak dose in B1 was 120 krad/yr at the back of the Forward B1. For Q1, the maximum dose was 2.2 Mrad/yr on the Backward Q1, outboard end. Since the dose rate falls off quickly as the shower energy is deposited in the material, the radial binning provides a more accurate estimate of peak dose rate. For B1, the peak is 185 krad/yr, but for Q1, the peak is 20 Mrad.yr, 10 times times higher than the average for one block. These peaks are all in the horizontal plane, but assume an average dose over the azimuthal width of the block. The next step for this analysis is to divide the horizontal blocks into finer azimuthal bins, to better determine the size of the shower, and the peak dose. Also, as Hobey DeStaebler discussed last week, the radiation dose is not the ideal figure of merit to estimate radiation damage. What are more relevant are the quantity and spread of energies of the impinging particles. David plans to modify the simulation to record these, as well as to divided the azimuthal bins into finer structure. Radiative Bhabha Strikes Mike Sullivan used MAGBENDS to provide an estimate of the energies of radiative Bhabha's striking Q1. At energies between 2.3 and 0.5 GeV, particles are over-bent in the bend field of the hybrid Q1 and strike the wall of the Q1 Chamber. The higher energy particles strike the out-board end of the magnet, producing the peak dose rate. The incident angle of the particles ranges from 78 to 110 mrads. Radiation Damage Testing A general discussion ensued regarding setting up a test which best mimicked the expected radiation dose, particle rate, and energy. Three possible locations for the test are: 1. the booster-to-SPEAR transport line; 2. somewhere in/around the positron extraction line; and 3. 52SL2 Slit Collimators at the end of the Linac. This has a one-radiation-length spoiler in front of it to protect the collimator. Ralph Nelson felt that the shower energy from the spoiler should be close to the 1-2 GeV needed, and the dose rate fast enough so the test could be run over a few weeks' running time, but not fast enough to require cooling and temperature monitoring. Artem Kulikov and Ralph Nelson will investigate using the positron extraction line or the 52SL2 location on the Linac. Editor's Note Following the IR Meeting, a decision was made to use Sm2Co17 for the B1 and Q1 Magnets. The uncertainties of the effect of radiation on the NdFeB material, and its effect on the magnet performance was deemed too large a risk to take for the sake of saving material costs. Furthermore, since fabrication of these magnets is on the critical path for the LER commissioning, there would not be time to recover from negative results of a radiation tests of NdFeB over the summer. However, David Kirkby's analyses have raised enough concern about the radiation dose for the Sm2Co17, that further simulations, and confirming tests on Sm2Co17 will be considered. These minutes, and agenda for future meetings, are available on the Web at: http://www.slac.stanford.edu/accel/pepii/near-ir/home.html