Calculations of the radiation doses to the electronic equipment and magnet coil insulation in the PEP-II tunnel

The PEP-II collaboration is a new physics project at SLAC that utilizes an existing tunnel to house two accelerator storage rings; a low-energy positron ring (4 GeV, called the LER) atop a high-energy electron ring (10 GeV, called the HER). Both rings are being designed to permit a high circulating current of 3 A, corresponding to a beam particle number of 1.38 × 1014. Dose calculations were made to estimate the potential for radiation damages to the electronics and magnet coil insulation in the arc section of the tunnel. An analytical code, SHIELD11, was used to calculate the dose from photon and neutron radiations resulting from beam losses in various modes of operation. Several EGS4 Monte Carlo user codes were developed to calculate the dose from the synchrotron radiation escaping the vacuum chamber in stored beam mode. Two different LER vacuum chamber designs were studied: a 0.35-cm-thick copper wall chamber and a 1-cm-thick aluminum wall chamber with a copper absorber 6 m downstream of every dipole to absorb the synchrotron radiation in a local spot. The HER has a 0.5-cm-thick copper vacuum chamber. Shielding from the 5.4-m-long, C-shaped iron bending magnet for the HER was considered for the beam radiation, while no other structural shielding was assumed for the LER. Furthermore, the dose from all radiations scattering back from the tunnel concrete wall were also estimated using the albedo method or the MORSE code. The results of the dose estimations are presented.