Shielding of the CBETA electron dump
The initial shielding of the ERL dump was described in a note ”Notes on CBETA Dump Shield” dated March 5th, 2019. In that note the primary concern was to minimize the radiation downstream from the dump as the electron beam entered the FFAG arc on the East side of LOE. Accordingly, the entrance into the dump in LOE was not shielded. In retrospect this was a mistake as it was found that radiation emitted by the dump in the ”upstream” direction into LOE causes gamma radiation monitors to set off at electron currents > 10µA. Also, the actual shielding configuration in the previous note does not reflect the actual shielding as implemented and the calculations described below take this into account and include addition shielding at the entrance to the dump that was not present in the previous note.