Measurement Procedure and Simulation of Permanent Magnet Degradation Due to Electron Beam Radiation*

The Continuous Electron Beam Accelerator Facility at Jefferson Lab currently operates at an energy of 12 GeV. A planned upgrade seeks to use permanent magnets in a new beam line to bring the energy to 22 GeV. This new beam line would accelerate electrons using a Fixed Field Alternating Gradient (FFA) arc, made of permanent magnets in a Halbach-style array. Due to the high levels of radiation in the beam enclosure during operation, the potential degradation of permanent magnets from synchrotron radiation needs to be studied to ensure the success of the FFA upgrade. Different grades and arrangements of NdFeB and SmCo permanent magnet samples will be placed in the beam enclosure along with dosimeters to measure radiation exposure and magnet degradation as part of a Laboratory Directed Research and Development (LDRD) grant. The aim of this project was to create a precise and repeatable procedure to record any demagnetization of these permanent magnet samples using a Helmholtz coil to measure magnetic flux and moment. Different units, ranges, and drift correction settings were tested on the fluxmeter connected to the Helmholtz coil to minimize error and drift. Various recording methods including rotation of single magnet samples and magnet arrays inside the Helmholtz coil were performed. The software BDSIM was utilized to simulate the amount of synchrotron radiation the magnet samples may be exposed to. It was found that demagnetization would be best measured as magnetic moment change in Weber-Centimeters as a function of radiation dose. To measure the samples, they will be removed from their assemblies, and inserted into Helmholtz coil such that a rotation will yield a positive flux measurement. The samples will be rotated quickly, maximum flux will be recorded, and they will be quickly rotated back so that the flux reading is below the 1% drift correction threshold to minimize error. This procedure will be used in the completion of the LDRD to measure all of the magnet samples within the beam enclosure during scheduled accelerator downs and maintenance periods.