Studies of the effects of non-linear materials in the CREX septum magnet using finite element analysis simulations

Abstract

The CREX experiment measures the 48Ca neutron radius using an electroweak probe. To run the experiment after PREX-2, which measures the neutron radius of 208Pb with the same electroweak parity violation technique, without a configuration change of the equipment, the septum magnet needs to meet field requirements suitable for CREX. As the magnet is iron-dominated the field response is non-linear at sufficiently high current. This is of particular concern for CREX which is run at a beam energy more than double that of PREX-2 and requires a large septum current to provide the specified bend radius. To determine it's suitability in the experiment the magnet non-linearity must be characterized. To that end, the magnetic flux density was simulated using finite element analysis software and was analyzed in the high-field regions and the zero-field region of the septum. In this thesis I will show evidence of magnetic saturation in the septum magnet at the CREX current and that the requisite field strength can be attained in the magnet gaps. I will also show that the proposed upstream and downstream extensions of the beam pipe shield reduce the maximum fringe field strength by more than 80% and provide a factor of 10 improvement to the maximum field integral inside the beam pipe region.