Eddy currents induced in a muon storage ring vacuum chamber due to a fast kicker

摘要

The goal of AGS E821 is a precision measurement of the muon magnetic moment (g-2) value to 0.35 ppm. A problem with muon injection is the effect of the residual magnetic field during the measurement period due to the eddy currents in the vacuum chamber induced by the kicker pulse. The paper presents a mainly analytical look at the nature of the eddy currents as an equivalent RL circuit and describes a method to solve 2D Maxwell's operations under pulse excitation with some quantitative estimates of the decay time constants. Analysis of the results show that the field due to eddy currents is dependent on the chamber dimensions, type of material, and duration of pulse rise, flattop and fall. The field created by the rising edge of the waveform is largely canceled by the falling edge, providing the pulse is short compared to the diffusion time of the eddy current. The simulation results agree with the theoretical analysis and confirm the residual integral field at the start of the measurement period is acceptable.