Analysis and measurements of eddy current effects of a beam tube in a pulsed magnet

Abstract

The power supply design of the γ t-jump system in FNAL Main Injector uses a resonant circuit[1]. A critical design parameter is the ac losses of the beam tube in a pulsed quadrupole. This paper gives an analysis to this problem. An equivalent circuit model based on the impedance measurement was established. The measured and calculated losses are in agreement. Another effect of the eddy current is the distortion of the magnetic field inside the beam tube. A Morgan coil was used for field measurements up to 10 KHz. These results are presented in this paper.

Eddy current modeling and measuring in fast-pulsed resistive magnets

“…In general, the main effects of eddy currents are: (i) to screen flux changes, (ii) to delay the achievement of nominal DC field, (iii) to introduce high harmonic content perturbing the field [4]. An equivalent circuit model is necessary to fully understand the eddy currents effects, as well as to plan possible corrective actions [5]- [6]. Eddy current effects are hard to predict accurately because they depend on a number of uncertain parameters, such as the magnetic properties of the iron yoke, its temperature, the surface resistivity of the laminations [7], the mechanical tolerances leading to unwanted air gaps in the magnetic circuit, etc.…”