Magnet power supply regulation comments: 240 kW and 500 kW magnet power supplies

Abstract

This note is written for users who need better than about 100 ppm regulated magnet fields in electromagnets. A magnet excitation current regulation of 100 ppm is generally specified to obtain this field regulation, but there are many other variables, in addition to magnet excitation that can change the magnet field. The effects of these other variables are often overlooked or underestimated. If things do not work out, the power supply often gets blamed. A field regulation of 100 ppm requires that the power supply regulates substantially better than 100 ppm and that the effects of other variables are limited. Before we can talk about regulation we must define what regulation is. Power supplies can be regulated for current or voltage. We will only talk about current regulation, since that is the regulation mode used to establish precisely regulated magnetic fields in electromagnets. It is assumed that the same current value will always produce the same corresponding magnetic field value. Later on we will discuss that this assumption is not correct.