Electron Cyclotron Resonance Magnetometry with a Plasma Reservoir

Measuring the magnetic field strength in a Malmberg-Penning trap is of direct interest to non-neutral plasma experiments. The magnetic field strength determines the cyclotron frequency of constituent particles, how the number density relates to the plasma rotation frequency, and how quickly the plasma cools. To measure the magnetic field in the Berkeley electron plasma experiment, we expose plasma to microwaves to heat electrons and study the resulting plasma temperature as function of the microwave frequency. The observed heating curves have a resonant structure which depends on the axial bounce frequency and the rotation frequency of the plasma as well as the magnetic field. By understanding this dependence we identify the peak corresponding to electron cyclotron resonance, providing a measurement of the magnetic field to an accuracy of 30 parts per billion. To scan microwave frequencies, we develop a method of quickly preparing low density electron plasmas for destructive temperature measurement. This method involves drawing low density target plasmas from a reservoir. This technique was developed for use in the ALPHA experiment at CERN, where it will be used to improve gravity and hyperfine structure measurements of antihydrogen.