Loading detection and number estimation of an electron plasma in a penning trap

Abstract

A quadrupole Penning trap for spectroscopy and investigations of non-neutral plasmas was designed and built. In this work we provide details of the trap design and a discussion of a simple design and procedure for convenient electron loading from an aligned filament. Electrons from thermionic emission which form a low-energy diffuse beam are trapped in weak magnetic fields. They are detected through a non-destructive electronic detection scheme, the details of which are discussed. The detection signal is diminished when the electron beam energy is increased while the electron flux is kept constant. This is explained by considering the energy shift in the distribution function of electrons emitted from the filament and entering the trap. We present a calculation of the number of trapped electrons from the shape of the detection signal. This calculation, based on a model of a driven damped harmonic oscillator to describe the axial motion of the electrons, compares favourably with the numbers obtained by measurements of the space charge induced shift in the trap potential.