The effects of plasma density and magnetic field on ion temperature and drift velocity in a LaB6 direct current plasma

Abstract

In a LaB6 direct current plasma, parallel and perpendicular ion temperatures (Ti∥ and Ti⊥) were measured as a function of plasma density and magnetic field by a laser-induced fluorescence technique. In order to study the impacts of magnetic field and plasma density on ion temperature and drift velocity, the plasma density was controlled by a magnetic field and discharge current under the following plasma conditions: The magnetic field intensity at the measurement position, BD, was 186–405 G; discharge voltage, Vdis, was 29.9–32.1 V; discharge current, Idis, was 10–22 A; neutral pressures, Pn, were 130 mTorr (in the source region) and 2.2 mTorr (at diagnostic region); plasma density, np, was (2–8)×1012 cm−3; and electron temperature, Te, was ∼2.6 eV. Parallel ion temperature (Ti∥), perpendicular ion temperature (Ti⊥), and drift velocity, vD∥ (or drift kinetic energy, ED) all increase as a function of BD and Idis, such that the total ion energy, Et (=Ti⊥+Ti∥+ED), increases as a function of BD and Idis. From the relations of Ti∥, Ti⊥, and vD∥ to np, ion temperature and drift velocity were observed to be strongly depend on plasma density. In consideration of the collision time scales, ion gyrofrequency, and time of flight from the source to the measurement position, the dominant process for ion heating was observed to be the electron-ion collisions, although the magnetic field and ion-neutral collisions contribute to ion temperature anisotropy.