Practical considerations for a plasma neutralizer

Publisher Website
Google Scholar
Abstract
A beam of energetic H− or D− ions is efficiently converted to the uncharged state upon impact on a dense plasma. Neutralization efficiencies of the emerging beam can exceed 80%. This paper reports on a design approach to a plasma‐stripping cell, illucidating several practical aspects. The plasma is formed by a low‐frequency (1.4 MHz), high‐power (20–60 kW) rf discharge in a multipole ring‐cusp magnetic field. A mild steel rectangular box is used as a low‐reluctance return path for the magnetic flux, a heat‐transfer medium, and mechanical support. The working gases used in these studies are H2, He, Ar, and Xe. The central density found in the resulting plasma ranged from about 101 3 to ≳101 4 cm− 3 with the heavier species exhibiting the higher densities. Test results performed over a pressure range of 2–10 mTorr are presented. The rf power required to achieve a given plasma density with this design should scale with the cell length for a given gas. Measurements of magnetic‐flux‐density components in the plasma cell volume occupied by the beam path yielded results that are in good agreement with previous calculations. A two‐axis Hall probe is used to measure the magnetic field in two planes, separated by a distance of 1 cm and extending 7 cm beyond the beam entrance, over one quadrant of the beam path. Using these measurements, we produce surface plots of the components and modulus of the magnetic flux density, as well as the projection of flux contours onto their respective planes. The magnitude of any magnetic‐field component is <15 G and also the modulus of B is <15 G in the path of the beam through the cell. The magnetic field at 0.5 cm from the internal copper wall measures ≳1.5 kG, while only 1.4 G is found at the same distance outside the box.

This publication has 0 references indexed in Scilit: