Negative ion filter

Abstract

A plasma filter for separating positive ions from negative ions in a multi-species plasma includes a cylindrical shaped chamber. Magnetic coils surrounding the chamber generate a magnetic field that is aligned substantially parallel to the chamber's longitudinal axis. An electrode generates an electric field that is substantially perpendicular to the magnetic field to create crossed magnetic and electric fields inside the chamber. The inward directed electric field has a negative potential on the longitudinal axis and a substantially zero potential at the wall of the chamber. An injector injects the multi-species plasma into said chamber to interact with said crossed magnetic and electric fields. With the chamber wall at a distance “a” from the longitudinal axis, a magnitude “Bz” for the magnetic field, a negative potential for the electric field of “Vctr” along the axis and a substantially zero potential at the wall, a cut-off mass to charge ratio is calculated Mc/e=a2(Bz)2/8Vctr, such that negative ions having a mass M1(−)/e greater than Mc/e will be ejected from the chamber for collection off the chamber wall, while all positive ions will be confined in the chamber for transit through the chamber for collection outside the chamber.

Dependencies are inferred from the claim text.