A plasma mass filter using a helical magnetic field for separating low-mass particles from high-mass particles in a multi-species plasma includes a cylindrical outer wall located at a distance “a” from a longitudinal axis. Also included is a coaxial cylindrical inner wall positioned to establish a plasma chamber between the inner and outer walls. The magnetic field is generated in this chamber with an axial component (Bz) and an azimuthal component (B&thgr;), which interact together with an electric field to create crossed magnetic and electric fields. The electric field has a positive potential, Vctr, on the inner wall and a zero potential on the outer wall. With these crossed magnetic and electric fields, a multi-species plasma is moved through the chamber with a velocity, vz, high-mass particles in the plasma (M2) are ejected into the outer wall and low-mass particles (M1) are confined in the chamber during transit of the chamber to separate the low-mass particles from the high-mass particles, where M1