A cusp filter for altering a multi-species plasma to separate ions of different masses (M.sub.1 and M.sub.2) includes first and second axi-symmetric magnetic fields which are coaxial, have the same magnitude (B), and are oriented back-to-back to establish a null cusp. The null cusp is thus oriented perpendicular to the axis between the magnetic fields. An injector is provided for directing the plasma ions along the axis toward the null cusp to divert the ions (M.sub.1) away from the axis and prevent them from crossing the null cusp, while allowing the ions (M.sub.2) to cross the null cusp and proceed along the axis through the filter. In one embodiment, a cut-off mass, M.sub.c, is determined such that M.sub.1 <M.sub.c <M.sub.2 with M.sub.c =e.sup.2 B.sup.2 r.sup.2 /2W where "e" is the ion charge, "r" is the radial distance of the ion from the axis, and W is its kinetic energy. In another embodiment, ions of selected mass are heated by cyclotron resonance to raise their energies above that of other ions in order to assure their passage through the null cusp. The selected ions then pass through the null cusp for separation from the other ions.

A linear plasma mass filter includes a container which is shaped as a rectangular prism. Magnetic coils encircle the container for generating a uniform magnetic field (B) in the container, and electrodes are mounted on the container for generating an electric field (E) in the container. Specifically, the electric field is rectilinear in that all of the electric field lines are parallel to each other. Further, the electric field is oriented perpendicular to the magnetic field to create crossed electric and magnetic fields (E.times.B). A plasma source is provided for injecting a multi-species plasma into the container which includes relatively low mass particles (M.sub.1), and relatively high mass particles (M.sub.2). Both M.sub.1 and M.sub.2 are responsive to the magnetic field with respective cyclotron orbits of a first diameter (D.sub.1) and a second diameter (D.sub.2). A first collector is positioned in the container at a projected distance d.sub.1 from the plasma source for collecting the relatively light mass particles (M.sub.1) and a second collector is positioned in the container at a projected distance d.sub.2 from said plasma source for collecting the relatively high mass particles (M.sub.2). For the present invention: d.sub.1 <D.sub.1 <d.sub.2 <D.sub.2.

A device for separating high-mass ions (having cyclotron frequency .OMEGA..sub.h) from low-mass ions (having cyclotron frequency .OMEGA..sub.l) in a plasma includes a chamber. Coils are provided to generate a substantially uniform magnetic field in the chamber. An antenna is provided to launch a left-hand elliptically polarized electromagnetic wave into the chamber along the stationary magnetic field that is evanescent in the multi-species plasma. Importantly, the E vector of the elliptically polarized electromagnetic wave rotates at a frequency, .omega., where .OMEGA..sub.h <.omega.<.OMEGA..sub.l. Ponderomotive forces are generated by the electromagnetic wave that cause the low-mass ions to move toward the antenna while causing the high-mass ions to move away from the antenna.

A system and method for removing plasma contaminants from a vacuum vessel requires circulating a fluid through the vacuum vessel and thereby exposing the fluid to the contaminants. When the contaminants contact the fluid, they are trapped and become suspended in the fluid. The contaminants are then removed from the vacuum vessel along with the fluid. Subsequently, the contaminants can be removed from the fluid, and the fluid reintroduced into the vessel for the subsequent removal of additional contaminants. For one embodiment, a cleaning plasma is generated in the vacuum chamber which interacts with the contaminants to create neutrals. The fluid is then circulated through channels that are formed into a tray which is inserted into the bottom of the chamber. The neutrals then fall into the fluid on the tray, while magnetic shields prevent the cleaning plasma itself from doing so. In another embodiment, the vacuum vessel is an open-ended, hollow, cylindrical centrifuge which is tilted from the vertical. The fluid is then poured into the upper end of the cylinder as it is rotated to allow the fluid to coat the wall of the vessel. For this embodiment, the ions of high mass contaminants are driven from the plasma by centrifugal force and are caused to become trapped and suspended in the fluid at the vessel wall. The suspended contaminants are removed with the fluid at the bottom end of the cylinder.

A plasma mass filter for separating low-mass particles from high-mass particles in a multi-species plasma includes a substantially cylindrically shaped barrier surrounding a chamber and defining a longitudinal axis. Helically shaped coils are mounted on the barrier to establish a magnetic field in the chamber. Conducting rings are provided to establish a radially directed electric field in the chamber. The plasma is injected into the chamber for interaction with the electric and magnetic fields, placing the high-mass particles onto trajectories rotating about a guiding center that travels within a surface having a hyperbolic shape. The low-mass particles are placed onto trajectories rotating about a guiding center that travels within a surface having an elliptical shape. The fields create an axial force directing the particles away from the injection point. As such, the high-mass particles strike the inner wall of the barrier, while the low-mass particles transit through the chamber.