Multi-mass filter

Abstract

A multi-mass filter for separating particles according to their mass-charge ratio includes a chamber for receiving a multi-species plasma that includes particles therein having different mass-charge ratios (with M,<M,<M,). Inside the chamber, which defines an axis, a radial electric field is crossed with a magnetic field (E&lE;B) to move the particles (M,, M,and M,) on respective trajectories into respective first, second and third regions. For one embodiment, the filter is configured so that a,B,is held constant in the expression for cut-off mass, M,&equals;ea,B,/(8V,). For this embodiment, only the heavier particles M,are ejected into the third region (M,>M,) and only the intermediate particles M,are ejected into the second region (M,>M,). In another embodiment, the radial electrical field is increased outwardly from the axis to a radial distance a,(r,) at a first rate. The electrical field is then increased radially outward between a,(r,) and a radial distance a,(r,) at a lower rate. This electric field configuration defines the first region between the axis and a,(r,), and the second region between a,(r,) and a,(r,). The third region is located radially beyond the second region. Accordingly, with M,&equals;er,B,/(8*(V,V,)) and M,&equals;e(r,&minus;r,)B,/(8*V,), particles M,are confined in the first region, while both particles M,and M,are ejected from the first region into the second region. The particles M,are, however, confined in the second region and only the particles M,are ejected from the second region into the third region.