Multi-mass filter

摘要

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 M1 < M2 < M3). Inside the chamber, which defines an axis, a radial electric field is crossed with a magnetic field (E x B) to move the particles (M1, M2 and M3) on respective trajectories into respective first, second and third regions. For one embodiment, the filter is configured so that az2Bz is held constant in the expression for cut-off mass, Mcz = eaz2Bz2/(8Vctr). For this embodiment, only the heavier particles M3 are ejected into the third region (M3 > Mc3) and only the intermediate particles M2 are ejected into the second region (M2 > Mc2). In another embodiment, the radial electrical field is increased outwardly from the axis to a radial distance a2 (r2) at a first rate The electrical field is then increased radially outward between a2 (r2) and a radial distance a3 (r3) at a lower rate. This electric field configuration defines the first region between the axis and a2 (r2), and the second region between a2 (r2) and a3 (r3). The third region is located radially beyond the second region Accordingly, with Mc2 = er22B2/(8*(Vctr-V2)) and Mc3 = e(r32-r22)B2/(8*V2), particles M1 are confined in the first region, while both particles M3 and M2 are ejected from the first region into the second region. The particles M2 are, however, confined in the second region and only the particles M3 are ejected from the second region into the third region.