Patent ID: 7351965

Claim:
A method for forming a circularly polarized RF field in an electrode structure, the electrode structure including a plurality of main electrodes coaxially disposed about a central axis and extending generally in the direction of the central axis, the main electrodes defining an interior space extending along the central axis, the method comprising: applying a first RF voltage to at least two of the main electrodes; applying a second RF voltage to a compensation electrode disposed in the interior space proximate to a corresponding main electrode at a radial distance from the central axis less than the radial distance of the corresponding main electrode from the central axis; applying a third RF voltage between first and second main electrodes spaced apart along a first axis orthogonal to the central axis; and applying a fourth RF voltage, in phase quadrature with the third RF voltage, between third and fourth main electrodes spaced apart along a second axis orthogonal to the central axis.