Guiding center simulation of rf drift pumping in Phaedrus-B

Rf drift pumping in Phaedrus-B is investigated by numerical simulation of ion orbits. The magnetic field is computed using the paraxial approximation; a simple model is used to approximate the oscillating electric and magnetic fields due to the antennae. Axial and radial ambipolar potential gradients are included in the model. We find that the principal pumping mechanism is the E x B drift motion. The pumping rate increases as the amplitude of the rf fields is increased. Both the bounce and the azimuthal drift resonances contribute to the pumping rate; the azimuthal drift resonance is the dominant effect, particularly at low ion energies. The computed pumping rate compares favorably with the charge exchange rate for rf fields near the limit of that achievable experimentally