Admittance probe measurements in the double inverse pinch device

Publisher Website
Google Scholar
Abstract
A floating voltage swept double probe is described and the components of the plasma sheath admittance (Y = 1/R + jωC) are measured as a function of time in argon and hydrogen. The measurements are carried out in the double inverse pinch device (DIPD Mark I), a pulsed device, which generates a quadrupole magnetic field. The probe is swept at 500 kHz with a sinusoidal voltage. Sheath capacitance and resistance are measured at one point in space and at a variety of times following preionization. The plasma sheath parameters are discussed in terms of equivalent circuits which are found to simulate the plasma sheath response. The sheath capacitance is larger than predicted by present theories. Estimates of plasma temperature and density are made from the sheath measurements and are found to be low owing to the theoretical uncertainty in capacitance. With improvement in sheath theory, the technique should give accurate temperature and density measurements in transient plasmas.