Time-synchronized Ion Velocity Measurements in Oscillating Plasma Discharges

Christopher Young, Stanford University

Laser induced fluorescence (LIF) velocimetry is a powerful non-intrusive technique for determining ion velocity distribution functions in a wide range of plasma devices using the measured Doppler shift of a particular spectral line. When synchronized with forced or naturally occuring oscillations in the plasma, this LIF diagnostic reveals rich detail about ion dynamics and basic physical processes occurring in the plasma that a time-averaged measurement cannot resolve.

We demonstrate two time-resolved LIF techniques using the Xe II 5d[4]_{7/2} - 6p[3]_{5/2} (834.72 nm air) xenon ion and Xe I 6s[1/2]_{1} - 6p[3/2]_{2} (834.68 nm air) xenon neutral transitions. Excited-state xenon neutral dynamics in a 60 Hz AC xenon discharge are measured and validated using a collisional-radiative model that tracks the energy flow between ground and excited neutral states and the continuum. We also obtain time-varying ion velocity distribution functions in an E×B accelerator, revealing complex fluctuating plasma potential and electric field structures in the device.

Abstract Author(s): Christopher V. Young, Andrea Lucca Fabris, Mark A. Cappelli