Implementation of moiré-schlieren deflectometry on a small scale fast capillary plasma discharge

We present the results of an implementation of a refractive diagnostic to study fast dynamics in capillary discharges. It consists of a moire-schlieren deflectometry technique that provides a quantitative analysis of the refractive index gradients. The technique is composed of an angular deflection mapping system (moire deflectometry) and a spatial Fourier filter (schlieren). Temporal resolution of 12 ps, 50 μm of spatial resolution and minimum detectable gradient of ( ∇ n e ) min = 6 × 10 18 cm - 4 were obtained. With these parameters, a large aspect ratio capillary discharge of 15 ns half period current was studied; the diagnostic was implemented axially along the alumina tube of 1.6 mm inner diameter and 21 mm length. The detectable electron density for these conditions was 1 × 10 17 cm - 3 . From the interpretation of the fringe displacement, we are able to measure the velocity of the radial compression wave and the compression ratio due to the Lorentz force. On axis, electron densities of the order of 5 × 10 17 cm - 3 were obtained at the time of maximum soft x-ray emission.