Measurements of Plasma Jet Velocity in Conical Wire Arrays Z-pinches Using Collective Thomson Scattering*

To characterize the axial propagation velocity of a plasma jet emitted by a conical wire array and its dependence on the aperture angle of the conical array, Thomson scattering measurements were conducted. Plasma jets emitted by conical wire array Z-pinches have been extensively studied as a controlled laboratory setting to study plasma outflows from newborn stars in the form of Herbig-Haro objects in astrophysics. One of the key parameters to evaluate plasma collisionality is the propagation velocity of it, since mean free path has a strong dependence on this quantity (~v^4).

The plasma jet is produced by a conical wire array Z-pinch consisting of 16 wires (50 μm diameter each) acting as the load for the Llampudken pulsed power generator (~400 kA, ~350 ns). To study the variation in the propagation velocity of the plasma jet as a function of base angle of the cone, specifically 20°, 30°, and 40° inclination angles from vertical.

The primary diagnostic tool used was collective Thomson scattering provided by a 1J, 5ns FWHM Nd:YAG laser, connected to a Czerny-Turner spectrometer coupled with a 4QuikE ICCD camera. Spatial resolution is achieved using a linear optical fibre bundle, resolving the axial direction of the jet. Our experimental results show that for all different inclination angles, the propagation velocity variates with the axial position, increasing as it approaches to the upper part of the jet. This result agrees with several numerical simulations, providing an accurate experimental benchmark. Our results also show that jet velocity increases with the base angle of the conical configuration. Further details, potential applications, and results from complementary diagnostics, such as optical spectrometry and Moiré Schlieren deflectometry, will be presented and discussed.