Diagnosing turbulent density fluctuations in Ne and Ar gas-puff Z-pinch implosions

Imploding Ne and Ar gas-puff Z-pinch plasmas on the 1 MA, 220 ns rise time COBRA pulser are studied with the primary focus being the turbulent non-thermal component of ion kinetic energy. Close to stagnation time, spectroscopic studies have shown that turbulence provides a physically sound picture,¹ and accounting for variation in flow velocities yields better fitting results when analyzing Thomson scattering data.² Additionally, recent research³ has demonstrated that this velocity distribution term is inconsistent with laminar velocity gradients and is likely indicative of turbulence.

In this research, a recently developed Imaging Refractometry scheme,⁴ which is a version of Schlieren imaging, is applied to obtain the spectrum of angular deflections of a laser beam propagating through the imploding plasma. Moreover, a method to establish a one-to-one mapping from deflection angle to k-space enables the analysis of the power density spectrum at many different positions along the radial direction. This spectrum is associated with the microscopic density fluctuations in the plasma and hence provides additional information related to the turbulent ion kinetic energy. Results from this diagnostic will be presented.