Radial plasma structure during a theta-pinch implosion: Flute instabilities

Abstract

Flute instabilities have been observed during the implosion of an ≈1×1014 cm−3 initial electron density theta pinch. The flutes occupy only a fraction of the plasma self-luminosity pattern and disappear after formation of the plasma column. The total structure of the luminosity patterns has been correlated with the imploding plasma density and magnetic field distribution.

Method of measuring directed electron velocities in flowing plasma using the incoherent regions of laser scattering

“…To develop a set of general equations illustrating this diagnostic, it is useful to refer to Figure 1. A general expression for the scattered signals P , that holds for electron temperatures up to around 1 keV is [3] P.r 2…”

“…The magnitude and direction of the flow velocity of a plasma can be inferred from such quantities as impact pressure [1] or the position of luminous fronts [2]. However, direct means of measuring this velocity have not been well developed.…”

10.6μm interferometry and Faraday rotation measurements on a θ-pinch plasma

“…Several previous measurements of the electron density of theta-pinch plasmas have been made by end-on ruby laser interferometry (McKenma et al 1974, 1975, Nicholson et al 1970. However, when the plasma length is much greater than its radius one would expect improved spatial resolution with interferometric measurements made across the tube.…”

Integrity of the plasma magnetic nozzle

“…Also, early experiments on theta-pinch implosions were observed in the implosion-onset phase to contain fine-scale radial protrusions around the circumference (McKenna, Ref. 34), but no detailed identification was attempted.…”

“…Therefore, it is reasonable to regard the time constant for imposed field growth as tb t , which is the plasma's transit time through the converging part of the nozzle. Then, the plasma-field mixing layer thickness implied by Equation (33) can be expressed as δ = Dtb t (34) where tb t is the nominal transit time through the converging part of the nozzle, tb t ≈ Lb t Xt . Thus, essentially the same answer is reached for field diffusion into plasma as in Subsection 2.2.2 (assuming β is of order 1) when the plasma diffuses into the field.…”