Electron density and ionization dynamics in an imploding z-pinch plasma

Abstract

The time-dependent radial distributions of the electron and ion densities during the implosion phase of a gas-puff z-pinch plasma are determined from measurements of continuum radiation, as well as time-dependent collisional-radiative analysis of the observed particle ionization history in the plasma. It is shown that during the 140-ns-long time interval close to the end of the ϳ620-ns-long implosion phase, the total imploding-plasma mass increases by ϳ65%, found to be consistent with the continuous ionization of the gas ahead of the plasma shell. Furthermore, the densities obtained, together with the previously determined radial distributions of the electron temperature, magnetic field, and particle radial velocities, are used to analyze the energy terms that support the radial propagation of the ionization wave seen in the plasma, thereby explaining the time-dependent radial distribution of the ion charge states in the plasma.

Plasma imaging and spectroscopy diagnostics developed on 100-500-kA pulsed power devices

“…In order to minimize the experimental uncertainties in the observed intensities, the data for each line were averaged over five to eight experiments, and two to four population ratios for each charge state were used. In the C-R analysis, the ratios were calculated for several values of , and the range of chosen was based on continuum radiation measurements [51]. As an example, we present in Fig.…”

“…This plasma region was found to be the hottest and most dense part of the plasma. In this example, was determined both using population ratios within one charge state, and using ratios of levels from successive charge states, the latter with the proper detailed analysis [51], providing a higher accuracy.…”

“…Using the electron temperature obtained, together with the known time-dependent radial distributions of the ion directed velocities [47], magnetic field [6], and electron density [51], all the energy and momentum deposition and dissipation terms in the plasma were calculated, allowing for a comparison between the magnetic energy delivered to the plasma to the energy acquired and dissipated by the plasma. The purpose of the energy-balance analysis is both to quantitatively determine the conversion efficiency of the capacitively stored energy into the kinetic energy of the plasma and to examine the consistency of all the results obtained for the plasma under study.…”

Doppler measurement of implosion velocity in fastZ-pinch x-ray sources

“…Measurement of velocity is important to inferring the plasma kinetic energy, which can be the primary storage reservoir of j × B work accumulated over ∼100 ns during implosion and then provide plasma heating when thermalized at stagnation. While some studies have shown consistent energy balance between kinetic energy input and radiated output [15][16][17][18][19], others have proposed that additional physical processes may provide further plasma heating [20][21][22][23]. Doppler velocity measurements will help to test models and address this key physics issue for high-current pinches [24].…”

Applied spectroscopy in pulsed power plasmas

“…In addition to the general interest of the B-field penetration, these data are also critical to solving the energy balance in a z-pinch plasma. Combining these data with other spectroscopic measurements of the electron temperature, density, and ion velocity, Gregorian et al [19][20][21] were able to demonstrate that ϳ85% of the energy imparted to their z pinch comes from the J ϫ B force with the remainder coming from the Joule heating.…”