Electron density measurements behind a hypersonic shock wave in argon

Abstract

The purpose of the research is to characterize the ionization process behind a shock wave with precursor photoionization in argon. In this study, the H- line is observed by spectroscopic measurements using a hypersonic shock tube and the Stark broadening of the H- line is evaluated to obtain the electron density behind a shock wave. As a result, the electron density is on the order of 10 21 m -3 and tends to decrease with increasing the distance from the shock front. The decrease of the measured electron density is caused by the radiative energy loss from the test gas because the radiative energy loss corresponds to a decrease of the temperature or the density of the test gas, both of which can decrease the electron density. Previous study showed that photoionization occurred ahead of the shock wave, making use of the radiation energy emitted from the region behind the shock wave. The fact might be related to the radiative energy loss obtained in the present study. From the present study, it is found that the radiative energy loss is dominant behind the shock wave under the condition that precursor photoionization occurs ahead of the shock wave. In future, we should investigate the radiative transfer phenomena around the shock wave for further clarification.

Optical Diagnostics of Shock-induced Argon Plasmas Based on a Simple Collisional-Radiative Model

“…The detail of CFD calculation is described in a previous study. [9] The electron temperature obtained using the CR model qualitatively agrees well with the calculated one. However, these values are slightly scattered due to the deviation of the peak intensities in the measured spectra.…”

“…Our past study shows that the electron density of argon plasma induced by a hypersonic shock tube is on the order of 10 21 m -3 . 9) In addition, the effective principal quantum number for most energy levels is higher than Byron's boundary. Therefore, ladder-like electron impact transition is considered to be important for argon atoms in this condition.…”

“…, σ π (9) where me is the mass of the electron. ui,j is the dimensionless energy expressed as ui,j = εi,j / (kBTe) using the electron energy εi,j .…”

“…8) In addition, spectroscopic measurements showed that the electron density behind the shock wave tended to drop due to the radiative energy loss from the test gas. 9) The energy loss is considered to be the energy source of the photoionization. These results pointed out that the thermochemical state around the shock wave was out of equilibrium.…”

Influence of atomic kinetics in the simulation of plasma microscopic properties and thermal instabilities for radiative bow shock experiments

“…The first one is the analysis of the validity of LTE assumption in the calculation of average microscopic properties of argon plasmas in mass densities and electron temperatures ranging from 10 −6 to 10 −1 g cm −3 and from 1 to 100 eV, respectively. Argon is an element commonly used in laboratory astrophysics experiments on radiative shocks generated using either pulsed power devices [19,[21][22][23][24] or ultraintense lasers [17,[25][26][27][28][29][30], and the ranges of plasma conditions of these experiments fall within the ones before mentioned, hence, the interest of this study. For this analysis, we have made calculations assuming the plasma either in LTE and therefore using the Saha-Boltzmann (SB) equations, or in non-LTE (NLTE) in steady state, in which we have solved the rate equations implemented in our collisional-radiative model.…”