X-ray heating and electron temperature of laboratory photoionized plasmas

We discuss the experimental and modeling results for the x-ray heating and temperature of laboratory photoionized plasmas. A method is used to extract the electron temperature based on the analysis of transmission spectroscopy data that is independent of atomic kinetics modeling. The results emphasized the critical role of x-ray heating and radiation cooling in determining the energy balance of the plasma. They also demonstrated the dramatic impact of photoexcitation on excited-state populations, line emissivity, and radiation cooling. Modeling calculations performed with astrophysical codes significantly overestimated the measured temperature.

Figure 1

Spectrally resolved x-ray flux impinging on the gas cell at the peak of the drive (red), and breakdown in three scaled Planckians of $T_R=153$ eV (blue), $T_R=76$ eV (brown), and $T_R=45$ eV (green).

Figure 2

Transmission data from Z shot z2222 ($P=30$ Torr) showing $K$-shell line absorption in Be-, Li-, He-, and H-like neon ions. The labels indicate the neon ion and the upper (final) principal quantum number of the absorption transitions.

Figure 3

Time histories of radiation heating $R_H$ ($•$), cooling $R_C$ ($+$), and net heating $R_N=R_H-R_C$ (thick lines) rates from the helios-cr simulation of the neon gas cell experiment for $P=30$ Torr. Results are shown including full (blue) and scaled-down (red) photoexcitation rates. The peak of the x-ray drive is at $t=100$ ns.

Figure 4

Electron temperature measurements and time histories from helios-cr simulations of neon gas cell experiments (red lines) for (a) $P=7.5$, (b) 15, and (c) 30 Torr, and from Boltzmann kinetics (blue lines with dots) for $P=7.5$ and 15 Torr. The measurement and helios-cr simulation of the SiO-tamped foil experiment are also shown (d). The peak of the x-ray drive is at $t=100\pm 0.5$ ns.

Figure 5

Time histories of radiation heating $R_H$ ($•$), cooling $R_C$ ($+$), and net heating $R_N=R_H-R_C$ (thick lines) rates from the helios-cr simulation of the SiO expanding foil experiment. Results are shown including full (blue) and scaled-down (red) photoexcitation rates. The peak of the x-ray drive is at $t=100$ ns.