Iron-Plasma Transmission Measurements at Temperatures Above 150 eV

Measurements of iron-plasma transmission at $156\pm 6\mathrm{eV}$ electron temperature and $6.9\pm 1.7\times {10}^{21}{\mathrm{cm}}^{-3}$ electron density are reported over the 800–1800 eV photon energy range. The temperature is more than twice that in prior experiments, permitting the first direct experimental tests of absorption features critical for understanding solar interior radiation transport. Detailed line-by-line opacity models are in excellent agreement with the data.

Figure 1

Iron opacity calculated at the radiation-convection boundary in the sun (red) and at the conditions in $Z$ experiments (green). The Planck function derivative with respect to temperature evaluated at 182 eV (black) illustrates the photon energies most important for the solar radiation transport.

Figure 2

Schematic experiment diagram. Space-resolved spectra from one of the thick sample experiments are shown above the diagrams.

Figure 3

Average experimental transmission from the thick samples (black line, $h\nu >990\mathrm{eV}$) and the thin samples (black line, $h\nu <990\mathrm{eV}$). The spectral range including the Fe $b\mathrm{\text{−}}f$ and Mg $K$ shell (a) is compared with PrismSPECT (red) and OPAL (green). Comparisons in the Fe $L$ shell spectral energy range are shown for PrismSPECT (b), OPAL (c), and MUTA (d) (models in red). The charge states and configurations responsible for many of the strong absorption features are indicated, although millions of $b\mathrm{\text{−}}b$ transitions are present.

Figure 4

Thick sample experiment mean transmission (red) compared with the thin sample experiment scaled mean transmission ($T_{\mathrm{scaled}}=T_{\mathrm{thin}}{}^{1.9}$, blue).