First Investigation on the Radiation Field of the Spherical Hohlraum

The first spherical hohlraum energetics experiment is accomplished on the SGIII-prototype laser facility. In the experiment, the radiation temperature is measured by using an array of flat-response x-ray detectors (FXRDs) through a laser entrance hole at four different angles. The radiation temperature and $M$-band fraction inside the hohlraum are determined by the shock wave technique. The experimental observations indicate that the radiation temperatures measured by the FXRDs depend on the observation angles and are related to the view field. According to the experimental results, the conversion efficiency of the vacuum spherical hohlraum is in the range from 60% to 80%. Although this conversion efficiency is less than the conversion efficiency of the near vacuum hohlraum on the National Ignition Facility, it is consistent with that of the cylindrical hohlraums used on the NOVA and the SGIII-prototype at the same energy scale.

Figure 1

Schematic view of the experimental setup, the arrangement of the main diagnostic devices and the view fields of the FXRDs at the four different angles.

Figure 2

The temporal behaviors of radiation temperature measured by the FXRDs (black solid lines) and calculated by the lared code (black dashed lines) at the four different angles. (a) 20°, (b) 30°, (c) 45°, and (d) 55°. The blue solid and dashed lines in (a) are the measured and simulated $M$-band fluxes at 20°.

Figure 3

The simulated spatial distributions of the normalized electron density $n_e$ (a) and the laser deposition $W_l$ (b) inside the spherical hohlraum at different times.

Figure 4

(a) The simulated peak radiation temperatures as a function of the view angle (the red line with solid circle) compared to the measured results (the black squares). (b) The simulated $M$-band fraction at peak radiation temperature against the experimental $M$-band fraction determined by the FXRD and MXRD at 20°.

Figure 5

The radiation temperature (red solid circles) and $M$-band fraction (blue solid squares) inside the spherical hohlraum determined by the shock wave technique.

Figure 6

(a) The time-dependent sums of incident laser energy $E_{\text{laser}}$ (black line), absorbed laser energy $E_{\text{abs}}$ (red line), total converted x-ray energy $E_{\text{xtot}}$ (blue line), x-ray energy absorbed by the hohlraum wall $E_{\text{wall}}$ (green line), and the x-ray energy escaping from the LEHs $E_{\mathrm{LEH}}$ (cyan line). (b) The nominal conversion efficiencies of the spherical hohlraum for the different experimental shots obtained by using the observed radiation temperatures of the FXRDs. The black circles, red diamonds, blue stars, and green squares are the nominal conversion efficiencies calculated by using the radiation temperatures measured by the FXRDs at 20°, 30°, 45°, and 55°, respectively.