108 / 2023-04-13 21:50:00

Recent experimental progresses on energetics of octahedral spherical hohlraum

As a promising hohlraum for indirect-drive inertial confinement fusion, octahedral spherical hohlraum has the following advantages: the natural and robust high radiation symmetry, high energy coupling efficiency and low risk of laser plasma instability. To achieve a better design of this hohlraum, we need to know what kind of the laser entrance hole (LEH) is better, as well as the optimal size of the LEH. We should also know how the laser spots move on the hohlraum wall, so that we can judge whether the laser energy will be lost from other LEH or dissipated in the gold bubble generated by other beams. In recent years, we performed several experiments on SG hundreds-kJ facility to answer the above questions. We researched laser injection into the LEHs with different sizes. The results showed that for a laser beam with a 1000μm diameter, the optimal LEH size (1000μm) is 1800μm. This size ensured that near all laser energy is injected into hohlraum and the least X-ray energy is lost from the LEH. Five sets of data (from a x-ray framing camera, two x-ray pinhole cameras, five flat-spectral-response X-ray diodes and five M-band X-ray diode) self-consistently proved this conclusion. We also researched the spots motion of the laser in the octahedral spherical hohlraum. The result showed that the laser energy would neither be lost from other LEHs, not be dissipated by the bubble generated by other beams, which further proved that octahedral spherical hohlraum was a practical and robust hohlraum for indirect-drive inertial confinement fusion. In addition, we proved that uranium was a better hohlraum wall material than gold. Several energetic properties including soft x-ray radiation and hard x-ray radiation, et al. were better in uranium hohlraums. These experiments help us to achieve a better design for this hohlraum.