Early hot electron can preheat the pellet fuel and thus lead to lower implosion performance. To evaluate the influence of early hot electrons on implosion, the properties of hot electrons in early stage of implosion experiments in Shenguang-100kJ laser facility were investigated. It was shown that both the temperature and energy of early hot electrons were very low. The upper limit of the temperature and energy of early hot electrons in our experiments were only 7.7keV and 0.35J, respectively. Besides, the generation mechanisms of early hot electrons were also different from NIF experiments according to the results of the hard x-ray imager (HXI). In NIF experiments, two-plasmon decay and multi-beam stimulated Raman scattering (SRS) were dominate mechanisms that generate early hot electrons, however, SRS of the outer beams were our dominate mechanism because of the higher intensity of the outer beams. As a supplement to the experiment, spectrum of the scattered light of SRS was obtained by radiative hydrodynamic and ray tracing simulations, the result showed that the spectrum of the scattered light was peaked at λ_s=482nm. According to theories of laser-plasma instability, hot electrons with the temperature near 7keV can be generated. Furthermore, energy of hot electrons deposited onto the pellet was estimated to less than 6.8×10^-3J from the result of HXI. Deeper analysis showed that, in the beam overlapping region, the plasma density was unsuitable for multi-beam SRS, so no hot electrons with larger temperature were generated.

Hot electrons, laser plasma instability,,Inertial confinement fusion; High power laser; diagnostics technique