Hohlraum plasma motion is a critical problem in inertial confinement fusion research. The mixing of gas-wall interface is one of the possible reasons for the so-called “drive deficit”. Literatures have pointed out that Rayleigh-Taylor instability and Kelvin-Helmholtz instability may grow at this interface, thus leading to mixing. However, observation of such instability at this low density region has yet been reported. Thomson scattering has the potential to realize the above observation due to its high sensitivity to underdense plasma conditions. We have carried out experiments with simple cylindrical hohlraums at different gas-fill density and laser irradiance, using Thomson scattering to measure the motion and mixing of gas-wall interface. The autoluminescence of hohlraum coronal plasma expansion is measured by an X-ray framing camera, and the 5f-3d emission spectra of gold plasma are measured by a gated crystal spectrometer. The plasma flow velocity, ionization state, electron temperature and density evolution are obtained by joint diagnosis. The experimental results show that there is a significant shear flow at the gas-wall interface, which meets the conditions to form Kelvin-Helmholtz instability. When the disturbance is enhanced, the Thomson scattering spectrum has periodic oscillation of frequency. One of the possible reasons is the periodic disturbance of flow velocity, and the other is the periodic change of density on the optical path. By comparing the laser injection conditions, it is confirmed that the overlapping effect of laser beams is an important factor affecting the interfacial disturbance in this coronal region.

Thomson scattering,mixing,hohlraum