In the implosion experiment with high contraction ratio, the asymmetry of implosion compression and shell fuel mixing are the key factors restricting the formation of high-quality hot spot, which makes it difficult for the compression density and temperature of hot spot to reach the designed physical conditions, and there is no effective diagnostic method for spatial distribution of state parameters of hot spot. In the implosion experiment of undoped target, The parameters of hot spot electron temperature can be obtained by analyzing the bremsstrahlung spectrum. Considering that the hot spot size is only about 50μm, the research team in this paper has developed a KB microscope with four energy point quasi single energy imaging ability, which can diagnose the spatial distribution of electron temperature by multiband high-resolution imaging of hot spot bremsstrahlung. The spatial resolution of the microscope is about 5μm. Four independent imaging channels (4.51keV、6.4keV、8.04keV、9.67keV) with spectral resolution of about 10% are constructed by using a hybrid grouping design of single-layer and multilayer mirrors. Meanwhile, the team developed a simulation program for KB microscopic imaging based on Monte Carlo method. A calibration method for the spatial distribution of thermal spot imaging efficiency is developed, and an online measurement method for thermal spot drift positioning in laser device experiments is established, which solves the problem of KB microscopic imaging efficiency correction of thermal spot bremsstrahlung intensity. Before the microscope was put into experimental application, the research team used a variety of filter stack combinations on the existing four-channel spatial flat-response KB microscope to obtain the thermal spot bremsstrahlung images of three different energy bands, and directly observed the hot spot mixed region on the low-energy image. Three dimensional reconstruction of bremsstrahlung intensity of hot spot was carried out under the approximation of two-dimensional rotational symmetry of hot spot distribution, and the distribution of the electron temperature along the hot spot isoradiation line was obtained. It provides a new diagnostic method for the subsequent diagnosis of the width of the hot spot mixed zone. In the future, the research team will further expand the KB imaging energy point to close to the 20 keV energy region, and solve the problems of small imaging field of view and low imaging efficiency, so as to further improve the diagnostic accuracy of the electron temperature distribution of hot spot.

Hotspot electron temperature; Kirkpatrick-Baez microscope; bremsstrahlung imaging; hot spot mixing; multi-energy point KB microscopic imaging