Research On Fundamental Theories And Experiments Of Double-channel Elliptically-curved Crystal Spectrograph

In the experimental investigations of inertial confinement fusion (ICF), the laser-produced high-temperature plasmas contain very abundant information, such as the electron temperature, density, ionization, etc. In order to diagnose laser-plasma distribution in space and evolution in time, it is necessary to develop the key diagnostic technology of energy, space, and time-resolved measurements. This paper was supported by the High-Technology Research and Development Program under Contract No.863-804-3, the domestic first double-channel elliptically-curved crystal spectrograph has been successfully developed, and the experiments have been carried out at the SG-2 and XG-2 laser facilities.In order to measure the laser-plasma x-ray in the short-wavelength region, the crystals are used as the dipersive elements by the x-ray diffractive principle, which cover the Bragg angles in the 5-70 degrees. The LiF, PET, Mica, and KAP crystals are utilized to measure the laser-plasma x-ray in the 0.2-2-nm region, the Bragg angles are in the range of 30-67.5 degrees.The influencing factors on transmission efficiency are studied. The reflectivity of cylindrical mirror is relative with the coated material, grazing incidence angle, and x-ray wavelength, it will increase when the x-ray wavelength increases, and it decrease faster if the wavelength is shorter. The crystal integrated reflectivity is studied by the mosaic model. The relation between the filter transmissivity and density, thickness and x-ray wavelength is studied by the Lambert-Beer law, it will decrease when the x-ray wavelength increases, and it is lower especially for the longer wavelength. The relation between the spectrographic aperture ratio and elliptical eccentricity, spectral angle is also analyzed according to the elliptical geometry, it will decrease when the x-ray wavelength increases. The transmission efficiency is calculated for KAP crystal.The angular dispersion is studied by the Bragg equation, it depends on the lattice constant and Bragg angle, it is increasing with the Bragg angle and decreasing with the lattice constant. The linear dispersion depends on the film radius, elliptical eccentricity, lattice constant and spectral angle for the x-ray film camera, it is increasing with the spectral angle and decreasing with the lattice constant. The linear dispersion depends on the distance from the exit slit to the cathode plane, elliptical eccentricity, lattice constant and spectral angle for the x-ray CCD camera, it is decreasing with the lattice constant,and firstly decreasing, then increasing with the spectral angle, the minimum is at 75 degree. The theoretical resolution is analyzed, it is mostly decided by the crystal resolving power, and it can be raised with the Bragg angle accretion. The spectral position error at the detector derives from the alignment error, it is maximum from the alignment error at the short axis.The optical path is designed by the elliptical self-focusing geometry, the crystal is elliptically curved, the source is placed at the first focus, and the exit slit is placed at the second focus. The eccentricity and focal distance are 0.9586 and 1350 mm, respectively. So the spectrograph has self-focusing characteristics and invariant optical distance. The twin elliptical crystal analyzers are intersected symmetrically in the vertical direction, the incident ray caliber is narrowed, and the spectrograph size is reduced. The designing parameters are given for the elliptical substrate, the elliptical crystal analyzers are fabricated, and two aligning schemes are designed.After the spectrograph was developed, the experiments have been executed to check the performances at the SG-2 and XG-2 high-power laser facilities.In this paper, it shows that the x-ray reflectivity is 39.2% at 2.43 nm, and blow 1% at 0.7 nm if the cylindrical mirror is coated gold and the grazing incidence angle is 3.7°, therefore, the cylindrical mirror should be cancelled in the optical path. The filter foil has very low transmissivity for the long x-ray wavelength. The...