Influence of a LIGA-raster on the spatial distribution of the radiation from a flash X-ray generator
The development of essentially new methods of manufacturing of X-ray optics in the energy range 20-200 keV is a challenge. Namely, the development of manufacturing methods of X-ray rasters with high aspect ratio and, on substrates of any forms, using LIGA technique. A spherical X-ray wave can be formed, placing a foil with microchannels onto a spherical surface either near the X-ray focus or away from the focus. In case of a plane raster, the quasi-plane wave with a divergence determined by the ratio of the diameter to the lengths of channels will be formed. At the same time, for X-ray tubes of all the types, including flash generators applied at the Institute of Hydrodynamics SB RAS for the diagnostic of high-speed and explosive processes, a three-dimensional microraster can be used as a collimator. That allows a decreasing of the visible source size, resulting in an increasing of the spatial coherence of the X-ray beam. In the experiment, a flat nickel raster of 1250 microns thick, whose channels are 80 microns in diameter, and manufactured using LIGA technique, has been applied. For a flash X-ray device with an explosive electron emission and a bias of 150 kV, the angular divergence was reduced from 180 degrees to 3 degrees (FWHM), i.e. 60 times. The quasi-parallel X-ray beam along the axis passing from the center of the focus and perpendicular to the raster was formed. The beam diameter is similar to the focus size in the near field and divergent (with an angular divergence of 3 degrees) in the far field. Because of non-zero raster transparency, a background of scattered radiation has been observed. The intensity of the background is characterized by the sixth order of symmetry that corresponds to the raster symmetry. Thus, the opportunity of the use of microraster manufactured by means of LIGA for the increase of spatial coherence of X-rays is experimentally demonstrated.