Research On The Technology Of Plasma X-ray Imaging Based On Logarithmic Spiral Bent Crystal

The researches on Inertial Confinement Fusion(ICF) and Z-Pinch showed important research and application value not only in basic physical exploration, but also in the field of national economy and military affairs. To be settled in the physical complexity and controllability of ICF and Z-pinch, it is necessary to establish a comprehensive diagnosis system which is the important part of the process in ICF and Z-pinch researches.In ICF and Z-Pinch researches, bent crystal imaging spectrometers are the routine equipment for the X-ray plasmas imaging. The key component of these imaging spectrometers is a bent Bragg crystal in general. However, one configuration using spherically bent crystals always suffers from a small field of view, encountering the geometric constraints. Another configuration is to use toroidally bent crystals. However, it is much more complex to fabricate a high-quality toroidal surface, and it is difficult to align the imaging optics due to constraints on all six degree freedom of positioning. In addition, for imaging spectrometers using the reflection crystals(Bragg crystals) mentioned above, the effective area is usually restricted by the rocking curve width of the crystals. Compared with the reflection-type crystal analyzer, the transmission-type Laue crystal can be inserted and aligned from a single direction to avoid the geometric constraints, and when the Laue crystal is bent into the logarithmic spiral shape, the crystal will present the same angle of incidence to the beam emanating from a point source. Owning to these merits, the Bragg condition will be fulfilled over a large angle. In the existing literature, much research has been performed using logarithmically bent Laue crystals in the spectroscopy to resolve X-ray fluorescence and phase contrast imaging for biological and medical imaging, and in the spectrometry to characterize the hard X-ray spectrum of a laser-induced plasma X-ray source. However, little has been investigated in the monochromatic backlight imaging of plasmas using logarithmically bent Laue crystals.Due to the urgent demand for plasma monochromatic x-ray imaging diagnosis in e ICF and Z-pinch shrinkage implosion process, supported by the National Natural Science Foundation(No.10976033) "Research on high-temperature plasma X-ray spherical crystal monochromatic imaging spectrum" and China Academy of Engineering Physics Sciences and Technology development fund project(No.2010B0401050) "Research on logarithmic spiral curved crystal in the Z-pinch shrinkage in plasma diagnostics", around the logarithmic spiral curved crystal imager X-ray monochromatic imaging principle and application, we carry out the research work as follows,(1) The geometric properties of the logarithmic spiral have been analyzed. According to its characteristics, analyze the effects of the logarithmic spiral geometry parameters on its properties. Combining the mechanism of X-ray diffraction in crystals, analyze the X-ray diffraction characteristics of the logarithmic spiral crystal. These analysis results will provide theoretical basis for the development of logarithmic spiral shaped bent crystal.(2) According to the X-ray monochromatic diffraction principle and the slice layer model of the bent crystal, the characteristics of the plasma X-ray monochromatic diffraction by the logarithmic spiral curved crystal were investigated. Based on the analys is mentioned above, the logarithmic spiral Laue bent crystal formula in the transmission type was derived, and the monochromatic x-ray imaging principle of transmission type was studied; The performance parameters including imaging amplification ratio, field imaging, spatial resolution were theoretically analyzed. The position selection principle of imaging detector was investigated, and the ray tracing theory was applied to simulate the transmission type logarithmic spiral imaging system to show the influence of backlight position offset on imaging performance.(3) We have developed the transmission logarithmic spiral of Laue bent crystal imager with the lattice constant of 0.8512 nm, and established the monochromatic backlight imaging experimental platform to carry out the transmission type logarithmic spiral bent crystal analyzer on plasma X-ray monochromatic backlight imaging test; Cu Target X-ray source was selected as the background light source, with the characteristic spectral wavelength of 0.154 nm.The monochromatic X-ray backlighting experiments were conducted using various sizes of micro grid(grid diameter varies from 50 μm to 200 μm),which verified large field of view when imaging by the transmission type logarithmic spiral of Laue bent crystal analyzer. The FWHM of the diffractive image(edge extension of the mesh peak ranges from 12.5% to 87.5%) showed that, when the size of the background light was 110 μm, the spatial resolution of the imager in the meridian and sagittal direction was 30 μm and 37 μm, respectively.(4) The pinhole with reflective logarithmic spiral crystal monochromatic imager was developed. Aimed at Al wire array implosion plasma, we conducted the Z-pinch shrinkage in explosion plasma K-shell monochromatic imaging experiments on Yang accelerator at the China Academy of Engineering Physics, by using quartz(1010) and mica(002) logarithmic spiral crystal analyzer aimed at hydrogen-like line Al Lyα2(2p1/2 –1s1/2) and helium-like line Al Heα(1s2p 3P1 –1s2 1S0), and eventually obtained the wire array plasma spectrum corresponding monochromatic image. The results showed that the spectrograph can reflect the exploding modality of Z-pinch Al plasma, and multi-hotspots due to magnetic Rayleigh-Taylor instability also appeared on the images. The helical structure reflected by the helium-like line monochromatic image also showed that axial magnetic field frosting the expanding plasma was appeared in the process of pinch.(5) Based on the development of single channel logarithmic spiral crystal imager, multi-channel logarithmic spiral crystal imager is proposed in order to improve the imaging efficiency, and concurrently capture the wire array implosion plasmas corresponding to multiple energy spectrum of monochromatic at the same time. The corresponding experiments for Z-pinch shrinkage of aluminum wire array implosion plasma monochromatic imaging are also executed on the Yang accelerator. In the successfully captured Al wire array multi energy point monochromatic image, differences of the spatial intensity distribution between the images of different energy points. The clear zone of Hα line is narrower than that of Heα line, and more focused on the axis of the wire array plasma, which shows that the number of the atoms excited to the hydrogen-like plasma is smaller than that excited to the helium-like plasma. The bright spot centers are concentrated on the axis, which reveals that the plasma temperature and density in the center of axis are higher than that in the periphery of axis, in accordance with the implosion rule of the practical Z pinch. What’s more, in the multiple energy point monochromatic images captured by the Imager, the forms of the images corresponding to Al Heα line(1.5894 keV) and its mutual combination line(1.5883 keV), as well as Hα line(1.729 keV) and its mutual combination line(1.7277 keV) are totally different, which reveals that multichannel imager is capable of distinguish these energy points, and its energy resolution is less than 1.3 eV.