Numerical Study On High Spatial Resolution Diagnostics Of Plasma By X-ray Imaging Of A Zone Plate And Scattering In Electron Radiography

To diagnose interfaces, density profile of ablative front and hydrodynamic instability in inertial confinement fusion (ICF),1μm spatial resolution is required in experiments. In this dissertation, X-ray Fresnel phase zone plate (FPZP) imaging and electron radiography are numerically studied to assure the spatial resolution property in plasma diagnosticss:1. The spatial resolution, depth of focus, efficiency of energy and translational invariance of Fresnel phase zone plate (FPZP) illuminated by a point X-ray source are obtained from a domestically coded MATLAB program. Based on the translational invariance, imaging of an extended X-ray source is simulated under a typical experimental condition of image-to-source magnification of 10 when using an FPZP with its outmost zone width of 0.35μm. Results show that the image contrast decreases with the increase of the source size, and the zeroth-order and the minus first-order diffractions of the FPZP contribute mainly to the image background enhancement and the contrast decrease. The spatial resolution to the objective plane is also reduced. For a 1-mm-square-shape source with a sinusoidal-distribution intensity modulation of contrast 1, the image modulation contrast is below 0.4, and the spatial resolution is 0.75 μm.2. Simulation to the Gabor zone plate (GZP) illuminated by a point X-ray source gives out the diffractive property of single order, resolution and field of view. The resolution and field of view is close to a corresponding FPZP. A novel single-focus x-ray zone plate is proposed by stagger arrangement of zones, which would be technically easy to manufacture. Theoretical design shows that the transmission function of the plate is a cosine function of radius, like that of a GZP. Numerical simulation at the wavelength of 0.275 nm shows the single-order focusing property of the plate. Its spatial resolution is also the same to a corresponding conventional FPZP. The first-order diffraction efficiency of 11.5% is higher than a conventional GZP results from the phase-shift of the material of the plate.3. Single Monte Carlo method is used to simulate the transport of electron beam in plasma. When radiographing a micrometer scale transition layer with gradient density between two plasma layers, the existence of the transition layer can be assured from the scattered pattern, but the exact width cannot be resolved. When radiographing a 10 μm wavelength sinusoidal perturbed target with two-density or two-material layer, scattered pattern can clearly reflect the interface. As the scattered pattern results from electron scattering between interfaces, the contrast depends on the position of the detector. The contrast can achieve more than 0.3 when setting the detector at a suitable position and keeps a high level of more than 0.2 in the range of tens of micrometers. For smaller perturbation wavelength target, the detector should be more accurated posited.