Noncollective X-Ray Thomson Scattering Diagnostic Development Based On A Titanium Hybrid X-Pinch X-Ray Source
X-ray Thomson scattering (XRTS) is the combination of elastic Raleigh scattering and inelastic Compton scattering observed from high density systems using energetic probe energies at the keV x-ray level. Thermal x-ray probes have historically been created by delivering 1014 [-] 1016 W/cm2 to a mid-Z metal foil such as titanium using kilojoule-class lasers. An XRTS probe source must provide adequate photon numbers within a finite bandwidth in order to resolve the elastic and inelastic scattering features. This thesis argues that the 4.75 keV He[alpha] spectral feature from a titanium hybrid x-pinch x-ray source driven in a pulsed power circuit can satisfy these photon and bandwidth requirements and function as an XRTS probe source. The arguments are supported through xray diode and image plate photometric analysis for the titanium He[alpha] feature. As a proof of principle, scattering signals from cold, static materials have been collected using the hybrid x-pinch as the probe source. Two different experimental scattering arrangements were developed to collect the weak scattered signals from room temperature targets. The hybrid xpinch was driven in the main current path of the Cornell Beam Research Accelerator (COBRA) 1 MA pulsed power driver for both of these arrangements. The first setup, Focused XRTS (FXRTS), used a spherically-bent germanium xray optic to focus the probe photons collected from a titanium hybrid x-pinch approximately 82 cm away, and focused them onto a 20 [MICRO SIGN]m thick aluminum foil scattering target. The FXRTS setup allowed the entire scattering experiment to be spatially removed from the actual source location, thus lowering background signals on the detectors. For the second scattering setup, Direct XRTS (DXRTS), a new spectrometer was designed and built to function inside the main COBRA vacuum chamber. The scattering setup functioned in a more traditional sense by having the scattering target, 125 [MICRO SIGN]m thick graphite, placed approximately 20 mm away from the x-pinch x-ray source. Protection of the optics and background noise shielding for the detectors were design challenges in the spectrometer. For both experimental arrangements, the backscattered radiation was collected using high-efficiency highly annealed pyrolytic graphite (HAPG) optics and focused onto Fuji Biological Analysis Systems - Tritium type (BAS-TR) image plate detectors. The noncollective FXRTS results from aluminum show the importance of the ion-ion correlation factor within the total dynamic structure factor and its strong dependence on scattering angle. The FXRTS results were fit with theoretical scattering spectrums created using an XRTS subroutine included in the SPECT3D spectral code suite. Unfortunately, the noncollective DXRTS results from graphite were mixed with line and continuum radiation from other sources that made detailed analysis impossible.
x-ray Thomson scattering; high energy density plasma; hybrid x-pinch
Seyler,Charles Eugene; Lovelace,Richard V E
Ph.D. of Electrical Engineering
Doctor of Philosophy
dissertation or thesis