Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Michael Purvis
M.S. Final
Feb 29, 2008, 1:30pm
Forestry 107
Plasma interactions in laser-irradiated cavities studied with soft x-ray interferometry
Abstract: This thesis presents the study of dense laser-created colliding plasmas using soft x-ray laser interferometry a technique capable of extending the domain of interferometric diagnostics of plasmas to higher electron densities and larger scale lengths. Series of two-dimensional electron density maps were measured using a 46.9 nm wavelength tabletop capillary discharge soft x-ray laser probe in combination with an amplitude division interferometer based on diffraction gratings. The dense colliding plasmas were created focusing a Ti:Sapphire laser delivering 120 ps pulses onto the surface of semi-cylindrical and v-shaped groove targets at intensities of ~1012 W cm-2. The experimental results are compared and interpreted with two-dimensional simulations performed using the radiation hydrodynamics code HYDRA. In the case of the semi-cylindrical cavities, measurements obtained for aluminum and carbon targets describe the radial expansion of plasma towards the axis of the cavity where it converges forming a concentrated localized high density plasma region with densities exceeding 1×1020 cm-3. Comparison of the electron density profiles with simulations, show that the abrupt density increase near the axis is dominantly caused by the convergence of plasma generated at the bottom of the groove during laser irradiation. In the case of the triangular cavities, measurements show the formation of a thin plasma jet that expands along the symmetry plane at Mach 3-5 and that later evolves into a broader plasma plume with significant side lobes. Two-dimensional simulations reveal that the jet is formed by accelerated material ablated from the vertex and by the continued sequential arrival of wall material along the symmetry plane, where it collides and is re-directed outward. Simulations revealed that radiative cooling contributes to maintaining the jet’s collimation. The results from both studies illustrate that the combination of soft x-ray laser interferometry with 2-dimensional hydrodynamic simulations is a powerful tool to for studying the dynamics of dense plasmas.
Adviser: Jorge Rocca
Co-Adviser: Not applicable
Non-ECE Member: Chiaoyao She
Member 3: Carmen Menoni
Addional Members: Not applicable
Program of Study: