An Investigation Of The Aluminum K-Edge By Spatially Resolved X-Ray Absorption Spectroscopy
X-ray absorption spectroscopy is a diagnostic technique that is able to probe the state of a plasma in detail. Such a measurement usually requires that the plasma under study not radiate in the bandwidth of the probing X-ray flux. This is usually accomplished by limiting the temperature of the sample plasma. The research presented in this thesis extends the temperature range of absorption spectroscopy so that more plasmas may be explored with this diagnostic. This is realized in the design of a novel spectrometer based around the geometry of an ellipse. The design is able to discriminate between probing X-rays and those emitted by a sample plasma, relaxing the temperature restriction. The spectrometer's unique design uses a doubly curved mica crystal for X-ray dispersion. The geometry of the spectrometer is verified by ray tracing calculations assuming Bragg reflection from mica in the second order. Control of other reflection orders is attempted by means of filtering and control of the source spectrum. This is found to be insufficient to control fifth order reflections. Potential solutions are presented to combat these fifth order reflections, but all were considered unlikely to succeed in a timely manner. The broad X-ray spectroscopy expertise gained from the development and implementation of the elliptical design is then used to explore the physics of aluminum's K-edge. This is done using point projection absorption spectroscopy to study a single 25 [MICRO SIGN]m diameter 1199 alloy aluminum wire through which a peak cur- rent of 120 kA is passed. The current heats the aluminum from room temperature to a few electronvolts. The plasma is diagnosed using a spherical quartz crystal spectrograph that records the details of the X-ray spectrum near aluminum's K-edge at 1559 eV. The spectroscopic features of the aluminum plasma are analyzed using a genetic algorithm to match observed spectra to theoretical opacity values. The quality of the fit is discussed by identifying the spectral features that are both present and missing from the opacity calculations. Comparisons are also made to past laser driven studies of the aluminum K-edge. A hypothesis to explain the missing features is proposed.
X-Ray; Absorption; K-Edge
Hysell,David Lee; Seyler,Charles Eugene
Ph.D. of Electrical Engineering
Doctor of Philosophy
dissertation or thesis