Spectroscopic Determinations Of Magnetic Fields, Electron Temperatures, And Electron Densities In Single Wire Aluminum Plasmas

摘要

This dissertation provides a detailed determination of the visible emission spectra and plasma parameters of an exploding single aluminum (Al) wire while addressing the applicability of a new spectroscopic measurement technique to measure magnetic fields (B) in dense plasmas, where magnetic field measurements were previously unobtainable. Through the use of this new technique, hereafter called "Zeeman Broadening", there was evidence for magnetic fields in the spectra and a measurement was made. The Zeeman Broadening technique was first proposed and employed at the Weizmann Institute of Science in Rehovot, Israel [47] and is based on the difference in line-widths of two fine structure components of the same multiplet that undergo different splittings due the magnetic field. Experiments were conducted exploding fine Al wire using Cornell's Low Current Pulser 3 (LCP3), a pulsed power generator that initially produced a 10 kiloamp (kA) current pulse with a rise time of 500 nanoseconds [16]. It was later modified to produce up to 13kA with a 450ns rise time. Aluminum 1100 alloy wires were used, which are 99.9% Al. The wire length was 1.0cm, and the diameter ranged between 15[MICRO SIGN]m and 33[MICRO SIGN]m. The primary diagnostics included a high resolution grating spectrometer coupled to either a Kentech gated optical imager (GOI), Princeton Instruments PIMax3 gated intensified charge-coupled device (ICCD), or an Andor iStar ICCD. Additional diagnostics included pulser current, wire current, and load voltage monitors. The first set of experiments, with the GOI, were exploratory and meant to determine an initial electron temperature and electron density. Using these data it was concluded that the plasma parameters were conducive to the Zeeman Broadening technique, and the PIMax3 camera was borrowed from Princeton Instruments to create a diagnostic setup with resolution sufficient for studying the magnetic field. While the spectra were unsatisfactorily noisy, a magnetic field of B = 3.5T was fitted to a spectrum at a radius of 500[MICRO SIGN]m from the initial wire position at peak current. This result implies a high portion of the 10kA current remained within r [LESS-THAN OR EQUAL TO] 500[MICRO SIGN]m, even though the plasma had expanded beyond a 2mm radius. To gather more data with improved signal-to-noise ratios, a Shamrock 500i spectrometer and iStar camera were borrowed from Andor Technology. The spectra were analyzed to determine electron density ne and electron temperature T e over many radii throughout the evolution of single wire explosion. Over the entire single wire explosion, the ne ranged between 8 x 1016 cm[-]3 and 1.6 x 1018 cm[-]3 , while the T e was measured between 2eV and 4eV . The exploding wire plasma formed a hot less dense plasma shell surrounding a colder and denser core, both expanding outwards at a rate of ~ 3km/ s. In the Andor data set there also existed indications of measurable magnetic field that implied significant portions of current was flowing within r [LESS-THAN OR EQUAL TO] 500[MICRO SIGN]m, in agreement with the previous results.