| dc.description.abstract | The hollow cathode capillary discharge is of great interest as a highbrightness, short pulse soft x-ray source. This thesis presents work donein the development, modifications, and subsequent characterization of acompact plasma source comprised of a pulsed capillary discharge exploitinghollow cathode dynamics. The low inductance, low stored energy, sourceis optimized using optical, electrical, x-ray, and e-beam diagnostics. Theeffect of parameters on the capillary physics include variation of capillarylength and inner diameter, voltage, frequency, nitrogen to helium ratio inthe discharge mixture, cathode and anode aperture size and pressure. Adescription of the physical processes involved in hollow cathode initiateddischarges, with emphasis in discharge conditions leading to optimalemission in the water window with reduced emission from impurities, isundertaken. Time resolved visible spectra allowed observation of importantpre-breakdown metastable emission known to aid in discharge reproducibility.Time integrated x-ray spectra demonstrate that fast electrons producedin the hollow cathode region, of 5 ke V as determined by Faraday Cupmeasurements, are important in plasma ionization and are significant forthe x-ray emission plasma volume. Filtered diodes characterized emissionfrom the start of the current until plasma cools on being ejected fromthe anode. MCP imagery reveals good spatial stability and source size,evidencing full wall detachment. Based on comparisons between observedand simulated spectra, shorter capillaries were found to be optimal, togetherwith higher voltages, frequencies, proportion of He, local anode pressure,pressure gradient, small tube inner diameter and cathode aperture. Anaverage brightness of "'"' 140 m W per 2n srad mm2 at 28.8 Á was obtainedfor optimal geometry and discharge parameters, making this plasma apossible low-cost compact source for soft x-ray microscopy applications. | |
