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|Title:||Development of a Theta Pinch Discharge as a Sampling Source for Refractory Solids|
|Author(s):||White, Jeffrey Scott|
|Doctoral Committee Chair(s):||Scheeline, Alexander|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The development of a previously designed theta pinch discharge was undertaken in order to improve its ability to sample solid materials. Of primary interest were nonconducting and refractory solids.
Hardware changes in the device included the use of new power supplies, which greatly shortened capacitor charging time, and also allowed for operating the system under complete remote control through an EPROM programmed controller. Other major changes included the design of a solenoid theta coil and the use of a larger main discharge capacitor (6.05 $\mu$F).
Experiments performed included the study of differing plasma fill gases, effect of sample size and placement, effect of increasing both the inductance and capacitance of the main discharge circuit and recording the time- and space-resolved emission of the plasma species.
Results obtained are as follows: the most intense sample emission, which is taken to imply the best sampling of material, was seen for argon at 18-25 torr with the 6.05 $\mu$F discharge. Greatly increased sample emission was obtained by suspending the sample within the discharge vessel, rather than placing the sample on the vessel wall. Very marked effects were also observed depending on the width of sheet samples, with an optimum sample position 7-10 mm away from the central axis of the vessel. Increased main discharge stored energy provided increases in sample emission, as would be expected. For a given stored energy there was a clear effect depending on the risetime of the current and magnetic field waveform, with faster risetimes providing improved analyte emission. There was little effect from increased magnetic field. The time- and space-resolved plasma emission confirmed that analyte emission can be seen for long times after the ionic and continuum emission have ceased. Time discrimination will lead to increased signal-to-background values, and the elimination of possible spectral interferences.
Conclusions include: the value of the induced plasma current was the most important identified physical parameter. Higher plasma currents lead to greater plasma compression and vastly improved sampling. With the sampling of ZrC powder, it is claimed that the theta pinch discharge is capable of sampling any solid material.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
|Date Available in IDEALS:||2014-12-17|