Three magnetic field-plasma configurations are used to study the interaction of external magnetic fields with analytically useful, atmospheric-pressure plasmas. A magnetic field normal to the electric field in the plasma produced by the capacitive discharge vaporization of a thin Ag film is used to obtain an ExB drift motion of the plasma. Photographs show that this drift motion can drastically alter the size, shape, and location of the plasma. The same plasma-generation technique is combined with a nonuniform magnetic field to obtain an adiabatic magnetic-mirror ion trap. Finally, the cylindrically symmetric plasma produced by the capacitive discharge vaporization of a thin metal wire or a bundle of graphite fibers is combined with an axial magnetic field to obtain a theta pinch of the plasma. In all cases, the plasma current is used to generate the magnetic field in a large air-core inductor surrounding the plasma. Radiative and electrical properties of these magnetically modified plasmas will be presented.
A magnetic field of a few kilogauss oriented normal to the electric field in the plasma generated by a capacitive discharge through a thin silver film is used to obtain an ExB drift motion of the plasma. The plasma current is used to generate the magnetic field in a coil surrounding the plasma. The plasma drift motion is used to confine the plasma to the region near the surface of the plastic substrate which originally supported the thin film and the powder or solution residue sample. The result is greater interaction of the plasma with the sample, as illustrated by more rapid vaporization of the sample, reduced effects of particle size on analyte radiation intensity, and significantly improved shot-to-shot reproducibility. While analyte line intensities frequently are lower in the ExB plasma, line-to-background intensity ratios may be greater if an optical mask is used to block radiation near the substrate surface.
Time-and spatially-resolved spectroscopy is used to study the early-time spectral features of the plasmas produced by h~gh~u~ent, capacitive discharges through thin silver films. Spectra are compared for several support gases including C02, He, and an Ar/O, mixture. Al1 measurements were made during the first 40 ps of the discharge. At atmospheric pressure for all three gases, spectra from support gas species show intense lines for only a brief interval between 10 and 30 ,us after the start of the discharge. Greatest intensity from silver tines always occurs at the film surface; while greatest intensity from support gas species occurs about 2.0 mm from the film surface. A magnetic field of a few kG normal to the electric field in the plasma and parallel to the thin film surface almost completely eliminates spectral lines from the support gas species.
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