Nonlinear transmission line-driven apparatus for short-pulse microwave exposure of aerosolized pathogens.

A system capable of exposing a flowing aerosol stream to short duration (2-4 ns), high-power RF waveforms is described. The system utilizes a C-band gyromagnetic nonlinear transmission line source having peak power outputs ranging as high as 80 kW at a center frequency of 4.2 GHz.

Brazed carbon fiber fabric field emission cathode.

Field emission cathodes, comprised of commercially available carbon fiber fabrics directly brazed to metal substrates, were fabricated and tested. Cathodes fabricated in this manner eliminate the need for an epoxy bond between the carbon fibers and the substrates and can be baked, in a vacuum, at high temperatures, limited by the re-melt temperature of the braze. Preliminary testing at mildly relativistic voltages (200 kV-300 kV) yielded average current emission densities of 100's of A/cm, which are in line with previously published results on epoxy-bonded carbon fiber field emission cathodes.

Apparatus for generating quasi-free-space microwave-driven plasmas.

An apparatus for generating quasi-free-space microwave-driven plasmas has been designed, constructed, and tested. The plasma is driven by a multi-kW, ∼5 GHz microwave beam focused at the center of a vacuum chamber using a Koch-type metal plate lens. Sustained plasma discharges have been generated in argon at pressures ranging from 150 to 200 mTorr, at beam power levels ranging from 5 to 10 kW, and at gas flow rates of approximately 200 SCCM.

Pressure and energy balance of stagnating plasmas in z-pinch experiments: implications to current flow at stagnation.

Detailed spectroscopic diagnostics of the stagnating plasma in two disparate z pinches allow, for the first time, the examination of the plasma properties within a 1D shock wave picture, demonstrating a good agreement with this picture. The conclusion is that for a wide range of imploding-plasma masses and current amplitudes, in experiments optimizing non-Planckian hard radiation yields, contrary to previous descriptions the stagnating plasma pressure is balanced by the implosion pressure, and the radiation energy is provided by the imploding-plasma kinetic energy, rather than by the magnetic-field pressure and magnetic-field-energy dissipation, respectively.

Measurement of temperature, density, and particle transport with localized dopants in wire-array Z pinches.

Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.