The Low Density Plasma Sheath in Cylindrical Geometry

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Ion laser plasmas

The typical noble gas ion laser plasma consists of a high-current-density glow discharge in a noble gas, in the presence of a magnetic field. Typical CW plasma conditions are current densities of 100 to 2000 A/cm^2, tube diameters of 1 to 10 mm, filling pressures of 0.1 to 1.0 torr, and an axial magnetic field of the order of 1000 G. Under these conditions the typical fractional ionization is about 2 percent and the electron temperature between 2 and 4 eV. Pulsed ion lasers typically use higher current densities and lower operating pressures. This paper discusses the properties of ion laser plasmas, in terms of both their external discharge parameters and their internal ion and excited state densities. The effect these properties have on laser operation is explained. Many interesting plasma effects, which are important in ion lasers, are given attention. Among these are discharge nonuniformity near tube constrictions, extremely high ion radial drift velocities, wall losses intermediate between ambipolar diffusion and free fall, gas pumping effects, and radiation trapping. The current status of ion laser technology is briefly reviewed

Resonance Oscillations in a Hot Non-Uniform Plasma

The hydrodynamic equations of a hot non-uniform plasma are solved numerically in slab geometry to obtain the resonant frequencies and associated wave functions. The splitting of the various resonances is shown to depend on the parameter: (slab thickness + Debye length)

Resonance Oscillations in a Hot Non-Uniform Plasma

The hydrodynamic equations of a hot non-uniform plasma are solved numerically in slab geometry to obtain the resonant frequencies and associated wave functions. The splitting of the various resonances is shown to depend on the parameter: (slab thickness + Debye length)

Measurement of the current and symmetry of the impact liner on the NTLX experiments

A series of four liner implosion experiments, denoted the Near Tern Liner Experiments (NTLX) was recently conducted on the Shiva Star capacitor bank at the Air Force Research Laboratory (AFRL). Measurement of the driving currents in these experiments is required for postshot analysis of the liner implosion and experiments conducted in the target cylinder. A Faraday rotation measurement was fielded on Shiva Star to measure the current and compare with the current measured by a Rogowski coil technique. The Faraday rotation technique measured the 16 MA currents in these experiments with better than 1% precision. In addition, six B-dot probes were fielded at equal angles around a circle in the powerflow channel outside the liner to measure the symmetry of the liner impact on the target cylinder. The B-dot probes measure the local Idot, which has a jump when the liner impacts the target cylinder. A high-pass filter allows one to measure this jump more accurately. From the relative timing of the jump signals, the offset of the liner axis and the circularity of liner are inferred

Solid Dielectric Transmission Lines for Pulsed Power

This paper documents recent work developing solid dielectric transmission lines for sub-microsecond, 100 kV class compact pulsed power systems. Polymer-ceramic nanocomposite materials have demonstrated sub-microsecond discharge capability in parallel plate capacitors and transmission lines [1, 2]. With a dielectric constant of approximately 50, the propagation velocity is 2.5 cm/ns, necessitating lines of several meters length to achieve \u3e 100 ns pulse lengths. By folding the line in a fashion analogous to ceramic multilayer capacitors, the physical length of the line can be significantly shorter than the electrical length. We present the results of an experimental effort to develop a folded transmission line using a polymer-ceramic nanocomposite dielectric. The pulse length was somewhat shorter than expected based on a simple calculation using the geometry and the dielectric constant. Fully 3-D electromagnetic calculations were used to examine the role of the edges in curtailing the pulse length. Dielectric breakdown in this device occurred below the electric field threshold demonstrated in the prior work [1]. Improvements in the large scale fabrication of TiO2 beginning with nanoscale grains have opened the possibility for producing single layer high voltage devices. Given a dielectric constant approaching 140, transmission lines using nano-TiO2 can be considerably shorter than with other materials. Relatively thick, flat sheets of TiO2 have been fabricated for testing up to 50 kV. Several transmission lines, employing a serpentine electrode geometry, have been manufactured and tested. Testing up to several 10\u27s of kV has confirmed the operation of the lines according to the design. As expected, the triple point between the TiO2, electrode, and insulating medium has proven difficult to manage for high voltage operation. Several techniques to mitigate the effects of the triple point, including resistive grading at the edges of the electrodes, are discussed. Fully 3-D electromagnetic modeling is used to examine the effects of electrode geometry and composition on the performance of the lines

Material science experiments on the Atlas Facility

Three material properties experiments that are to be performed on the Atlas pulsed power facility are described; friction at sliding metal interfaces, spallation and damage in convergent geomety, and plastic flow at high strain and high strain rate. Construction of this facility has been completed and experiments in high energy density hydrodynamics and material dynamics will begin in 2001