F. J. Wessel

Propagation of neutralized plasma beams

Beams of charge- and current-neutralized plasma will cross a transverse-magnetic field by a combination of collective-plasma processes. These processes were studied for a high -to-low beta (β ≡ plasma energy density/magnetic field energy density) hydrogen-plasma beam injected into a vacuum transverse magnetic field with nominal parameters: T_i ≈ 1 eV, T_e ≈ 5 eV, n ≤ 10¹⁴ cm^-3, v_i ≤ 9 × 10⁶ cm/s, t_pulse <; 60; 70 μs, B_z ≤ 300 G. Plasma characteristics were measured for a wide beam, a/ρ_i ≤ 35, and a downstream distance, x ≤ 300 ρ_i, where a is the beam radius, x is the downstream distance, and ρ_i is the ion gyroradius. A brief state of initial diamagnetic propagation is observed, followed by a rapid transition to E×B propagation. E×B propagation is accompanied by beam compression transverse to B. with as much as a factor of four increase in density and a slight drift of the beam in the ion Lorentz force direction. As the magnetic field increases, the observed magnetization time decreases from that calculated using classical Spitzer conductivity, approaching an order of magnitude. This rapid magnetization can be accounted for using classical Hall conductivity, rather than invoking anomalous processes or instabilities to calculate the magnetization time.

Plasmoid propagation in a transverse magnetic field and in a magnetized plasma

The propagation of plasmoids (neutralized ion beams) in a vacuum transverse‐magnetic field has been studied in the University of California, Irvine laboratory for several years [Phys. Fluids 24, 739 (1981); 25, 730, 2353 (1982); 26, 2276 (1983); J. Appl. Phys. 64, 73 (1988)]. These experiments have confirmed that the plasmoid propagates by the E×B drift in a low beta and high beta plasmoid beam (0.01<β<300), where β is the ratio of beam kinetic energy to magnetic field energy. The polarization electric field E arises from the opposite deflection of the plasmoid ions and electrons, because of the Lorentz force, and allows the plasmoid to propagate undeflected at essentially the initial plasmoid velocity. In these experiments, plasmoids (150 keV, 5 kA, 50–100 A/cm2, 1 μ sec) were injected into transverse fields of Bt=0–400 G. Anomalously fast penetration of the transverse magnetic field has been observed as in the ‘‘Porcupine’’ experiments [J. Geophys. Res. 91, 10,183 (1987)]. The most recent experiments ar...

Ultrahigh magnetic fields produced in a gas .. puff Z pinch

Controlled, ultrahigh axial magnetic fields have been produced and measured in a gas‐puff Z pinch. A 0.5‐MA, 2‐cm‐radius annular gas‐puff Z pinch with a 3‐min repetition rate was imploded radially onto an axial seed field, causing the field to compress. Axial magnetic field compressions up to 180 and peak magnetic fields up to 1.6 MG were measured. Faraday rotation of an Argon laser (5154 A) in a quartz fiber on‐axis was the principal magnetic field diagnostic. Other diagnostics included a nitrogen laser interferometer, x‐ray diodes, and magnetic field probes. The magnetic field compression results are consistent with simple snowplow and self‐similar analytic models, which are presented here. Even small axial fields help stabilize the pinches, some of which exhibit several stable radial bounces during a current pulse. The method of compressing axial fields in a gas‐puff Z pinch is extrapolable to the order of 100 MG. Scaling laws are presented. Potential applications of ultrahigh axial fields in Z pinches...

Polarization of an intense space‐charge‐neutral ion beam incident upon a magnetic field

The collective behavior of an intense, pulsed, space‐charge‐neutral proton beam (100 kV, 3 A/cm2, 0.8 msec) incident upon a transversely oriented magnetic field of 0–6 kG has been determined experimentally. At 6 kG, a floating potential probe shows longitudinal polarization creating a positive sheath (virtual anode) within the field boundary having a peak electrostatic potential equal to the ion accelerating potential. The sheath thickness is approximately v/wpi, where v is the beam velocity and wpi is the ion plasma frequency. Oscillations in the sheath potential at wpi were observed as predicted by previous computer simulations. Ions were observed to be accelerated out of the sheath in all directions. Transverse polarization of the beam as predicted by Schmidt’s polarization drift model was not observed although the plasma dielectric constant was approximately 102.

Pulsed power for advanced waste water remediation

We describe a 2-stage technology for degrading water borne chlorinated/aromatic organic pollutants, based on a pulsed power treatment in the first stage followed by bio-treatment. The combination of a strong pulsed corona/streamer discharge in the water aerosol in the first stage with inoculation of partially dechlorinated (15-30%) processed water with bacteria Pseudomonas mendocina KR1 in the second stage demonstrated as high as 90% dechlorination in the first 40 hours after inoculation, whereas the control (nonaerosol-treated sample) had no chloride ions released, and no bacterial growth. The main features and advantages of the novel two-stage approach, and future plans for research are presented and analyzed.

Ion beam propagation in a transverse magnetic field and in a magnetized plasma

Propagation of a charge‐neutralized ion beam, in a transverse magnetic field (Bz <400 G) and in a magnetized plasma, has been studied. Measurements indicate that the beam propagation mechanism is due to the E×B drift in the region of high β (1<β<400), where β is the ratio of beam kinetic energy to transverse magnetic field energy. Diamagnetic measurements, both internal and external to the propagating beam, confirm the fast diffusion of Bz into the beam on a time scale much shorter than the beam rise time of 10−7 s. When the beam is injected into a magnetized plasma the electric field is shorted to a degree that increases with increasing background plasma density. When the plasma density reaches 1013/cm3 (∼200×the beam density) complete shorting occurs and the beam is deflected by the transverse magnetic field.

Control of the Rayleigh–Taylor instability in a staged Z pinch

Z-pinch experiments and computer simulations provide evidence for enhanced stability and current transfer in a staged Z pinch, consisting of an annular krypton shell imploding onto a deuterium gas fill. Visible-streak and Schlieren imaging provide evidence for a multilayer implosion where the outer plasma shell is Rayleigh–Taylor unstable and the inner plasma column is stable. Computer simulations indicate that the discharge current diffuses through the unstable, outer Kr shell. As the discharge current layer implodes onto the deuterium, current is transferred and a stable implosion results, producing a deuterium-compression ratio of 200.

Laboratory facility for magnetospheric simulation

The magnetospheric simulation facility at the University of California, Riverside (UCR) has been recently modified to improve scalings based on magnetohydrodynamic (MHD) theory. In this facility a magnetized plasma stream interacts with a downstream dipole magnetic field simulating the Earths magnetosphere. Specific improvements include : higher stream-flow velocity, increased plasma density, more intense background and dipole magnetic fields, and improved diagnostic capability. This paper briefly discusses MHD scaling requirements and measurements that are relevant to the laboratory simulation ; including a set of time-resolved, visible-light images showing the evolution of the model magnetosphere.

Faraday rotation in a multimode optical fiber in a fast rise-time, high magnetic field

A magneto‐optic Faraday rotation diagnostic was implemented on a Z‐pinch driven flux‐compression generator to measure line‐averaged, megagauss, axial‐magnetic fields up to 1.6 MG with rise times of 30 kG/ns. The axial‐magnetic field rotated the plane of polarization of a 2‐W argon laser beam in a 0.725‐mm‐diam, fused silica quartz fiber mounted coaxial with the Z pinch. The rapid rise time and the high radiation environment presented by the Z‐pinch plasma caused a high‐pressure impulse <100 kbar, to be coupled into the quartz‐fiber probe disrupting the polarization‐preserving properties of the fiber. The time scale for disruption was characteristic of a shock propagating radially through the fiber to its core. This paper will describe the response of the Faraday diagnostic under these conditions and present a simple model that describes the effects of fiber depolarization that is consistent with previous observations of stress‐induced depolarization in optical fibers.

Staged Z pinch for controlled fusion

A staged Z pinch is considered in which an annular plasma shell made of a high Z material like Kr implodes onto a coaxial plasma target made of a low Z material like deuterium or a deuterium–tritium mixture. The target plasma could be made either by exploding a cryogenically extruded fiber or by filling the annular shell with a gas puff or a plasma puff. Modeling is performed with a two-dimensional (2D) radiation-MHD (magnetohydrodynamic) code. A parameter study is made to determine the sensitivity of this configuration to initial conditions of the shell and the target plasmas. An axial magnetic field is essential for a stable implosion and efficient energy coupling to the final load. Using a 50–50 mixture of deuterium–tritium as a target plasma, the fusion energy gain is optimized by adjusting the initial parameters. The calculations are based on the parameters of the University of California Irvine Z-pinch facility which has a maximum energy storage of 50 kJ.