Traveling mirror compressor delay line with nonconstant capacitance

The scaling relations for a traveling mirror magnetic compressor [P.M. Bellan, Phys. Rev. Lett. 43, 858 (1979)] having nonconstant capacitance are derived. Varying capacitance (rather than inductance) makes possible a lower impedance device, and hence, higher field levels or faster compression times

Alfvén-Wave Instability of Current Sheets in Force-Free Collisionless Plasmas

If the current sheet between adjacent twisted magnetic flux tubes is sufficiently thin, the electron flow velocity becomes comparable to the Alfvén velocity and can destabilize collisionless Alfvén waves. The threshold for instability in force-free plasmas is calculated for both inertial and kinetic Alfvén-wave regimes. When there is strong magnetic shear, unstable kinetic Alfvén waves can resonantly accelerate ions to energies much higher than the electron temperature

Collisionless reconnection using Alfvén wave radiation resistance

Patchy magnetic reconnection involves transient field-aligned current filaments. The spatial localization, transient time-dependence, and orientation of these current filaments means they must radiate torsional Alfvén waves. Radiation of wave energy does not come for free—it must load the current which acts as the radiative source. This loading (radiation resistance) is proposed as the energy sink required for collisionless magnetic reconnection to proceed. Radiation resistance for both inertial and kinetic Alfvén waves is calculated and, for highly collisionless plasmas, is shown to exceed by a substantial factor both Spitzer resistivity and the effective resistance due to the direct acceleration of electrons (inertial loading). The radiation resistivity is shown to provide the magnetic field diffusivity required for magnetic fields to diffuse across the assumed width of the current filament on the time scale of the reconnection. It is also shown that Landau damping of the radiated waves results in the generation of energetic, field-aligned particles: in the beta << me/mi regime the energetic particles are electrons while in the me/mi << beta << 1 regime, the energetic particles are ions

Alfvén 'resonance' reconsidered: Exact equations for wave propagation across a cold inhomogeneous plasma

Previous discussions of Alfvén wave propagation across an inhomogeneous plasma predicted that shear Alfvén waves become singular (resonant) at the omega = k(z)v(A) layer and that there is a strong wave absorption at this layer giving localized ion heating. In this paper the three standard derivations of the Alfvén 'resonance' (incompressible magnetohydrodynamics, compressible magnetohydrodynamics, and two-fluid) are re-examined and shown to have errors and be mutually inconsistent. Exact two-fluid differential equations for waves propagating across a cold inhomogeneous plasma are derived; these show that waves in an ideal cold plasma do not become 'resonant' at the Alfvén layer so that there is no wave absorption or localized heating. These equations also show that the real 'shear' Alfvén wave differs in substance from both the ideal MHD and earlier two-fluid predictions and, in the low density, high field region away from the omega = k(z)v(A) layer, is actually a quasielectrostatic resonance cone mode. For omega much-lesser-than omega(ci) and k(y) = 0, the omega = k(z)v(A) layer turns out to be a cutoff (reflecting) layer for both the 'shear' and compressional modes (and not a resonance layer). For finite omega/omega(ci) and k(y) = 0 this layer becomes a region of wave inaccessibility. For omega much-lesser-than omega(ci) and finite k(y) there is strong coupling between shear and compressional modes, but still no resonance

Miniconference on astrophysical jets

This miniconference brought together observers of astrophysical jets, analytic and numerical modelers of both astrophysical jets and spheromaks, and laboratory experimentalists. The purpose of the miniconference was to encourage interaction between these diverse groups and also expose the plasma physics community to the interesting plasma issues associated with astrophysical jets. The miniconference emphasized magnetically driven astrophysical jets and consisted of three half-day sessions. The order of presentation was approximately: observations and general properties, experiments, numerical models, and special topics

Ferrite resonance cones

Resonance cones, a phenomenon which has been observed in electrostatic plasma waves, should also exist in magnetostatic waves propagating in ferrites. Resonance cones, the spatial characteristics of the hyperbolic partial differential describing both plasma and ferrite waves, are aligned along the group velocity trajectory and are equivalent to the superposition of an infinity of normal modes. The existence of resonance cones has been overlooked in standard normal mode analyses of ferrite waves, where typically, only one mode is assumed to exist at a time

Comment on "On the Alfvén resonance and its existence" [Phys. Plasmas 2, 340 (1995)]

The validity of the Alfvén resonance concept in a real plasma is discussed since experiments are performed on real plasmas and not on MHD plasmas

Simple system for locating ground loops

A simple low-cost system for rapid identification of the cables causing ground loops in complex instrumentation configurations is described. The system consists of an exciter module that generates a 100 kHz ground loop current and a detector module that determines which cable conducts this test current. Both the exciter and detector are magnetically coupled to the ground circuit so there is no physical contact to the instrumentation system under test

Rotamak confinement-power-current relationships and r.f. loading resistance

The relationships between input power, driven current, energy confinement, temperature and density are examined in detail for existing rotamak experiments. Additionally, the loading resistance presented to the r.f. power supply and the density at which this resistance peaks are calculated (for typical experiments this density corresponds to an optimum operating point since maximum power is coupled to the plasma)