Showing papers by "Edward Ott published in 1976"
TL;DR: In this paper, the relativistic equilibria, the ion current dependence on accelerating voltage, its dependence on applied magnetic field, and its variation due to a velocity distribution of the electrons were determined.
Abstract: The application of high voltage pulse power techniques to the production of intense ion beams is of great interest for plasma confinement, plasma heating, and pellet implosion. The main problem is that application of a high voltage to a simple anode–cathode gap will draw both an electron current from the cathode and an ion current from the anode, and the electrons will receive most of the input energy due to their smaller mass. Two methods of efficient intense ion beam production are considered: (1) the magnetically insulated diode and (2) the ’’reflex‐triode’’. The relativistic equilibria, the ion current dependence on accelerating voltage, its dependence on applied magnetic field (in the first method), and its variation due to a velocity distribution of the electrons (in the second method) are determined. For both methods the ion current can be substantially enhanced with respect to the Langmuir–Child current due to the presence of the negative electron space charge. In the case of magnetic insulation this enhancement increases as the magnetic field is lowered and diverges as it approaches the critical value past which electrons can traverse the gap. For the reflex triode the enhancement is increased by relativistic electron effects and by a population of electrons with energies less than the full voltage across the gap.
74 citations
TL;DR: In this paper, a simplified set of universal fluid equations with no radial dependence was derived, with all parameters scaled out, and analytical and numerical solutions of these one-dimensional equations showed that an initially sinusoidal perturbation grows into a "spindle" or cylindrical "spike and bubble" shape with sharp radial maxima.
Abstract: Sausage instabilities of an incompressible, uniform, perfectly conducting Z pinch are studied in the nonlinear regime. In the long wavelength limit (analogous to the ’’shallow water theory’’ of hydrodynamics), a simplified set of universal fluid equations is derived, with no radial dependence, and with all parameters scaled out. Analytic and numerical solutions of these one‐dimensional equations show that an initially sinusoidal perturbation grows into a ’’spindle’’ or cylindrical ’’spike and bubble’’ shape, with sharp radial maxima. In the short wavelength limit, the problem is shown to be mathematically equivalent to the planar semi‐infinite Rayleigh–Taylor instability, which also grows into a spike‐and‐bubble shape. Since the spindle shape is common to both limits, it is concluded that it probably obtains in all cases. The results are in agreement with dense plasma focus experiments.
23 citations
TL;DR: In this article, the authors calculated the temperature profiles, turbulence levels, and anomalous transport for tokamak discharges using the hypothesis that the dissipative trapped-electron instability drives the plasma to marginal stability.
Abstract: Electron temperature profiles, turbulence levels, and anomalous transport are calculated for tokamak discharges using the hypothesis that the dissipative trapped-electron instability drives the plasma to marginal stability. (AIP)
21 citations
TL;DR: In this paper, the electron and ion current densities in a reflex triode were determined by self-consistently determining the electron distribution function resulting from electron collisions with a foil anode and the potential in the triode.
Abstract: The electron and ion current densities flowing in a reflex triode are calculated. Our analysis self‐consistently determines the electron distribution function resulting from electron collisions with a foil anode and the potential in the triode. The electron and ion currents diverge for a sufficiently thin anode.
9 citations
TL;DR: In this article, the effect of electrostatic trapping on dissipative trapped electron instabilities was investigated in a tokamak-type magnetic well via the mechanism of electric trapping and detrapping by wave electrostatic potential perturbations along B.
Abstract: Three problems related to the effect of electrostatic trapping on dissipative trapped electron instabilities are investigated: (a) the linear theory of the dissipative trapped electron mode for the case in which there is both a magnetic well and an electric well (or anti‐well); (b) the nonlinear stability of a drift wave (in a straight constant magnetic field) whose amplitude is large enough to trap electrons; and (c) the nonlinear saturation of the dissipative trapped electron mode in a tokamak‐type magnetic well via the mechanism of electric trapping and detrapping by wave electrostatic potential perturbations along B.
8 citations
TL;DR: In this article, a non-linear theory of one-dimensional mode-coupling stabilization for the dissipative trapped-electron instability is presented, which couples unstable modes at low wave number to damped waves at high wave number.
Abstract: The non-linear theory of one-dimensional mode-coupling stabilization for the dissipative trapped-electron instability is presented. This non-linear process couples unstable modes at low wave number to damped waves at high wave number. The regions of parameter space in which this process is applicable are carefully specified and the saturated wave spectra and anomalous transport coefficients are calculated numerically for a range of parameters of interest for large tokamak operation. The transport coefficients calculated are appreciably smaller than the usual γ/k2 estimates in moderate- and high-temperature regimes.
8 citations
TL;DR: In this article, the authors considered the utility of ion beams for heating a long thin φ-pinch plasma to thermonuclear temperatures and found that ion beams offer an alternative to previously proposed schemes utilizing CO2 laser beams and intense relativistic electron beams.
Abstract: Motivated by recent advances in the production of intense ion beams, we consider the possible utility of such beams for heating a long thin ϑ‐pinch plasma to thermonuclear temperatures. It is found that ion beams offer an alternative to previously proposed schemes utilizing CO2 laser beams and intense relativistic electron beams.
7 citations
01 Dec 1976
TL;DR: In this paper, the Doppler shift and reflection coefficients for reflection of an EM wave from a moving ionization front in a stationary gas were calculated and used to upshift microwaves to submillimeter waves.
Abstract: The Doppler shift and reflection coefficients are calculated for reflection of an EM wave from a moving ionization front in a stationary gas. It is suggested that this process can be used to upshift microwaves to submillimeter waves.
1 citations