摘要:

The problem of equilibrium and stability of plasma confined in certain magnetic fields of combined mirror‐cusp form is discussed. These fields have the properties that they are nowhere zero and everywhere increase toward the periphery. Attention is drawn to the importance of the existence of closed surfaces of constant |B|—the magnetic isobars. The conditions for plasma equilibrium are derived and interpreted; then by exploiting the existence of closed magnetic isobars certain low‐&bgr; confined equilibria are constructed. These equilibria are shown to be stable according to the fluid (double adiabatic) energy principle and according to the small Larmor radius limit theory. A direct proof of stability against motions which preserve the magnetic moment is given. These equilibria have the property that there is no current along lines of force so that they are also immune to several drift instabilities.

ISSN:0031-9171    

DOI:10.1063/1.1710984

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Two types of hot plasmas were produced and confined between magnetic mirrors by plasma injection followed by slow magnetic compression in the Table Top III device: (1) a ``hot‐electron plasma,'' in which the plasma was highly compressed and the electron temperature was 10 to 25 keV, and (2) a ``hot‐ion plasma'' in which the compression was less but the ions were hotter than the electrons. In both cases, regimes could be found in which gross instability occurred. The plasma column was observed to leave the axis and spiral, as a whole, outward to the chamber walls with a radial velocity of about 5 × 105cm/sec. On the basis of the observations and a comparison with theory this behavior is interpreted as a simple azimuthal mode numberM= 1 interchange instability accompanied by a rotation arising from the fact that the plasma has a net charge. No multiple flutes (M> 1) have been observed during this motion, although occasionally simultaneous existence of two plasma columns has been detected. The lower critical density for the onset of the instability was approximately that density for which the Debye distance was equal to the plasma diameter. Stabilized regimes were also obtained by operation with high injected densities or at higher base pressures and the plasma remained confined for many milliseconds. There was also an intermediate regime in which instability could be deliberately ``triggered'' by a finite electrostatic perturbation in a plasma that had been quiescent for milliseconds. Some aspects of the observed stabilization, particularly the nonobservance of multiple flutes, occurring under conditions in which simple hydromagnetic theory predicts instability for all values ofM> 0, seem to be explainable in terms of a ``finite‐orbit'' theory, although other effects seem also to be present.

ISSN:0031-9171    

DOI:10.1063/1.1710985

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An analysis is made of a conservative trapping mechanism in a static mirror field. The discussion is specialized to the tangential injection of particles in the midplane. The analysis is based on single‐particle dynamics in a conservative system. The adiabatic conditions are violated in two distinct ways: A random exchange of energy between transverse and longitudinal motion can occur due to fast characteristic loops in the particle trajectory; a second‐harmonic angular perturbation in the midplane field produces parametric resonance in the longitudinal degree of freedom and results in energy transfer from transverse to longitudinal motion. Energy tends to be absorbed in the longitudinal degree of freedom until the resonance conditions are no longer satisfied. This tendency toward the accumulation of energy in longitudinal motion arises from the asymmetry of the equations of motion; energy is transferred to longitudinal motion by virtue of an unstable solution of the Mathieu equation and in the opposite direction by ordinary resonance. Computer studies of the coupled nonlinear equations of motion of a single particle verify the analytic prediction of rapid growth of the longitudinal oscillation.

ISSN:0031-9171    

DOI:10.1063/1.1710986

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A particle which moves perpendicular to a magnetic field while undergoing periodic elastic collisions with a rigid wall emits radiation which is rich in higher harmonics. Collisions with a sheath, instead of a wall, also produces radiation of this sort. The resulting radiation is calculated utilizing a simplified model of a sheath and also assuming an exponential plasma density distribution, and is then compared with experiment. One can fit either the observed spectral shape or the observed intensity, separately, but a simultaneous fit is rather difficult. The best results are obtained for a sheath thickness of the order of a Debye length.

ISSN:0031-9171    

DOI:10.1063/1.1710987

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The equations of hydrodynamics, derived by Irving and Kirkwood for short‐range interactions, are here derived for a classical system with Coulomb interactions. The stress tensor, energy density, and energy flux density each consist of a kinetic term, a self‐consistent field term, and a correlation term. The correlation terms are meaningful for systems whose correlation length is small compared to the macroscopic scale of length. No restriction is placed upon the density of the system, nor upon the time scale.

ISSN:0031-9171    

DOI:10.1063/1.1710988

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The Onsager phenomenological coefficients are calculated for coupled electrical and thermal fluxes in a ``weakly ionized'' cesium plasma, when the only collisions of importance are those between electrons and neutral atoms. The phenomenological coefficients are converted into (a) isothermal electrical conductivity, (b) thermal conductivity in the absence of an external electric field, and (c) thermal conductivity in the presence of an external electric field. Numerical values of the ratio of the thermal conductivity to the product of temperature and electrical conductivity compare closely with the theoretical Wiedemann‐Franz ratio. The ratio as calculated is temperature dependent, however.

ISSN:0031-9171    

DOI:10.1063/1.1710989

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An exact solution of the collisionless Boltzmann equation is presented that describes a slab of plasma contained in a magnetic field that is uniform external to the slab. The magnetic field dips in the plasma due to the diamagnetic currents in the plasma sheath separating the region of nearly constant density from the vacuum region. The currents are given by the distribution functions for ions and electrons and the fields obey Maxwell's equations. The solution has the qualitative features of real collisionless laboratory plasma distributions. The problem of a cylindrical plasma with axial magnetic field is also treated, and a solution presented for a limiting case. The solution to the slab problem is charge neutral. The limiting case in the cylindrical problem is also charge neutral, but the general cylindrical problem is not, and contains radial electric fields. The solutions have the merit of being substantially more simple than others that have previously been found for the plasma sheath problem.

ISSN:0031-9171    

DOI:10.1063/1.1710990

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The oscillations of a capillary jet of finite electrical conductivity in the presence of a uniform axial magnetic field are investigated for general perturbations. The dispersion relation is obtained and examined under various limiting cases of electrical conductivity; in particular, for the case of high resistivity an approximate formula for the frequency of oscillations of the jet is obtained. It is found that for nonaxisymmetric perturbations, the modes of oscillation of the jet are always stable and damped. The damping constant of the oscillations for different values of the wavenumber are tabulated for the casem= 1.

ISSN:0031-9171    

DOI:10.1063/1.1710991

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The superposition of anl= 3 helical field on the uniform confining magnetic field of the Model C Stellarator introduces a rotational transform of up to 58° at 5 cm radius. Measurements have been made of the effect on the plasma of superimposing this helical field on the confining field. If the confining field of the stellarator is made ``symmetric'' (if each line of force is closed when no helical field is applied), superimposing the helical field improves plasma equilibrium and increases the plasma temperature and particle confinement time. When the rotational transform from the Ohmic heating current is in the opposite sense to that from the helical winding, such that the net transform near the outer edge of the plasma is zero, a rapid loss of plasma occurs. The effect of a deliberately introduced lack of closure in the vacuum field is minimized by the helical field.

ISSN:0031-9171    

DOI:10.1063/1.1710992

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The fact that the current sheet in a coaxial plasma accelerator is planar with the center conductor negative, and bullet‐shaped when the center conductor is positive can be at least partially explained by a combination of Hall currents and plasma vortices, both of which should be expected to occur in such an accelerator. This explanation asserts that the peculiar asymmetrical behavior of this accelerator is a consequence of the fundamental property of ordinary‐matter plasma: that electrons are light and positive ions are heavy. The sign of the asymmetry would be changed if antimatter plasma were employed. It is doubtful whether a planar current sheet could be achieved with a positronium plasma.

ISSN:0031-9171    

DOI:10.1063/1.1710993

出版商:AIP    

年代:1963

数据来源: AIP