Plasma Disturbances Research Articles

CURRENT PUSHING OF THE OSCILLATION FREQUENCY OF A 6328-Å He–Ne LASER

Increasing the discharge current through a small dc-excited 6328-Å laser changes the index of refraction of the discharge and causes a blue shift of the laser oscillation frequency of ∼1 MHz/mA. The shift is independent of laser cavity tuning and decreases with increasing dc discharge current. Approximate calculations plus other experiments indicate that this shift represents the dispersive effects of the strong 6334-Å and 6402-Å upward transitions from the neon 1s5 metastable level. The residual spectral width and FM noise in stable 6328-Å lasers, especially as compared to 1.15-μ lasers, may be due to plasma disturbances acting through this dispersive mechanism, rather than to microphonic disturbances as commonly suggested.

Plasma factors in schizophrenia.

THE POSSIBILITY of a biochemical lesion associated with schizophrenia has been probed from many directions in recent years, 1,2 and one area which has received considerable attention is that of disturbances in the blood plasma. A survey of the characteristics of blood-borne factors under investigation in a number of laboratories is shown in Table 1. Although the extraction methods and test situations are different for the most part between laboratories, the information concerning the factor shows surprisingly good agreement. Because some of the extracts display similar characteristics, the question frequently arises whether the different laboratories are working with essentially the same factor or dissimilar factors. Comparative tests of plasma factors prepared by two of these groups were undertaken when the Lafayette Clinic invited investigators from the Worcester Foundation for Experimental Biology to come to Detroit to collaborate in an experiment. Exchange of Fractions

Propagation along the magnetic field of a pulse current originated disturbance in a cold two-fluid plasma

The propagation, along the magnetic field, of a point disturbance in a cold two fluid linear plasma is solved asymptotically in various space-time régimes. The main disturbance is a pulse front travelling at approximately the Alfvén speed divided by the electron to ion mass ratio. Its proffle envelope is an Airy function. It oscillates at the mean of the gyro-frequencies and is effiptically polarized. The disturbances remaining behind this front are of two kinds: an oscillation at the sum of the gyro-frequencies which is circularly polarized and represents the ‘extraordinary’ wave, and an oscillation at the ion gyro-frequency which is elliptically polarized with changing eccentricity and orientation of axis.

Laminar hydromagnetic waves of finite amplitude in plasmas of low temperature

The theory of non-relativistic hydromagnetic waves of finite amplitude in a plasma is presented in a simple, but systematic way. The emphasis is on stationary disturbances in a cold plasma. The physical meaning of the cold-plasma model, especially with respect to the description of collisional and collisionless dissipation effects, is discussed.

Propagation and Instability of Transverse Waves in Current-Carrying Electron-Hole Plasmas

The modes of propagation and of convective and absolute instability of transverse disturbances in solid-state plasmas of varying degrees of compensation and mobility anisotropy are calculated for a system with a drift current directed parallel to a static magnetic field. The starting dispersion relation, derived for a Fermi distribution, is also obtainable from the work of Misawa, but approximations valid when the drift velocity (${v}_{d}$) is less than the Fermi velocity make it similar to that of Bok and Nozi\`eres. In addition to helicon and Alfv\'en waves, one of the solutions is a mode of propagation with wavelength independent of frequency as observed by the author in Bi. Tests for absolute instability show two possible modes, one independent of collisions as described by Misawa, and the other resulting from a negative-energy-carrying wave in a positive-resistance background. Under appropriate conditions, depending mainly on the degree of compensation, the latter becomes a convective instability. Amplification of the negative-energy helicon wave is found under some conditions to occur for ${v}_{d}<{v}_{\ensuremath{\varphi}}$ (${v}_{\ensuremath{\varphi}}$ is the phase velocity), and it is noted that the proper criterion for gain, instead of ${v}_{d}>{v}_{\ensuremath{\varphi}}$, is that the negative-energy-carrying wave must see a net positive resistance. Negative resistance can lead to a second mode of amplification, namely that of a normal positive-energy wave, as observed in Bi.

Propagator for Disturbances in a Plasma

The propagation of high-frequency disturbances in an infinite plasma is studied by the method of propagators. The plasma is assumed to be an electron fluid with positive uniform background. The propagator is given explicitly in terms of generalized functions. It possesses a characteristic rear wake behind the head of the wave, attributable to dispersion within the plasma.

Propagation of Hydromagnetic Waves in Collisionless Plasma. I

The propagation of hydromagnetic waves in collisionless plasma is investigated on the basis of the Chew-Goldberger-Low approximation. The dispersion relation for weak, plane disturbances in a uniform plasma is derived. It is found that there exist the fast and slow modes of magnetoacoustic waves as well as the Alfvén wave. However, under certain conditions the phase velocities of the slow and the Alfvén waves become imaginary: namely the system is not necessarily totally hyperbolic but can be partially elliptic. The conditions on the elliptic cases are investigated in detail, especially for the slow wave. Then the propagation of a wave diverging from a point source is investigated graphically as well as analytically. The general theory of steady flow is also given, and some discussions are done for the two dimensional aligned field-flow in which the directions of magnetic field and flow are aligned everywhere.

Propagator for Disturbances in a Plasma

Propagator for Disturbances in a Plasma

Transverse plasma waves and their instability

Linearized equations are derived for disturbances in an infinite plasma without an imposed magnetic field. It is shown that besides the electrostatic, or longitudinal, waves which are usually considered, there can also exist electromagnetic, or transverse, waves. The two sets of waves are generally coupled, but one can nevertheless classify the waves as either mainly longitudinal or mainly transverse. It turns out that a plasma which is stable to longitudinal waves will be unstable to transverse waves unless the velocity distribution of its particles satisfies some rather stringent conditions. In a practical case these conditions would require the distribution to be isotropic.

Erratum to: Magneto-compressional disturbance in a tepid plasma

Erratum to: Magneto-compressional disturbance in a tepid plasma

Magneto-compressional disturbance in a tepid plasma

The propagation of steady state pulses travelling perpendicular to a magnetic field in a cold plasma was originally discussed by Adlam and Allen (1). It was found that pulses exist when the ratio of the pulse velocity to the Alfven velocity exceeds unity. An essential feature of the non-linear pulse theory is that the fields rise exponentially in the region of the undisturbed plasma, a result which may be obtained also from the linearized theory. Guided by this we have examined the steady state problem for a tepid plasma in order to establish whether the plasma is capable of supporting exponentially rising fields. In this article a linear and a quasi non-linear analysis of the problem is given and it is shown that pulses exist when the disturbance speed is supersonic. It is also shown that the range of disturbance velocities, for which pulses are formed, is reduced in a highly non analytic manner.

Spectroscopic observations of `fluctuations' in the Sceptre IV discharge

Attempts were made on Sceptre IV to detect a wave ve locity in the fluctuation of spectral line intensity. In a typical pair of oscillograms, a phase displacement was observed between corresponding features. These observations indicated a plasma disturbance which moves round the torus with a velocity of the order of 5 x 1O/sup 6/ cm/sec, in the opposite direction to the dischange current. The mean values of the velocities measured from prirs of oscillograms were 5.5 x 1O/sup 6/ cm/sec. This phenomenon can be interpreted as being due to a helical instability wave of the type discussed by Ware. (M.C.G.)

Dynamics of classical many-body systems

In Part 1 we discuss the present state of the theory of the propagation of small amplitude disturbances in monatomic gases and plasmas. The analysis is based on kinetic equations for one-particle velocity distributions involving self-consistent field forces and Boltzmann-like collision terms. In Part 2 a microscopic formulation of the classical N-body problem is developed. The theory is used to analyse the meaning of earlier microscopic approaches, and carried to the point where the problem of Part 1 can be treated in a more fundamental way.

Strong hydromagnetic disturbances in a collision-free plasma

Abstract An attempt is made to extend the exact pulse solutions found by Adlam and Allen (1958) at zero temperature to finite temperatures and the heating of the plasma is studiod. A linear treatment shows that the increase in the temperature is small except for very strong pulses. An approximate treatment of the gas pressure is found to be invalid for strong pulses at the experimental values of the initial temperature. Discussion of the ions which start with large thermal velocities shows that some of them are likely to gain energy, but that their effect on the field may be important at the experimental values.

Disturbances in a multi-velocity plasma

The single-velocity treatment of ac disturbances in electron flow is often accurate enough even when the flow actually has an infinitely broad but peaked velocity distribution, such as a Maxwellian or a bell-shaped distribution. In seeking a better approximation, one is tempted to expand in terms of the moments of the velocity distribution and to disregard terms beyond that involving the second moment. This leads to a dispersion equation describing waves which strictly do not exist. A linearized analysis by transform methods predicts a field which oscillates in an exponentially damped manner. This is not the oscillation of a normal mode, however, for various velocity classes of the charge distribution have ac densities which grow with time. This indicates that the linear expression will hold over a finite interval only. A simple example which compares a multi-stream analysis with an analysis based on the charge density in phase space (the distribution function) indicates the same sort of failure of both of the linearized theories at large times. Thus, it appears that the failure is characteristic of the problem rather than of the method of solution. The method of solution is a matter of choice.

BLOOD COAGULATION IN DISSEMINATED SCLEROSIS AND OTHER DISEASES OF BRAIN STEM AND CORD

In 1935 Simon and Solomon 1 published studies on the coagulation responses of the blood in disseminated sclerosis. Their theoretic considerations sprang from the observations of many workers 2 that exacerbations of symptoms in disseminated sclerosis are often related to trauma, operation, exposure, immersion, pregnancy, infection, emotional excitement, etc.—factors cited by Pickering 3 as predisposing to disturbances in the blood plasma and to thrombosis. The hypothesis that a common denominator in these situations might be a disturbance in the coagulation reactions of the blood offers a clinical basis for the observations of Putnam and associates 4 that the lesions in disseminated sclerosis are the result of venous thromboses in the brain and spinal cord. Simon and Solomon 1a found that in both control cases and cases of disseminated sclerosis there was a definite drop in coagulation time after the intravenous administration of typhoid vaccine. They observed, also, a similar, but