摘要:

The propagation of finite amplitude waves in a magnetized plasma, in which thermal motion and collisions are neglected, is studied for arbitrary direction of propagation. Solutions for oblique propagation are presented, which complement the analytical solutions for propagation perpendicular to the magnetic field obtained by Adlam and Allen and others, and for parallel propagation obtained by Saffman. Oblique propagation is much more complicated than the two limiting cases in that: (1) In a given direction and at a given speed higher than the Alfve´n speed there are a large number of different waves and (2) As shown by Saffman there are additional waves whose speed is less than the Alfve´n speed. These submagnetic waves are investigated in the limit of infinite mass ratio, and the results compared with computer calculations. The stability of the waves against the two‐stream instability is investigated and it is shown that (1) The supermagnetic waves (speed higher than Alfve´n speedvA) are destroyed by the two‐stream instability unlessvA/cis sufficiently large (2) The submagnetic waves are destroyed by the two‐stream instability unless the pressure is non‐negligible.

ISSN:0031-9171    

DOI:10.1063/1.1711061

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The two‐stream instability in a cold plasma in a very strong magnetic field is considered. The density distribution is assumed to be the same for all species and varies arbitrarily in directions perpendicular to the field. For a given wavenumber in the direction of streaming there is a discrete set of normal modes. The stability of the system is determined by the lowest eigenvalue of a differential equation. A variational principle is devised for this lowest eigenvalue. The variational principle is applied to Gaussian and exponential density distributions. It is indicated how the eigenvalues corresponding to higher modes may be found by a Wentzel‐Kramers‐Brillouin method.

ISSN:0031-9171    

DOI:10.1063/1.1711062

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The low‐frequency electromagnetic conductivity of high‐temperature, low‐density plasmas is examined starting from a linearized kinetic equation of the Balescu type. The equation is solved in the limits &ohgr; ≫ &Ggr;eeand &Ggr;ii≫ &ohgr;, where &Ggr;eeand &Ggr;iiare the inverses of the equipartition times of electrons and ions, respectively. The conductivity is related in a well‐known way to the properties of collective waves, and expressions are obtained for the phase velocity and damping of these waves. The results agree with experiment to just within experimental accuracy.

ISSN:0031-9171    

DOI:10.1063/1.1711063

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An approximate plasma model, using current sheets, is introduced and initial results are presented. The primary utility is to obtain the nonlinear behavior of ion‐cyclotron waves. Linear analysis is used to develop the bicircular particle motion, to show the coupling of the ion‐cyclotron resonance for finiteT⊥, to show Landau cyclotron damping for finiteT∥. The sheet model is developed in terms of vector potentialAand sheet current densityJsforkparallel to the steady field B0. There are transverse fields only, with sheet motion along three coordinates. The electrons are assumed to be hot, forming a neutralizing background. The model accuracy tests show a reasonable duplication of cold plasma ion waves. The first computer experiment shows wave damping forT∥≫T⊥at the rate expected from linear analysis, and withT∥decreasing,T⊥increasing. The second computer experiment shows wave growth forT⊥≫T∥, at the rate expected, and withT⊥decreasing andT∥increasing. The third computer experiment was to find the limit inT⊥for interaction with an electron stream for &ohgr; ∼ &ohgr;ci; the nonlinear limit found is equal transverse energies, whereas linear analysis shows anme/mismaller value. This result is encouraging for using this method for ion heating.

ISSN:0031-9171    

DOI:10.1063/1.1711064

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A kinetic equation for the electron gas which is not subject to the usual short‐range divergence is derived. The method used is the division of the Coulomb potential into a weak part and a short‐range part. The result is expressed as the sum of a Boltzmann integral for the short range potential and a Balescu integral for the ``weak'' part, both of which are convergent. The ``dominant'' terms are identical with those obtained from the usual (divergent) Balescu equation with a cutoff in thekintegration. An expression is obtained for the nondominant (i.e., nonlogarithmic) correction.

ISSN:0031-9171    

DOI:10.1063/1.1711065

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A theoretical study of some nonsteady aspects of microwave radiation on ionized gases is presented. For weakly ionized gases, the concept of ``stabilized'' electron temperature is introduced. It is shown that under certain conditions, ionizations due to microwave radiation may be assumed to take place with the electron temperature remaining at this stabilized value. A simple expression for the ionization rate can then be obtained. Several time scales pertinent to these nonsteady processes have been obtained, and their relative order of magnitude is seen to be crucial in determining the nature of the nonsteady response. One type of nonsteady solutions for the ionization front of the gas under microwave radiation has been considered in some detail. Three different modes of response are possible depending on the initial electron density distributions. In particular, when the initial distribution is of the formbaexp (a&xgr;)/[1 +bexp (a&xgr;)], for &xgr; ≤ 0, whereaandbare constants, the ionization front will propagate in the negative &xgr; direction toward the source of microwave radiation at a constant speed and with the same profile of electron density. This nonsteady response characteristic has some similarity with those observed in shock tube experiments.

ISSN:0031-9171    

DOI:10.1063/1.1711066

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A thermistor bolometer was used to measure the radiation from an argon plasma generated in a plasma torch and exhausted into the atmosphere. Pointwise radiation measurements along the centerline of the plasma jet yielded the axial distribution of radiative flux from the jet. Total radiation measurements revealed that up to 18% of the net power input to the plasma is radiated from the plasma jet. Temperature‐radiation measurements showed the Kramers‐Unso¨ld theory predicts the temperature dependence of radiation reasonably well.

ISSN:0031-9171    

DOI:10.1063/1.1711067

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The problem of neutralizing an ion beam is analyzed within the framework of a one‐dimensional collision‐free theory. The character of steady‐state solutions obtained depends upon the ratio between the mean thermal speed of the electrons and the ion velocity. When the ions are faster, excess electrons are returned to their source from a finite distance behind the electron emitter and the flow of charges is unidirectional (beam‐like) further downstream. When the electrons are faster, a ``floating target'' must be postulated downstream to intercept electrons and ions at equal rates and to return excess electrons to the emitter. In this case the flow pattern of the electrons is ``plasma‐like.'' Both beam‐like and plasma‐like states are found to be unstable with respect to small perturbations. Thus the plasma driving a space vehicle cannot be in a quiescent state.

ISSN:0031-9171    

DOI:10.1063/1.1711068

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Interaction of a partially ionized gas with dust particles was studied. Results generalize the earlier approximation by Rosen.

ISSN:0031-9171    

DOI:10.1063/1.1711069

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A measurement of the electron‐positive‐ion recombination coefficient has been made in air of density near 0.1 atm. and of temperature about 2900°K, yielding the value, &agr; = (4 ± 2) × 10−8cm3sec−1. The results indicate that dissociative recombination, NO++e−→ N + O, is the dominant electron depletion process. Air behind a reflected shock wave at a temperature of 3600°K is expanded rapidly into a thin‐wall quartz tube. The tube serves as a post in three X‐band waveguides. Electron densities are computed from the measured phase shifts of transmitted microwave signals. The relation between electron density and phase shift is determined with discharge plasmas of known electron densities. The recombination coefficient is computed from the measured electron depletion rate and the time variation of the temperature and velocity of the gas in its unsteady expansion down the quartz tube. The effects of diffusion, attachment, and impurities are also investigated. The measured value of &agr; is in reasonable agreement with that of Linet al., at 5000°K when aT−3/2temperature dependence is assumed. This result is also compared with other laboratory measurements near 300°K.

ISSN:0031-9171    

DOI:10.1063/1.1711070

出版商:AIP    

年代:1964

数据来源: AIP