摘要:

Plasma electron heating was accomplished by exciting plasma oscillations with a pulsed, 10‐kV, 1‐A electron beam drifting in a longitudinal magnetic field of 100 to 1000 Oe. The oscillatory energy gained by plasma electrons leads to an increase in their density and mean kinetic energy. The resulting plasma, which is called the ``beam‐plasma discharge,'' is an rf discharge in which a beam‐plasma interaction generates the rf fields.At the beginning of a beam pulse, beam electrons generate a plasma by ionization of the background gas. Within a few microseconds excited plasma electrons become the dominant ionization source. This paper describes the transient rf oscillations that appear in the first few microseconds of the beam pulse. From a detailed study of this transient it was concluded that a nonconvective instability initiates the oscillations, which first appear at the electron cyclotron frequency, and that a convective instability at the plasma frequency generates the oscillations that sustain the discharge.

ISSN:0021-8979    

DOI:10.1063/1.1729220

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The dynamical equations which govern the simultaneous flows of heat and electricity in crystals express the electric and heat current densities as linear combinations of the gradients of the electrochemical potential and the temperature. When a magnetic field is applied, the coefficients in these equations become functions of the applied field. Magnetic field effects are included by expanding the coefficients in powers of the magnetic field. For isotropic media, expansion of the electrical and thermal conductivities and the Seebeck coefficient to the first order in the magnetic field gives the Hall, Righi‐Leduc, and Nernst coefficients, respectively. The resulting dynamical equations have been solved assuming (a)&rgr;,&kgr;,Sare not functions of position or temperature,H≠0, current densityJis either parallel or perpendicular to the temperature gradient ▿Tand to the heat current densityQ; (b)&rgr;and&kgr;not functions of position or temperature,H=0,J∥▿T.

ISSN:0021-8979    

DOI:10.1063/1.1729221

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Single‐crystal (ZnY) (Ba2Zn2Fe12O22) was used in an investigation of the effects of surface finish on the linewidth and high‐power properties. Measurements indicate that by polishing rough‐ground spheres with successively finer grit abrasives, the linewidth can be reduced from 50 to 13.8 Oe. From the measured threshold field, the spin‐wave linewidth (&Dgr;HK) of 6.6 Oe has been calculated, in good agreement with that obtained by Green and Healy who used the parallel pump technique. Experiments indicate a threshold field an order‐of‐magnitude lower than for yttrium iron garnet with a comparable linewidth.

ISSN:0021-8979    

DOI:10.1063/1.1729236

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

In the present paper, an analysis of laser action in semiconductors is made, and a condition for population inversion is established. The radiation output is found to be proportional to the deviation from the equilibrium value of the occupancy of the allowed states including the states in the conduction and valence band and also the donor and acceptor states. Possible laser levels are discussed.Following the general analysis, a scheme is proposed for laser action in covalent semiconductors where the top of the valence band and the bottom of the conduction band do not occur at the same value ofk. The scheme consists of simultaneously tunneling electrons into the (000) valley of the conduction band and injecting holes into the valence band. The outstanding feature of the proposed scheme is that it offers a definite possibility for separate amplitude and frequency modulation of the laser output. Various losses associated with the proposed scheme are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1729237

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The thermionic constants of UO2, UN, USi2, USi3, UB2, UB4, UC, UC&sngbnd;ZrC, and evaporated films of U on W have been determined using a pulsed strong‐field Schottky method within the temperature range of 1200° to 2400°K. The results are consistent with the hypothesis that a film of uranium on the surface activates all of these compounds. This surface film can be provided by a natural excess of uranium in the compound, from a chemical reduction by the base metal, or by evaporation from an external source. The resulting active state for all of the compounds can be described within a factor of 2 or 3 by the empirical Richardson constants &PHgr;=3.0 eV, A = 10 A/cm2deg2.

ISSN:0021-8979    

DOI:10.1063/1.1729238

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

An electron beam scanning technique has been devised to measure variations in the surface work function. These measurements indicate a wide patch distribution in the range of 3.25 to 4.5 eV for inactive uranium carbide, which upon thermal activation becomes covered with a surface having a work function in the narrow band of 3.0 to 3.25 eV. The active surface is very sensitive to ambient gases and can be easily poisoned to a value of work function higher than was the case for the inactive state. These results support the hypothesis that a uranium film is responsible for the activation as was suggested by previous thermionic measurements. An analysis of the effect of a nonuniformity in work function on thermionic measurements, shows that experimental Richardson plots or effective work function plots can give highly erroneous results. The magnitude of this error can be determined and is expressed in terms of the spread of the patch distribution.

ISSN:0021-8979    

DOI:10.1063/1.1729239

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A hydrogen arc has been developed which produces a low‐density plasma column. The electrodes of the arc discharge are geometrically arranged such that the plasma drifts through a hole in the arc anode along a flux tube of the confining magnetic field.A differentially‐pumped vacuum system was constructed which achieved a base pressure of 2.5×10−10Torr in the inner liner region while at liquid‐nitrogen temperature. A density of about 1010particles cm−3can be achieved in the plasma column contained in the inner liner region, down field from the arc chamber, with a gas flow of 2 cm3min−1into the arc chamber. At this flow, the pressure in the inner liner rises to 3×10−9Torr. The ion‐to‐neutral density ratio under these conditions is about 30 to 1 in the inner liner region.

ISSN:0021-8979    

DOI:10.1063/1.1729240

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A method is developed which permits a two‐fluid analysis of wave propagation in a magnetoplasma‐filled waveguide including the effects of Hall field, current inertia, space charge, unequal electron and ion temperatures, and diffusion. Maxwell's equations and the two‐fluid equations expressed in one‐fluid notation are reduced to a pair of coupled wave equations for the longitudinal components of the electromagnetic field. Approximate solutions are obtained for uncoupled TE and TM modes of propagation in a hydromagnetic waveguide. Included is a discussion of the effects of pressure, resistivity, displacement current, and current inertia on the dispersion relations.

ISSN:0021-8979    

DOI:10.1063/1.1729241

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A numerical method to solve Poisson's equation with an empirical set of boundary values gives potentials about complicated configurations such as occur in the lenses of electron microscopes. It involves solving an auxilliary induction problem and then solving the integral form of Poisson's equation numerically. The case for cylindrical symmetry has been coded on the IBM 7090 computer and a program developed that evaluates the electron optical properties of lenses possessing this symmetry.

ISSN:0021-8979    

DOI:10.1063/1.1729242

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The effect of a Maxwellian distribution of emission velocities on the longitudinal current density variation in axially symmetric solid beams is investigated to the paraxial approximation. The effects of both longitudinal and transverse initial emission velocities are included. The treatment permits variable magnetic fields and apertures which intercept some of the beam. Some particles may be turned back because all their energy is forced into the transverse motion; the reduction of the transmitted current density is evaluated. A simple illustrative example is given.

ISSN:0021-8979    

DOI:10.1063/1.1729243

出版商:AIP    

年代:1963

数据来源: AIP