摘要:

Plasma density profiles are determined by microwave reflection from a modulated dipole probe. The applications of this method to quiescent plasmas and in other plasma explorations are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1713116

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

High‐frequency electromagnetic waves guided by an air‐bounded, axially magnetized, plasma column of radiusaare studied through the technique of parameter space mapping. The parameter space is 3‐dimensional with coordinates &ohgr;p/&ohgr;, &ohgr;b/&ohgr;, andc/&ohgr;a. In this 3‐space, cutoff and resonance loci form surfaces which enclose approximate domains of existence for various classes of waves.Three wave classes, characterized by distinctive cutoff and resonance surfaces, are identified for a magnetized plasma column, and their relation to waves in a boundless plasma, and on a column of small radius (quasistatic waves) is investigated. Also, evidence is found for the continued existence of the surface wave class into the regime &ohgr;b>&ohgr;p.Parameter space analysis leads to a determination of salient dispersion characteristics for all wave classes and all order of azimuthal variation by a method contributing to physical insight but which avoids exact but laborious numerical computation. Waves are found which change from forward to backward or vice versa with increasing wave number.

ISSN:0021-8979    

DOI:10.1063/1.1713117

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Breakdown by thermal instability of a field emitter is analyzed, taking into account the temperature dependence of field emission and of resistivity. Beyond a certain temperature the emission increases while the necessary field drops. It is shown that for a whisker‐like emitter this instability occurs when the emitting tip is only several hundred degrees centigrade hotter than the bulk of the cathode.

ISSN:0021-8979    

DOI:10.1063/1.1713118

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

H2+ions produced by a Philips ionization gauge (PIG) type discharge in hydrogen were injected into a cylindrical electric field which was varied in magnitude to give a maximum strength ranging from 65 to 450 kV/cm. H2+ions in highly excited vibrational states were dissociated by the electric field. The measured fraction of the H2+ions produced by the PIG discharge which were dissociated was 0.0011±0.0002 at a field of 200 kV/cm. Numerous experimental checks demonstrated that the dissociation fraction could not be attributed to effects other than electric field dissociation. The fraction is several times greater than that measured by other investigators. This difference is attributed to the method used in the preparation of the H2+ions.

ISSN:0021-8979    

DOI:10.1063/1.1713119

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The contact potential difference in a low‐pressure thermionic energy converter can be written asCPD=[open phi]˜E−[open phi]˜C, where[open phi]˜Eand[open phi]˜Care averaged work functions of the emitter and collector, respectively. The estimation of[open phi]˜Eand[open phi]˜Cfrom existing work‐function data is discussed. As an example,[open phi]˜Evalues are estimated for well‐aged polycrystalline tungsten wire and those estimates are compared with experimental values.

ISSN:0021-8979    

DOI:10.1063/1.1713120

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The internal modulation of lasers by a variation of cavity losses is analyzed in terms of the normal modes of the system. Time‐dependent perturbation theory is used to describe the results of resistive mode coupling when the losses are modulated with small signals. For the single‐mode oscillator, an expression is obtained for the amplitude distortion in the modulation index of the light produced by a coupling‐type internal modulator when the losses are modulated at a frequency commensurate with the separation between longitudinal modes of the laser cavity. Low distortion is obtained when the modulating frequency is noncommensurate with the longitudinal‐mode frequency separation. The internal coupling‐type modulator in its present form can providesmall amountsof modulation over bandwidths limited to the separation between adjacent interferometer cavity normal modes.For a multimode oscillator, modulation of the internal losses at a frequency equal to the separation between adjacent longitudinal modes produces a pulse‐modulated output wave. The average intensity is unchanged and the peak intensity is increased over the intensity of the unmodulated laser by a factor equal to the number of oscillating modes.

ISSN:0021-8979    

DOI:10.1063/1.1713121

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The origin of moving striations has been investigated by measurement of striation propagation at a sharp change in tube diameter, by study of the relationship between anode spot oscillations and moving striations, by observation of anode spot oscillations at the cutoff current for moving striations, by use of an auxiliary discharge to suppress anode potential oscillations, and by study of a striation system isolated from electrodes. The experiments indicate that: (a) the striation frequency, velocity, and wavelength all change discontinuously at a change in tube diameter; (b) visible spot oscillations are accompanied by oscillations in discharge potential, and exist unchanged above the critical current for disappearance of moving striations; (c) anode oscillations and anode spots may be suppressed by operation of an auxiliary discharge to the anode; (d) the striation frequency synchronizes to an applied oscillation at the anode, provided the applied frequency is close to a small integral multiple of the natural striation frequency; and (e) a striation system can be maintained in a vessel separated from the electrodes by narrow tubes operated above the local critical current for moving striations. No oscillations can be detected in the isolating regions either photoelectrically or with electrostatic probes.It is concluded that: (1) anode oscillations and moving striations are independent phenomena; and (2) moving striations do not constitute the response of the discharge to an external perturbation, but appear to result from a local instability in the positive column.

ISSN:0021-8979    

DOI:10.1063/1.1713122

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Thermionic diodes containing xenon at 1 Torr and cesium at 10−6−10−3Torr can lead to higher diode currents than those with either gas alone at the given pressures. Negative resistance thermionic diodes result from xenon in the appropriate pressure range plus cesium.

ISSN:0021-8979    

DOI:10.1063/1.1713123

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An experimental tube to obtain accurate and reproducible data relating to the efficiency of the hollow cathode discharge had a cathode of two plane‐parallel plates with variable separation, and a movable anode to eliminate the anode fall region. The cathode temperature was kept between 25° and 35°C by employing pulse techniques. Preliminary studies performed in helium and neon at pressures between 2 and 15 Torr gave the following results: (a) The transition from the plane cathode discharge into the hollow cathode discharge is a smooth function of the cathodic plate separation. (b) For each tube current and pressure there exist two or more optimum values of the cathodic plate separation for which the tube voltage has a minimum. The optimum distances depend on type of gas, pressure, and tube current. (c) For fixed tube current, the relative maximum decrease in tube voltage with respect to the plane‐cathode discharge voltage is, in most cases, larger in helium than in neon. (d) The variations of the discharge voltage and current with pressure are consistent with the Townsend scaling law for certain values of cathodic plate separation.

ISSN:0021-8979    

DOI:10.1063/1.1713124

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The velocity of 180° domain walls in BaTiO3crystals with saltwater electrodes has been measured from 3° to 75°C at applied fields from 0.2 to 200 kV/cm by repeated partial switching and etching. Heating the crystal was found to lower the field required to attain any given wall velocity by a factor which is substantially the same for all wall velocities (or for all applied fields) and is determined wholly by the temperature change. The factor is about 3 for a change from 3° to 75°C. This behavior agrees with the Miller‐Weinreich mechanism of thermally activated wall movement. Domain shapes are found to be very rounded at 50° and 75°C, becoming almost exactly circular at 75°C around 1 kV/cm, in marked contrast to the well‐known square domains at 25°C and below.

ISSN:0021-8979    

DOI:10.1063/1.1713125

出版商:AIP    

年代:1964

数据来源: AIP