摘要:

Cyclotron‐resonant laser‐induced gas breakdown has been studied for the first time in the transverse geometry, using 1.222‐mm13CH3F laser radiation propagating perpendicular to the magnetic field axis. The line shape of absorbed laser radiation versus magnetic field near electron cyclotron resonance (87.75 kG) indicates a strong dependence of the line shape on the focused laser intensity. This dependence is not predicted by the standard equilibrium theory of high‐frequency gas breakdown in a magnetic field. We have developed an analytic theory to explain the observed line shapes. The theory takes into account the laser propagation characteristics, in particular that there is nonuniform ionization due to strong resonant absorption of the laser radiation in a length comparable to or shorter than that of the laser focal volume. The transverse geometry simplifies the theoretical analysis because the observed line shapes are not significantly affected by Doppler broadening. Extensive data have been obtained on the fraction of laser pulse energy absorbed in the gas breakdown volume as a function of magnetic field, helium gas pressure, and incident laser pulse energy. Good quantitative agreement is obtained between the observed laser pulse absorption line shapes and the nonuniform ionization theory.

ISSN:0021-8979    

DOI:10.1063/1.325694

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The heating and growth of a spark channel producing minimum‐energy ignition of a propane‐air mixture is investigated. The form of the light signal emitted during the initial stage of ignition is derived. The role of spark energy in contributing to stable burning is discussed.

ISSN:0021-8979    

DOI:10.1063/1.325695

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We have developed a nondestructive assay of the fule content of deuterium‐tritium (DT) ‐filled microballoon laser fusion targets, which is based on &bgr;‐particle counting rates. Using a model employing transmission measurements of kilovolt electrons through thin films, observed count rates are correlated with the amount of tritium in the glass walls and hollow interior of the microballoons. It has been shown that gas pressure in balloons can be calculated from tritium content and a knowledge of the initial gas composition since D and T were found to leak at the same rate. This assay technique is primarily applicable for balloons with glass wall thicknesses <1.5 &mgr;m where the number of escaping &bgr; particles is large compared with the number of x‐ray photons generated in the glass. The technique has been applied to measure the pressure retention characteristics of individual targets. At room temperature, the balloons exhibited widely diverse and rapid leakage rates which could not be correlated with a model based on molecular diffusion and the assumption that all balloons had a homogeneous composition. Cryogenic storage greatly reduced the leakage rates with pressure retention half‐lives ranging from 5 to approximately 12 years. Finally, it was determined that tritium in the glass wall is trapped and evidence is presented to support the hypothesis that it is uniformly distributed across the shell.

ISSN:0021-8979    

DOI:10.1063/1.325696

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The breakdown of a positive point to plane gap in air near atmospheric pressure begins with the formation of a low‐conductivity filament by the space‐charge‐controlled streamer process. Within the filament, the rate of electron attachment exceeds that of ionization, and the external current decreases. However, a sudden rise of current leading to spark breakdown can be observed. The following explanation is proposed. Owing to the current flow the temperature increases within the discharge. A radial flow of neutral species will thus appear, which decreases the neutral density near the discharge axis. In turnE/Nincreases until the ionization rate becomes greater than that of attachment, leading to the final current growth.

ISSN:0021-8979    

DOI:10.1063/1.325697

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The equations of energy, continuity, and momentum are solved to give axial and radial values of temperature, pressure, and axial and radial velocity for vertical arcs stabilized by natural convection. It is assumed that the electric field is purely axial and magnetic forces are neglected. For a free‐burning arc of 10 A in air, calculated temperature and velocity profiles are in good agreement with published experimental results. For an arc in an enclosed vertical tube of mercury vapor, results of central velocities as a function of axial position for a 2.9‐A arc are in good agreement with the experimental results of Kenty. Comparisons are made of the differing properties predicted for free‐burning arcs of 10 A in air, sulfur hexafluoride, and hydrogen. Removal of the maxima in the thermal conductivity has a negligible effect on the degree of predicted arc constriction in SF6. Convective flow in all calculations is assumed to be laminar. The influence of radial pressure variations is found to be almost negligible.

ISSN:0021-8979    

DOI:10.1063/1.325698

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In the present paper we have investigated the excitation of a plasma wave of frequency &Dgr;&ohgr;=&ohgr;1∼&ohgr;2in a collisionless hot plasma by two coaxial Gaussian EM beams of frequencies &ohgr;1and &ohgr;2and propagating in the same direction. The mechanism of nonlinearity is assumed to be ponderomotive force arising because of Gaussian intensity distribution of the beams. In the presence of two beams, the nonlinearities introduced by two beams are additive if the difference frequency &Dgr;&ohgr; is comparable to &ohgr;1or &ohgr;2and, hence, cross focusing occurs. For a given power of one beam, the nature of self‐focusing becomes considerably modified by changing the power of the second beam. The power associated with the excited plasma wave, which depends on the background electron concentration and the intensity of the two beams, becomes drastically modified with the distance of propagation. The theory presented here is also applicable to a slightly inhomogeneous collisionless hot plasma within the WKB approximation.

ISSN:0021-8979    

DOI:10.1063/1.325683

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The spatial and temporal behavior of the x‐ray emission from laser‐produced aluminum plasma was deduced from space‐resolved x‐ray lines and satellite spectra and from a comparison between spectra observed from both sides of thin (1–25‐&mgr;m) foils. The Li‐, He‐, and H‐like ion species were found to have different spatial and temporal behaviors. The evolution of the plasma from the ionizing regime to steady state is also followed. The meaning of electron temperature values deduced from various spectral line ratios is discussed.

ISSN:0021-8979    

DOI:10.1063/1.325684

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The stability of a glow discharge in rare‐gas mixtures containing a small fraction of attaching species is examined, using the e‐beam‐sustained KrF laser discharge as a generic example. The stability limit is shown to lie near the peak of the voltage‐current characteristic, while the mode of instability is dependent on external circuit parameters. The calculated maximum discharge voltage is in good agreement with experimental observation over a wide range of e‐beam current densities.

ISSN:0021-8979    

DOI:10.1063/1.325685

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Annealing of indium and antimony implanted into silicon at doses sufficient to produce an amorphous layer (1014–1015ions cm−2) has been studied using high‐energy Rutherford backscattering. Annealing of these amorphous layers followed the behavior reported for layers formed by silicon ion bombardment and has a pronounced influence on both the retention and lattice‐site location of the impurities, with marked differences between substrates of (111) and (100) orientation. Following epitaxial regrowth on both orientations at 550 °C substitutional concentrations in excess of the solid solubility were observed. Impurity redistribution was not detected at this annealing temperature nor for 940 °C annealing of (100) and (110) substrates, but migration toward the surface was observed after high‐temperature annealing of (111) material. This resulted in a loss of ∼60% of implanted In after 1 h annealing, whereas antimony accumulated behind the native thermal oxide. Impurity atoms continued to migrate after lattice annealing had ceased, and it is proposed that the extended defect structure, which is unique to amorphous layers on (111) substrates annealed at high temperatures, provided the means for this out‐diffusion. Two‐step annealing of (111) material at 550 and 940 °C resulted in a stable impurity distribution, consistent with the absence of this defect structure.

ISSN:0021-8979    

DOI:10.1063/1.325686

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Electrical properties of recrystallized amorphous silicon layers, formed by BF+2implants or Si++B+implants, have been studied by differential resistivity and Hall‐effect measurements. Electrical carrier distribution profiles show that boron atoms inside the amorphized Si layers can be fully activated during recrystallization at 550 °C. The mobility is also recovered. However, the tail of the B distribution, located inside a damaged region near the original amorphous‐crystalline interface, remains inactive. This inactive tail has been observed for all samples implanted with BF+2. Only in a thicker amorphous layer, formed for example by Si+predamage implants, can the entireBprofile be activated. The etch rate of amorphous silicon in HF and the effect of fluorine on the recrystallization rate are also reported.

ISSN:0021-8979    

DOI:10.1063/1.325688

出版商:AIP    

年代:1979

数据来源: AIP