摘要:

The equations of current continuity have been solved for high‐density (nion>1012cm−3) gaseous plasma as a problem associated with electron‐beam‐controlled electrically excited pulsed laser energy sources. The procedure used first‐order numerical approximations to the space and time development of current and potential gradients. The results of a laser plasma study are (a) the total electron current is not very sensitive to electron emission at the cathode because (b) the sheath multiplies both secondary electrons and cathode current by a large factor and adjusts to current requirement set by electron mobility and density in the plasma. Small changes in the sheath thickness and potential drop satisfy the variable‐current condition set by gas ionization and ion recombination:I=new=ew(S/&agr;)1/2. The potential drop in the sheath of an STP plasma is 400–2000 V for plasma currents of 1–10 A/cm2, and the sheath thickness isd≃0.003 cm.

ISSN:0021-8979    

DOI:10.1063/1.1663553

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We had previously observed, when cosputtering from a single target, that the deposited film was far from uniform, even showing a pattern resembling that of the target. Having subsequently made some energy and power measurements of the negative particles bombarding the anode in a sputtering system, we have concluded that the patterning is due to fast secondary electrons from the target. These secondary electrons are of importance in all types of sputter deposition, since a significant number of them travel in straight lines to the anode without collision. They are responsible for almost all of the power input into the anode and can dominate the growth of a thin film on a substrate at the anode.

ISSN:0021-8979    

DOI:10.1063/1.1663554

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Light scattering from boron trioxide has been studied as a function of temperature in the melt near the glass transformation temperature and in the solid. Both polarized and depolarized spectra were obtained. At all temperatures (20–516°C) the scattering consists of a polarized contribution associated with density fluctuations and a depolarized component presumably connected with the anisotropic nature of the B2O3glass network. Quantitative results are presented confirming that the polarized scattering from density fluctuations in the solid is determined by the equilibrium compressibility of the melt at the fictive temperature. It is shown that the anisotropic scattering also appears to be ``frozen‐in'' at the fictive temperature.

ISSN:0021-8979    

DOI:10.1063/1.1663555

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Metallographic and microscopic techniques have been applied to the study of laser targets of various materials. Optical microscopy and scanning electron microscopy of foils and wires that had been irradiated by a 10‐J laser (wavelength 1.06 &mgr;m) were followed by sectioning through the holes both longitudinally and transversely. Foils of gold and titanium show considerable melting and splatter on the front surface, a hole through the foil, and spalling from the rear surface. Polyethylene shows tensile fracture on the front surface, clouds of large and very small bubbles around the hole near the entering surface, and evidence of the ejection of molten material from the rear surface. In addition, a lenticular void appears near the center of the film. Gold wires, in addition to being ruptured, show a lanceolate void along the axis of the wire extending to well outside the supposed area of influence. As yet only hypotheses for this behavior exist.

ISSN:0021-8979    

DOI:10.1063/1.1663556

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Experiments with two electrohydrodynamic heat pipes are reported. Both devices employ an electromechanical flow structure for axial liquid flow and a capillary wicking structure for (i) collection of condensed liquid at the cooled end and (ii) distribution of this liquid at the heated end. One device has circumferential grooving for the capillary structure and the other has feltmetal wicking. The experiments successfully demonstrate the electrohydrodynamic heat pipe concept. Compatibility of the two circumferential wick structures with an axial electromechanical flow structure is also demonstrated. A significant mismatch of the capillary groove and electrohydrodynamic pumping capabilities results in severe hydrodynamic burn‐out limiting in the first heat pipe. Both devices have very poor over‐all thermal conductances of the order of 1–2 W/°C, reflecting the generally poor heat‐transfer properties of the dielectric working fluids required in electrohydrodynamic heat pipes.

ISSN:0021-8979    

DOI:10.1063/1.1663557

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The specific heat of Li2O·Al2O3·nSiO2glasses and keatite‐phase glass ceramics, withn=4,6,8,10,12 has been measured between 1.5 and 6 K. The temperature dependence of the specific heat was determined by using several least‐squares fits to the data and found to be of the formC=C1T+C3T3. Generally, for a given composition, the magnitude ofC3for the glass ceramic is larger than the value for the corresponding glass. For a given structure,C3also shows a composition dependence. Estimates forC1show a dependence on both composition and structure. The results are compared to those obtained for vitreous silica.

ISSN:0021-8979    

DOI:10.1063/1.1663558

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Laser‐supported detonation waves have been studied with 15‐J 56‐MW/cm2laser pulses from a CO2Marx Bank laser. A smooth spatial and temporal laser beam profile was repeatable from pulse to pulse. Ignition thresholds for laser‐supported detonation waves were determined from relative reflected power and from framing camera photographs for many solid and liquid surfaces. Some of these thresholds were measured as functions of density of the medium (air) from 0.01 to 1 times atmospheric density. The velocities of laser‐supported detonation waves were studied to determine their dependence on laser beam intensity and medium density for conditions above the ignition thresholds of aluminum and lead surfaces. Streak camera photographs displayed clearly defined wavefronts whose initial velocities were constant until they were affected by decreasing laser beam intensities. When the temporal intensity changes in the beam and its focused geometry are included in calculations using the Raizer model for laser‐supported detonation waves to predict the wavefront motion, excellent agreement with the streak camera photographs was found. The initial velocity data are shown to agree with a power law in which velocity is proportional to (intensity/medium density)0.41±0.02. No explanation is proposed for the difference of the power law exponent from the 1/3 value predicted by the Raizer model.

ISSN:0021-8979    

DOI:10.1063/1.1663559

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Helium, deuterium, and neon permeability, diffusivity, and solubility have been measured for CGW‐7740 glass. The results indicate that gas migration occurs primarily through the silica‐rich phase. Reaction of deuterium with the glass structure is evident at temperatures exceeding 300°C. The activation energy associated with this reaction is approximately 15 kcal/mole, which is the same as that for hydroxyl formation in vitreous silica.

ISSN:0021-8979    

DOI:10.1063/1.1663560

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The performance ofn‐type Hg0.8Cd0.2Te (PC) detectors under high optical flux densities was investigated. Detector photoconductivity and response time were measured, in the presence of 10.6‐&mgr;m laser radiation. Flux densities, &phgr;, were varied over four orders of magnitude up to a maximum level of &phgr;=1021photons/cm2sec. For high flux levels the photoconductivity varies as the cube root of the incident flux and the detector response time varies as &phgr;−2/3. It is concluded that the observed saturation in photoconductivity is due to the decrease in carrier lifetime with carrier concentration. The dominant recombination mechanism at high flux levels was determined to be Auger recombination.

ISSN:0021-8979    

DOI:10.1063/1.1663561

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The problem of laser‐induced heating and radial expansion of a low‐density plasma in a solenoidal magnetic field has been examined by means of a Lagrangian computer code incorporating an exact solution of the relevant MHD equations plus thermal conduction. It is shown that for long‐term heating with a realistic range of laser power and magnetic field strength, the resulting radial temperature and density profiles can be closely approximated by a quasistatic solution of these equations.

ISSN:0021-8979    

DOI:10.1063/1.1663562

出版商:AIP    

年代:1974

数据来源: AIP