摘要:

An analytical model has been developed to describe the operation of simple and concentric gas‐loaded heat pipes and to assess the extent of deviations from ideal behavior due to diffusion, viscosity, and sonic flow. The model predicts, with reasonable accuracy, the start‐up power, the maximum heat transport, and the thermal regulation (=&Dgr; density/&Dgr; input power). Experimental results will be presented for Li/He heat pipes. This approximate analytical model should enable spectroscopic and kinetic heat pipe users to design and operate heat pipes optimally without extensive and costly computer solutions of the full Navier‐Stokes equations. The model is based on approximate solutions of diffusion/convection equations, in which the convective velocity distribution of a nearly ideal hat pipe is assumed to be identical to that of an ideal heat pipe. The vapor is treated as a one‐dimensional compressible fluid. Among the more important results are (1) The start‐up powerQSU, defined as the power required to bring the metal vapor density to 95% ofn0, the stagnation density, at the exit of the heated zone (or adiabatic zone if present) is virtually independent ofn0. (2) For a heat pipe whose thermal losses are dominated by radiation, the start‐up power varies asT9/40, whereT0, the stagnation temperature, is defined byn(T0)=n0. (3) The sonic flow limitQCFmay be approximated asQCF= 1/2hfgAn0c(T0), wherehfgis the heat of vaporization per atom,Ais the cross‐sectional area, andc(T0) is the speed of sound atT0. (4) The thermal regulation properties of a concentric heat pipe may be approximated from the thermal regulation properties of simple heat pipes.

ISSN:0021-8979    

DOI:10.1063/1.328256

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A theory for the accumulation of damage in one dimension in fast deformation of a brittle material is developed. The theory is consistent with thermodynamics and takes crack inertia into account. The problem of damage accumulation due to a step pulse in strain is solved, and shows good agreement with experimental results.

ISSN:0021-8979    

DOI:10.1063/1.328257

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The mathematical problem of transient currents that are produced by space‐charge swarms after they are injected into liquids or gases is solved using a field‐independent mobility model for the charge carriers. Only one species of charge carrier is assumed to be present in the fluid‐containing drift space defined by parallel‐plane constant potential electrodes. An integral‐differential equation is derived for arbitrary initial charge distributions in the drift space. From its solution, the transient current waveform can be determined. When the initial current is in a steady state, the integral‐differential equation reduces to a nonlinear ordinary differential equation which is valid for initial currents that may or may not be space‐charge limited. This final equation is solved for the special case of small space‐charge fields. The analysis is also expected to apply to conduction in solids in some cases.

ISSN:0021-8979    

DOI:10.1063/1.328258

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Sidescatter of CO2laser light from underdense, laser‐heated plasmas in H2and He is observed at &Vthgr;=90°. Spectrum, exponentiation, isotropy, and polarization measurements are used to deconvolve two separate mechanisms: (1) Doppler‐shifted reflections from moving dielectric discontinuities created in the laser‐ionization process, and (2) Stimulated Brillouin scattering seeded by these reflections. The dielectric sidescatter is unpolarized and azimuthally symmetric, similar to the diffuse component of scattering in solid‐target experiments. The Brillouin sidescatter saturates at a low level corresponding to an ion wave amplitude of 0.1–1.0%, consistent with previous data on the saturation of backscatter.

ISSN:0021-8979    

DOI:10.1063/1.328215

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Space‐charge‐limited heavy ion beams have been produced by utilizing the plasma blowoffs generated by 20‐MW bursts of 1.06‐&mgr; radiation from an activeQ‐switched Nd:Yag laser. Laser power densities near a moment 1011W/cm2on solid targets generate thermalized plasma plumes which drift to a 15‐kV gridded extraction gap where the ions are extracted, accelerated, and subsequently electrostatically focused. The spatially defined ion beams are then magnetically analyzed to determine the charge‐state content in the beams. Results are presented for the more significant amounts of charge statesZ?5 contained in the beams formed from carbon, aluminum, copper, and lead targets. The extraction and acceleration technique preserves time‐of‐flight (TOF) information in the plasma drift region, which allows plasma ion temperatures and mass flow velocities to be determined from the Maxwellian ion curve TOF shapes for the individual charge species.

ISSN:0021-8979    

DOI:10.1063/1.328216

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Intense relativistic electron beams (1 MV, 125 kA, 50 nsec) launched from foil and foilless diodes have been used to heat mirror‐confined hydrogen plasmas of density 2×1013and 1.6×1014cm−3. Electrical shorts in the foilless diodes were prevented by locating the diode outside the magnetic mirror in a region of lower plasma density. The plasma heating by the foilless diode was found to be slightly greater than that of the foil diode. This agrees qualitatively with the theory of Thode which predicts that foil scattering decreases the strength of the beam‐plasma interaction. E/T;8052.40.Mj, 52.50.Gj, 07.77.+p, 61.80.Fe

ISSN:0021-8979    

DOI:10.1063/1.328217

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We describe an apparatus which forms a hollow cylindrical plasma shell of 3×2 cm2cross section 40 cm in diameter by injecting a neutral gas shell of argon via supersonic injection nozzles and ionizing this shell with a high‐voltage electrical discharge.

ISSN:0021-8979    

DOI:10.1063/1.328218

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The cathode sheath in a cold‐cathode Penning discharge operating in the high‐pressure mode has been investigated by using an rf impedance method. The effect of the presheath lying between the sheath and the plasma has been taken into consideration in deriving the sheath parameters from the impedance of the discharge, measured at two frequencies, under various discharge conditions. The sheath thickness and the dc incremental resistance of the sheath are found to decrease with the discharge current (the static magnetic field being held fixed), while these parameters decrease first, and then remain almost unchanged, if the magnetic field is increased (the discharge current being kept constant).

ISSN:0021-8979    

DOI:10.1063/1.328219

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Thin amorphous (&agr;) films of silicon created by ion implantation have been studiedinsituwhile undergoing the amorphous to crystalline transformation in the electron microscope. The specimens were prepared in such a manner that the amorphous/crystalline interface was viewed edge on and its advance during annealing was readily observed over distances of several microns. Growth rates and activation energies were measured. The active role that defects play during the regrowth process was also studied. An additional advantage of the technique was that in a single specimen different segments of the recrystallization front advanced along several different growth directions simultaneously, hence the effect of regrowth direction on the interface migration rate and defect formation was graphically displayed in a single specimen.

ISSN:0021-8979    

DOI:10.1063/1.328220

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Growth and structure of tellurium films deposited by molecular beam technique onto NaCl single‐crystal and glass substrates were studied by TEM. It was observed that films deposited onto NaCl substrate have a structure similar to those obtained by other workers. The films deposited on glass at a substrate temperature of 150 °C have an altogether different structure showing a definitec‐axis orientation with needle‐shaped crystallites lying parallel to the substrate plane.

ISSN:0021-8979    

DOI:10.1063/1.328221

出版商:AIP    

年代:1980

数据来源: AIP