摘要:

The behavior of detector signals corresponding to the thermal desorption of gas from a solid surface for integral‐order kinetics is investigated with respect to variations of the parameters describing (1) the kinetics of the desorption process itself, and (2) the interaction of the desorbed gas with the vacuum system. A computational approach is used because the equations describing the simple model used are, generally, analytically intractable. A computer‐driven display and a data‐logging system facilitate not only the analysis indicated above, but also curve fitting so that the kinetic parameters can be extracted from experimental desorption data containing distortions caused by gas scattering from structures in the vacuum system.

ISSN:0021-8979    

DOI:10.1063/1.1657010

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The magnetic shielding by the heat‐treated superconducting Nb‐40 at.% Zr‐10 at.% Ti hollow cylinder, 5 mm in inner diameter, 9 mm in outer diameter, and 25 mm in length, was investigated at 4.2°K in applied axial magnetic field. The dependence of the magnetic shielding capacity upon the field rate of increase was examined for the samples subjected to the solution treatment at 1100°C for 5 h in vacuum of 10−6Torr and to the heat treatment at 700°C for 3, 10, and 100 h after solution treatment. The magnetic shielding capacity of the sample, heat treated at 700°C for 100 h, was over 17.5 kOe as the magnetic field was applied with its rate of increase of 0.45 kOe/min. A possible phenomenological model estimating the maximum or minimum magnetic shielding capacity was developed by assuming that the flux front in the Bean critical state moves isothermally or adiabatically toward the interior of the hollow cylinder. The calculated value agreed well with the measured value for each sample.

ISSN:0021-8979    

DOI:10.1063/1.1657011

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The saturation magnetization of a 31.4 at.% Ni&sngbnd;Fe alloy has been measured as a function of hydrostatic pressure between 0 and 26 kbar, and as a function of shock‐wave compression between 2.5 and 112 kbar. From the hydrostatic pressure measurements, a zero‐pressure value of the pressure derivative of the saturation magnetization (∂ln&sgr;s/∂P) = −3.15×10−2kbar−1is found. A marked departure from linearity of &sgr;s(P) is seen at higher pressures. This is considered to be due to the slope of &sgr;s(T) becoming steeper and steeper at the ambient temperature as the Curie temperature is depressed by pressure. The shock‐wave compression experiments yield a value of (∂ ln&sgr;s/∂P) = −2.8×10−2kbar−1in the 15–40 kbar stress range.

ISSN:0021-8979    

DOI:10.1063/1.1657021

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Abeles has shown that a marked acoustoelectric coupling can occur due to the penetration of a high‐frequency electric field into a conductor. Calculations are presented here of the coupling due to the spatial phase shift between the Coulomb force on the lattice ions and the reaction force of the electrons, and due to the localized electron reaction on the surface. The latter is largest for diffuse electron reflection, and is the most important coupling mechanism at frequencies above 30 GHz. Efficiencies are fairly low, being in the 10−2to 10−3range under ideal conditions; however, they remain of this magnitude up to the lattice vibration frequency. The model used is approximate: a classical free‐electron model, idealized cases of fixed electron free paths with either uniaxial or isotropic electron motion being considered. For specular surface reflection of electrons, the exact model of Quinn is available for comparison, and it is shown that the results are very similar. Single and multilayered film structures are considered in addition to the semi‐infinite conductor.

ISSN:0021-8979    

DOI:10.1063/1.1657035

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The frequency shift andQchange of a microwave cavity caused by lossy dielectrics or plasma spheres or cylinders is calculated. The necessity for this analysis is prompted by the use of microwave cavities to measure the expansion of nearly spherical plasmas created by focused high‐power lasers. The conditions required for the perturbing volume to behave as if it were a perfect conductor are examined. It is found that much lower conductivities (or permittivities) are required when the perturbing volume is placed in a cavity region where electric energy is predominant.

ISSN:0021-8979    

DOI:10.1063/1.1657048

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The expansion of a laser‐produced blast wave is measured by creating a laser spark at the center of a microwave cavity. The radius measurement as a function of time is accomplished by measuring the cavities' resonant frequency shift. In addition, the blast‐wave surface temperature and electron density can be deduced by measuring the change inQof the cavity. The results are in general agreement with ideal blast‐wave theory.

ISSN:0021-8979    

DOI:10.1063/1.1657060

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Electron‐emission density for LaB6cathodes is compared with that for other common cathode types. Equations for describing the poisoning mechanism are presented. Poisoning is related to the gas pressure, cathode temperature, and heat of adsorption. Posioning was measured with a flowing gas system which maintained a constant pressure in the vicinity of the cathode for varying adsorption rates. Poisoning rates were determined by the cathode temperature and gas pressure. An equilibrium poisoned emission level was reached within a few minutes for each cathode temperature and gas pressure. Poisoning gases used were oxygen, carbon dioxide, air, hydrogen, nitrogen, and argon. Oxygen was the most active poisoning gas and argon the least active. No poisoning results until a critical pressure is reached; the emission then decays rapidly with increasing pressure. Resistance to poisoning increases with increasing cathode temperature. At a cathode temperature of 1570°C, the critical poisoning pressure for oxygen is about 5×10−5Torr. At 1400°C, the critical poisoning pressures are as follows: 2×10−6Torr for oxygen, 2×10−5Torr for carbon dioxide, 5×10−5Torr for air, and greater than 10−2Torr for hydrogen, nitrogen, and argon. On a comparative basis, the critical poisoning pressure for LaB6cathodes is several orders of magnitude higher than the poisoning pressure for oxide and impregnated cathodes.

ISSN:0021-8979    

DOI:10.1063/1.1657092

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The magnetic susceptibilities for neodymium, gadolinium and dysprosium germanides and silicides were measured between about 60° to about 700°K. Plots of 1/&khgr; vsTshow a Curie‐Weiss behavior, but deviations from it are observed below room temperature. The deviations become smaller with decreasing temperature and in most instances tend to approach the asymptote just above the transition temperature. These compounds have theD88structure and a ferromagnetic spin ordering for rare earth atoms in the crystallographic 6(g) sites, and an antiferromagnetic ordering in the 4(d) sites is consistent with the observed behavior.

ISSN:0021-8979    

DOI:10.1063/1.1657101

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The transition from inertia‐limited flow (vacuum) to mobility‐limited flow (high pressure) in gas‐filled diodes is studied theoretically by taking velocity moments of the Boltzmann equation for the electron‐velocity distribution function. It is shown that the momentum‐transfer equation can be integrated when &ngr;c(C), the frequency of elastic collisions between electrons and gas atoms, is independent of the electron speedc, and the hydrostatic‐pressure term is neglected. The resulting current‐voltage (J‐V) curve, which is valid for all gas pressures, reduces to the proper vacuum law (J∝V3/2) at extremely low gas pressure and to the proper high‐pressure law (J∝V2) at high gas pressure, while it is a mixture of the two laws for intermediate gas pressures. The importance of the ratio &ngr;c/&ngr;p, where &ngr;cis the average value of &ngr;c(C) and &ngr;pis the electron‐plasma frequency, is emphasized. It is shown that the current is inertia limited for &ngr;c/&ngr;p<1, and is mobility limited for &ngr;c/&ngr;p>1. It is shown further that mobility‐limited flow divides naturally into two cases, according to whether the electrons retain the energy imparted to them by the electric field or whether this energy is given up in elastic collisions with atoms. The former situation, called the low‐pressure case, prevails when (m/M)1/2&ngr;c/&ngr;p<1, and the latter, called the high‐pressure case, prevails when (m/M)1/2&ngr;c/&ngr;p>1, wherem/Mis the ratio of electron mass to atom mass.

ISSN:0021-8979    

DOI:10.1063/1.1657102

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The voltage (V) dependence of the mobility‐limited electron current density (J) in a gas‐filled diode is calculated for low pressure [(m/M)1/2&ngr;c/&ngr;p]<1 <&ngr;c/&ngr;pas well as for high pressure [1<(m/M)1/2&ngr;c/&ngr;p], wherem/Mis the ratio of electron mass to atom mass, &ngr;cis the average frequency of elastic collisions between electrons and gas atoms, and &ngr;pis the electron‐plasma frequency. It is assumed that &ngr;c(C) is proportional to the electron speedc, which corresponds to the case of an energy‐independent mean free path. It is shown thatJshould be proportional toV3/2p−1d−3for low pressure, and toV3/2p−1/2d−6/2for high pressure, wherepis the gas pressure anddis the (planar) diode spacing. Corresponding expressions for cylindrical geometry are derived and compared with experiment.

ISSN:0021-8979    

DOI:10.1063/1.1657103

出版商:AIP    

年代:1969

数据来源: AIP