摘要:

A new cavity perturbation method for measuring dielectric properties is demonstrated. Transmission line theory is used to analyze a typical cavity perturbation experiment and show that waveguide impedances can be measured by standard resonator techniques. Cavity perturbation measurements of the impedance of a dielectric post provide a useful method for determining dielectric properties, particularly when the dielectric constant and/or conductivity is large. The transmission line analysis is used to evaluate the ‘‘quasistatic’’ field approximation commonly used in cavity perturbation theory. Application to experimental measurements on Si:As near the metal‐insulator transition is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.336921

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A method is described for investigating the spatial and temporal characteristics of the potential well held responsible for collective acceleration of ions by relativistic electron beams. The method is based on direct probing of the potential well with an externally generated ion beam probe, observing the deflection of this probe with a scintillator‐image converter streak camera system. In addition, time‐resolved magnetic spectrometer measurements of the collectively accelerated ions are described. Time resolution is achieved by using a plastic scintillator and a fast streaking camera as the spectrometer’s detector. Examples of measurements are presented and the potential and limitations of the methods are discussed.

ISSN:0021-8979    

DOI:10.1063/1.336922

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Even though PbSnTe–PbTeSe superlattice has a type‐I’structure, its multiquantum well (MQW) laser has been realized by introducing band bending in the MQW active region. The MQW laser showed anomalous temperature dependence in the threshold current and the corresponding output photon energy. The lasing mechanism and anomalous behavior of the laser is qualitatively well explained by taking into account the variation of band bending due to large temperature dependence of the dielectric constants, assuming the barrier height &Dgr;Ec=−40 meV.

ISSN:0021-8979    

DOI:10.1063/1.336923

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The application of acoustic microscopy to the nondestructive evaluation of mechanical parts in their bulk is somewhat limited by the need for a great number of lens probes (in order to analyze the sample over its whole thickness). A zooming device is proposed here, which enables the continuous testing over the whole volume of bulky samples. A simplified theoretical analysis of the focusing properties of this device is given and the experimental results obtained in the detection mode are reported.

ISSN:0021-8979    

DOI:10.1063/1.336924

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

It is known that the usual development of the mixing length approach to the transport of a passive physical quantity in a turbulent fluid is only valid if the proportional change in concentration of the quantity over a mixing lengthlis small. In the present paper we formulate a modification of the theory which is not subject to this constraint and proceed to apply it to various cases of interest. The results obtained can differ substantially from those given by the usual approach when the above criterion for the validity of the latter is not satisfied.

ISSN:0021-8979    

DOI:10.1063/1.336925

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The characteristics of high‐temperature and high‐energy‐density plasma beams in a ‘‘gas tunnel’’ were experimentally clarified. A strong vortex flow at a high flow rate forms a radial pressure distribution with a sharp gradient. This produces a ‘‘gas tunnel’’ in the center, where the pressure is very low. In this study, this type of gas tunnel was applied to the production of plasma, and high‐temperature and high‐energy‐density plasma beams were easily obtained. The plasma arc produced in this gas tunnel has a higher temperature and electron density than a conventional plasma arc because of a strong thermal pinch effect. Measurement of the properties of this plasma arc was primarily carried out by means of spectroscopy, and it was found that almost fully ionized plasma was obtained in the gas tunnel even at a small current of 200 A. In addition, a temperature of more than 3×104K was achieved by increasing the arc current. A plasma jet generated in the gas tunnel has a very high electrical potential gradient of more than 40 V/cm and high thermal efficiency, and it is relatively easy to obtain an extremely high power of more than 200 kW.

ISSN:0021-8979    

DOI:10.1063/1.337047

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A series of measurements carried out with the point‐to‐plane symmetry has shown that positive corona confirms the Townsend relation while for the negative corona this happens only at large point‐to‐plane distances (greater than 1.5 cm). In this case, the ratio of the prefactors in Townsend relation, for the same geometry, approaches the expected constant (the ratio of the mobilities) at larger distances, around 6 cm. For distances below 1.5 cm, the square root of the current is linear with the voltage, with an intercept of ∼1.4 kV. The results are interpreted as giving evidence of an electronic component at small distances, as suggested by Sigmond. The characteristics change to Townsend at higher distances when the electronic component becomes small as compared with the ionic one.

ISSN:0021-8979    

DOI:10.1063/1.336926

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The soft x‐ray spectra from Au plasmas in 0.1–1.6 keV range and x‐ray conversion efficiencies of Au (highZ) and Al (lowZ) targets with three laser wavelengths of 0.26, 0.53, and 1.05 &mgr;m are measured. In addition, the intensity dependence of the x‐ray conversion efficiency at 0.26 &mgr;m is obtained for Au targets. For 0.26‐&mgr;m laser light, the conversion efficiency of Au targets can be as high as 80% at an intensity of 2.4×1013W/cm2.

ISSN:0021-8979    

DOI:10.1063/1.336927

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Near‐surface modifications of Si induced by reactive ion etching (RIE), such as surface residues and a disordered Si near‐surface region, have been studied by He ion channeling. The dependence of the surface residue layer thickness/composition and the Si surface disorder intensity on the etching gas (mixture) used, the plasma exposure time, and the applied rf power density were investigated. For the case of SiO2/Si selective etching (Si etch rate low), thicker surface residue layers were formed and the Si near‐surface disorder was more intensive than for a nonselective RIE process. In selective SiO2/Si etching, both Si substrate disorder and surface residue layer thickness increase initially with plasma exposure time of the substrate. The intensity of Si substrate disorder was found to increase with greater self‐bias voltage (caused by more rf power) applied during etching. A thermal annealing study showed that the observed Si disorder must be due to several distinct silicon defect states and is not equivalent to amorphized Si. The deposited C,F‐layer thickness was found to depend on the ion bombardment possible during reactive ion etching; above a certain ion energy threshold C,F‐layer deposition is suppressed. Various approaches to recover high‐quality Si surfaces following RIE were evaluated. Due to the complexity of the near‐surface modifications caused by plasma exposure of a Si specimen, simple thermal annealing is ineffective in restoring the surface properties. Promising recovery techniques for device‐quality surfaces were found to be O2RIE and O2annealing post‐RIE treatments. Possible difficulties of the channeling method in the characterization of dry‐etched Si were demonstrated by the observation of ion‐beam‐induced surface impurity desorption and surface‐roughness‐related Si surface peak areal density changes.

ISSN:0021-8979    

DOI:10.1063/1.336928

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Recently, experiments have shown that relativistic electrons in a pinch diode, which strike the anode near the axis, have an angular distribution that is almost entirely within 30° of the normal. Analysis of numerical simulation results provides an explanation of the observed angular distribution. The small angles result from the fact that the electrons are strongly decelerated by a large potential gradient that exists just below the anode center. The resulting population of cool electrons can then be swept up by the axial electric field and redirected to the anode with small angles of incidence.

ISSN:0021-8979    

DOI:10.1063/1.336929

出版商:AIP    

年代:1986

数据来源: AIP