摘要:

Multiple reflection of a microwave beam between a horn antenna and a smooth target in the antenna near field produces an interference effect in the received power. This effect can be described by modeling the antenna and target as a closely coupled system with ‘‘coherent’’ reflection coefficients. This model shows better agreement with experimental data than models based on isotropic antenna ‘‘backscatter.’’ Measurement techniques are derived from this new model, which permit, by sampling the interference pattern, the remote sensing of the reflection coefficient of an unknown surface. From the reflection coefficient the dielectric constant or surface roughness can be obtained. A simple diagnostic apparatus is described together with possible industrial/laboratory applications.

ISSN:0034-6748    

DOI:10.1063/1.1144578

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The relative increment of the total flux in a secondary coil is presented as a function of sample magnetic susceptibility, a demagnetization factor, and the secondary coil filling factor caused by the sample. The filling factor was defined and its basic properties were given. The relation between the filling factor and geometric parameters of a spherical sample coaxially placed in a cylindrical coil was determined. The calibration factors, used up to now, and the filling factor, were compared. It was shown, that if the demagnetization factorD→1 (in the case of a thin film placed perpendicular to the magnetic field), and the sample susceptibility &khgr;≠−1, the magnetization susceptibility is not measurable, except in the case when &khgr;=−1.

ISSN:0034-6748    

DOI:10.1063/1.1144579

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An automatic high‐precision ultrasonic system with the corresponding ultrasonic cell is described to measure simultaneously the speed of sound and the attenuation as a function of frequency. The technique is based on the pulse‐echo method and is designed to detect small structural changes in liquids, when an external variable is changed. The precision of the technique is limited by the stability of the temperature, which was kept constant within ±0.5 mK. The method, which permits one to obtain the absolute value of the velocity as well as the attenuation with respect to the solvent, is fully automated for the whole variation of the external variable, which added to its fast response permits easy use in dynamic processes.

ISSN:0034-6748    

DOI:10.1063/1.1144580

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A simple coincidence circuit has been built and attached to conventional pulse counters to obtain the energy distribution of the coincident ion pair arising from the three‐body polar dissociation process H+3+He→H++H++H−. The coincidence circuit is based on TTL components and a solid‐state delay line. A method to derive the true coincidence H+–H−energy distribution is described, from which properties such as the inelastic energy loss and angle of proton ejection can be obtained.

ISSN:0034-6748    

DOI:10.1063/1.1144581

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The design and performance of a secondary emission electron gun with a wire ionized plasma as an ion source is discussed. An electron beam current density of up to 100 mA/cm2is obtained over an area of 55×5 cm2at a cathode voltage of 250 kV in pulses with a duration of about 20 &mgr;s. The current distribution over the beam area is uniform to better than 25%. The achieved combination of pulse duration, beam current, and electron energy is attractive to excite high‐pressure gas laser media. Preliminary results with the utilization of the gun in an electron beam sustained discharge excited atomic Xe laser show an output energy of 1 J/lat a wavelength of &lgr;=1.73 &mgr;m.

ISSN:0034-6748    

DOI:10.1063/1.1144582

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The mean plasma potential was measured on the LBL advanced electron cyclotron resonance (AECR) ion source for a variety of conditions. The mean potentials for plasmas of oxygen, argon, and argon mixed with oxygen in the AECR were determined. These plasma potentials are positive with respect to the plasma chamber wall and are on the order of tens of volts. Electrons injected into the plasma by an electron gun or from an aluminum oxide wall coating with a very high secondary electron emission reduce the plasma potential as does gas mixing. A lower plasma potential in the AECR source coincides with enhanced production of high charged state ions indicating longer ion confinement times. The effect of the extra electrons from external injection or wall coatings is to lower the average plasma potential and to increase thene&tgr;iof the ECR plasma. With sufficient extra electrons, the need for gas mixing can be eliminated or reduced to a lower level, so the source can operate at lower neutral pressures. A reduction of the neutral pressure decreases charge exchange between ions and neutrals and enhances the production of high charge state ions. An aluminum oxide coating results in the lowest plasma potential among the three methods discussed and the best source performance.

ISSN:0034-6748    

DOI:10.1063/1.1144583

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A method of preparing ion beams of known mass and charge for time‐of‐flight scattering and recoiling spectrometry (TOF‐SARS) using sequential deflection pulses (SDP) has been developed. A double‐pulsing sequence is described in which the first pulse is used to create ion pulses and the second pulse, triggered after a suitable delay, allows only the species of interest to be transmitted to the target. A mass resolution ofm/&Dgr;m=3–5 was achieved with the present system, eliminating the need for conventional mass resolution devices when high mass resolution is not required. Examples of the direct separation of Ar+and Ar2+ions from an ion beam and separation of Ar+and Ar2+scattering and recoiling spectra from an indium phosphide (InP) surface are provided.

ISSN:0034-6748    

DOI:10.1063/1.1144584

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

It is shown that the cylindrical symmetry of a charged particle beam can be preserved precisely while it is bent through a single dipole with zero pole face rotations and uniform field, although in one plane the beam is freely drifting whereas in the other plane the beam is focused. The beam conditions at the entrance to the dipole are derived and cast into two analytic formulas. It is shown that symmetry preservation calls for matched beam optical functions (&bgr;,&agr;), that is, matched orientation and amplitude of the beam phase space ellipses into the dipole. The beam conditioning at the entrance to the dipole is discussed and formulated. Some illustrative cases are calculated, and an example design is presented. Finally, it is proved that such a symmetric matched beam may be defined for any system with equal diagonalR‐matrix elements, and the results are applied to another specific case of a parallel sided magnet.

ISSN:0034-6748    

DOI:10.1063/1.1145205

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In order to study ion implantation effects in irradiated powders a rotating wing‐drum apparatus has been constructed. It consists of a conical vessel with wings inside which hosts the powder. The vessel is rotated. The wings lift the powder grains which then drop down through the ion beam line and are hit by the ions. This process is repeated until statistically a homogeneous ion beam treatment is achieved. Setup and features of this technique for agitating powder in an ion beam are described in detail, including different wing drums and an implantation chamber in which the wing drum is mounted. Problems with powder loss and sputtering of the drum rearside are discussed. As an example, results of gold ion implantation and deposition on alumina powder are presented.  

ISSN:0034-6748    

DOI:10.1063/1.1144585

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The ability to produce high quality films in an electron cyclotron resonance reactor is dependent on the gas distribution system. In an effort to understand gas distribution effects, a variety of gas ring injection systems were implemented during silicon nitride growth. Film refractive index, uniformity, and stress were used to gauge each gas distribution system. As a result, we have demonstrated that evenly distributed gas injection systems are the most desirable producing uniform films. Film thickness uniformity was significantly influenced by the design of the gas ring as well as the gas flow. Theoretical models supported the observed results and identified desirable properties for gas ring distribution systems.

ISSN:0034-6748    

DOI:10.1063/1.1144586

出版商:AIP    

年代:1994

数据来源: AIP