摘要:

An electron-beam energy recovery system was experimentally investigated using a multistage electron collector designed by a numerical simulation. In our previous experiments, the potential of each electrode was provided through a voltage divider of several hundred megaohms resistance. Experimentally, it was observed that a part of the beam current was lost to ground through the resistance, and inferred that the electrostatic effect of the electrodes was changed from the initial operating condition. In order to overcome the drawback of voltage divider resistance, two high-voltage power supplies have been provided for the electrodes, and the charge collecting electrodes have been kept at a little higher potential than that of the cathode by using a battery. The recovery currents of the system have been directly measured by an ammeter. The maximum charge recovery efficiency of the collector was almost 100&percent; with a beam current of 0.2 mA. It was, however, seen that this efficiency reduced to 73&percent; for a beam current of about 0.85 mA due to the secondary emission. The maximum energy recovery efficiency, 74&percent;, was calculated for 0.2 mA beam current, and this efficiency was reduced to 58&percent; for a beam current of 0.85 mA. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148827

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe an indirectly heated cathode ion source which has several times the lifetime of commercial Bernas sources which incorporate a bare filament cathode. In addition, much higher multiply charged beam currents are attainable using this source due to its ability to operate safely at higher arc discharge power. In addition to an overall system description, we present typical lifetimes and ion species fractions, and the latter’s dependence on source operating parameters such as arc voltage and source magnetic field. Data are presented for boron, arsenic, and phosphorus beams. Cathode lifetime ranges from 70 h at the highest discharge power levels to over 500 h for moderate operation. At high discharge power levels (≈1 kW), the ions are predominantly atomic, rather than molecular, species. Multiply charged beam production also increases with discharge power and plasma density. Doubly charged fractions of 15&percent; for phosphorus, and 2&percent; for boron, have been demonstrated during ion implant.©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148866

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This article describes a numerical study of the role played by two-dimensional turbulent fluctuations in microwave reflectometry—a radar technique for density measurements using the reflection of electromagnetic waves from a plasma cutoff. The results indicate that, if the amplitude of fluctuations is below a threshold which is set by the spectrum of poloidal wave numbers, the measured backward field appears to originate from a virtual location behind the reflecting layer, and to arise from the phase modulation of the probing wave, with an amplitude given by one-dimensional geometric optics. These results suggest a possible scheme for turbulence measurements in tokamaks, where the backward field is collected with a wide aperture antenna, and the virtual reflecting layer is imaged onto the plane of an array of detectors. Such a scheme should be capable of providing additional information on the nature of the short-scale turbulence observed in tokamaks, which still remains one of the unresolved issues in fusion research. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148828

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A simple electron density diagnostic for low-temperature, magnetized plasmas is described which relies on the propagation angle of lower hybrid waves. Experiments are discussed in which the diagnostic is used to determine residual electron densities in negative ion plasmas. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148829

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Doppler-free two-photon induced fluorescence in the Lyman-&agr; lines of H, D, and T has been suggested previously as a local and isotope-selective diagnostic of the intrinsic neutral hydrogen densities in magnetically confined fusion plasmas. In the present article, it is shown that the diagnostic potential of this method is significantly increased if it is combined with neutral atom beams whose characteristics are such that efficient production of thermal ground state atoms via charge exchange reactions is achieved. Considerably deeper plasma regions than just the plasma edge can thus be probed and local, isotope-selective information (e.g., the H/D/T density ratios) is obtained on the more relevant ions rather than on the intrinsic neutrals. Additional diagnostic possibilities, e.g., those arising from the spectroscopic investigation of the beam particles themselves, are also discussed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148830

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Average, rather than point specific temperature measurement is important in a number of industrial situations. In this work, a method to improve this type of measurement using the fluorescence lifetime-related mathematical parameter, the singular value (SV), is discussed in detail. The analysis reported shows that with rare-earth doped fibers used as temperature sensor probe elements, for average temperature measurement, such a system works well especially when the lifetimes obtained from different sensing probes are very close to each other. The SV scheme, based on matrix theory, is important because the average temperature-dependent singular value possesses the characteristics of both high speed and high precision. Using the method, an average temperature sensing scheme is demonstrated in experiments carried out over the region from 20 to 100 °C, in whichNd3+doped fibers are employed as the intrinsic temperature sensor elements. When two temperature sensing probes are used in the measuring region, the precision determined for the average temperature estimation is±3.6 °C.When three sensors are employed instead of two, the precision is similar at±3.4 °C.Results obtained indicate that with more sensor elements used in the sensing region, the accuracy achieved is not diminished due to the averaging effect in the measurement. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148831

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A device for attenuating weak shock waves propagating in a duct has been developed utilizing sound-absorbent plastic which is usually used for attenuating sound waves. The device has a tube made of the sound-absorbent plastic installed coaxially to a surrounding metal tube with a clearance between them. The clearance acts as an air layer to enhance the performance of the shock wave attenuation. When a weak shock wave propagates through this device, the pressure gradient of the shock wave is gradually smeared and hence its overpressure is decreased. The performance of the device was examined using a1/250-scaled train tunnel simulator which simulated the discharge of weak shock waves created by high-speed entry of trains to tunnels. The overpressure of the shock waves ranged up to 5 kPa. The shock wave overpressure was decreased by 90&percent; with the present attenuator attached. This device can be applied to various industrial noise suppressions which are associated with unsteady compressible flows. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148832

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Based on the light extinction of total internal reflection by triangular prisms, very sensitive detection of the shock front and fast moving free surface has been demonstrated for 1 GPa shock waves in polymers. This is the first experimental verification of the feasibility of the inclined-prism technique for the relatively low shock stress region, which was originally proposed and used by Eden and Wright for obtaining the high-explosive generated shock Hugoniot of several condensed materials. The present method has the advantage that it only requires closing the gap between the free surface of the target and the reflected surface of the prisms. The feasibility and the limitation of the method have been discussed both theoretically and experimentally. A typical streak photograph for a PMMA specimen is shown to compare with the published data. It is seen that the present method is very sensitive for shock arrival detection even in the 1 GPa shock stress region. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148833

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have developed a polyvalent reflection-mode apertureless scanning near-field optical microscope (SNOM) from a commercial scanning probe microscope (SPM). After having explained our motivations, we describe the instrument precisely, by specifying how we have integrated optical elements to the initial SPM, by taking advantage of its characteristics, and without modifying its initial functions. The instrument allows five different reflection-mode SNOM configurations and enables polarization studies. Three types of SNOM probes can be used: dielectric, semiconducting, and metallic probes. The latter are homemade probes whose successful use, as probes for atomic force microscopy, by the commercial SPM has been experimentally demonstrated. Using silicon–nitride (dielectric) probes, one of the five configurations has been experimentally tested with two samples. The first sample is made of nanometric aluminum dots on a glass substrate and the second sample is the output front facet of a laser diode. The preliminary SNOM images of the latter reveal pure optical contrasts. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148834

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A technique for controlling the tip–sample distance in near-field optical microscopes is presented. It consists of mechanically exciting a fiber tip inserted without any adhesive between the two prongs of a highQ-piezoelectric tuning fork. The detection of the shear forces is classically achieved by measuring the decrease of the dithering amplitude when the tip approaches the surface. This simple setup greatly simplifies tip replacement and its resonance frequency tuning. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148835

出版商:AIP    

年代:1998

数据来源: AIP