摘要:

Standard spark gaps have lower time limits of gap recovery when testing with high repetition rate impulses and in high-current high-voltage multiple impulse testing. More important, they are not suitable for the generation of opposite-polarity successive impulses using conventional capacitive-type generation techniques. In this article, an improved design incorporating two rotating spark gaps is described. The new spark gap was used to test ZnO surge arresters with two successive impulses of currents up to 5 kA and voltages up to 50 kV. Time intervals as low as 10 ms were achieved between the two impulses. Both similar and opposite polarity tests were carried out successfully. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148440

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The definition of the “Quality,”Q, of a count-rate meter algorithm is introduced as the reciprocal of the algorithm’s (&tgr;×&egr;) product, where &tgr; is the response time of the algorithm to a sudden change in the average count rate and where &egr; is the fractional standard deviation of the steady-state measurement of a constant average count-rate pulse stream. Analytical expressions for &tgr; and &egr; of digital rate meter algorithms are used to calculate maximum values ofQfor both linear and exponential algorithms. The values of the basic algorithm parameters necessary to achieve these minimum (&tgr;×&egr;) products are derived for both algorithms. The use of these values results in algorithms that have relatively short response times and, simultaneously, relatively small steady-state errors. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148441

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The frequency of a three-longitudinal mode He–Ne laser was stabilized by the method of detecting the secondary beat frequency between modes. The stabilized laser has been efficiently used as a laser source for a distance meter. In distance measurement, two intermode beat frequencies (875 MHz, 145 kHz) were, respectively, used as a modulation frequency instead of an optical modulator. The resolution of the distance meter was higher than 20 &mgr;m. The total uncertainty was within 20 &mgr;m by correction of errors except for the uncertainty of the refractive index of the air. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148442

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The purpose of this paper is to analyze the operation of a pressure sensor based on an array of collector-assisted field-emission triodes (FETs). The silicon membrane (the anode of the device) put in front of the array is bent by the external pressure, and thus, the field-emission current is modified. An analytical solution has been used to calculate the deflection of the silicon diaphragm when the pressure is applied and a numerical model was developed for the single emitter FET. The array emission current is obtained adding the contributions of all the FETs in the array, no interaction between the emitters being considered. The device sensitivity and resolution have been computed as functions of both the silicon membrane and FET array parameters. Better sensor sensitivity and resolution are obtained for those situations, which assure higher field-emission currents. A simple analytical model was developed for the field-emission pressure sensor, supporting these observations. The obtained modeling results can be further used for sensor design improvement. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148443

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Many molecular beam epitaxy (MBE) applications require a source of ionized gas atoms or molecules. However, the high gas pressures and high kinetic energies associated with many standard gas sources can be detrimental to MBE deposition. These disadvantages are addressed here by an ionized gas source fabricated from a common laboratory ionization gauge. The source described here produces 100 eV gas ions while maintaining vacuums of better than10−8 mbar.This source has the additional advantage of being inexpensive and simple to construct. Design, construction, and operation of the source will be presented. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148444

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A laser Doppler velocimeter employing aCO2laser has been developed by using its optogalvanic effect. A change in the electric impedance of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as much as 60 kHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148445

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A mass gate allows transmitting a selected mass in a time-of-flight mass spectrometer and to block other masses. The conventional stopping-potential mass gate does not discriminate against spontaneous fragments, which are generated in the drift tube. We present a simple improved version of a mass gate, which discriminates against fragments by using the fact that their kinetic energy is lower than that of the parent ion. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148446

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The microphone technique has been applied to the study of laser ablation of a silicon target. The momentum flux of silicon atoms generated by laser ablation at 266 nm was detected both at high vacuum and at background gas conditions. The response of the microphone to an atomic pulse of a few &mgr;s was in agreement with theoretical expectations. The magnitude of the microphone signal increased linearly with laser fluence. A pulsed valve was adopted to also compare the response of the microphone at longer pulse durations. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148447

出版商:AIP    

年代:1997

数据来源: AIP