摘要:

Time‐of‐flight (TOF) analysis of supersonic molecular beams is accomplished by a computer‐controlled TOF analyzer incorporated into a CAMAC module. The measured arrival times are stored in a LeCroy histogramming memory module and transferred to a minicomputer for further processing. The system features four independent multichannel analyzers which can be selected by program. Each unit has 4096 24‐bit channels. Dwell times are programmable between 1 and 255 &mgr;s and the maximum counting rate is 1 MHz. The system is intended for ordinary single pulse or pseudorandom TOF analysis and can also be used in photodissociation experiments employing pulsed lasers. The calibration of the TOF analyzer is described and exemplary measurements are presented.

ISSN:0034-6748    

DOI:10.1063/1.1139604

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report the first implementation of aninsituglow discharge cleaning procedure for the removal of carbon contamination from x‐ray optical surfaces.Insitucleaning obviates the need for the time‐consuming and costly process of element removal, cleaning or repolishing, remounting, and realignment usually necessary to restore x‐ray optics to their original condition. The apparatus required is quite simple and can easily be fitted to most existing UHV (ultrahigh vacuum) mirror boxes or monochromators. Results with several monochromators at the Brookhaven National Labs National Synchrotron Light Source (NSLS) show that better than original performance can be obtained at the carbonKedge, since the elements are not exposed to atmosphere afterinsitucleaning and do not accumulate the adventitious carbon layer associated with more traditional methods. Possible improvements and extensions of the technique are also described.

ISSN:0034-6748    

DOI:10.1063/1.1139605

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We present a procedure to performinsitucalibration of electrical double probes in magnetized plasmas as far as the density is concerned. The procedure does not rely on assumptions of the transport of particles perpendicular to the magnetic field. The comparison of the density as measured by a calibrated probe and by a lithium beam diagnostic in the scrape‐off layer of the tokamak TEXTOR gives good agreement.

ISSN:0034-6748    

DOI:10.1063/1.1139606

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A prototype plasma source spacecraft discharge device has been developed to control overall and differential spacecraft surface charging. Such charging phenomena have contributed to many satellite operating anomalies and systems malfunctions. The plasma source is based on a unique hollow cathode discharge, where the plasma generation process is contained completely within the cathode. This device can be operated on argon, krypton, or xenon and has a rapid cold start time of less than 4 s. The discharge system design includes a spacecraft‐discharge/net‐charge sensing circuit which provides the ability to measure the polarity, magnitude, pulse shape, and time duration of a discharging event. Ion currents of up to 325 &mgr;A and electron currents ranging from 0.02 to 6.0 A have been extracted from the device. In addition, the spacecraft discharge device successfully discharged capacitively biased plates, from as high as ±2500 V, to ground potential, and discharged and clamped actively biased plates at +5 V with respect to ground potential during ground simulation testing.

ISSN:0034-6748    

DOI:10.1063/1.1139607

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A precision ozone calibration system for stratospheric research has been developed and evaluated. Vapor pressures above solid ozone are mixed with a carrier gas (N2) to produce stratospheric ozone mixing ratios at total pressures of 1 to over 20 Torr. The uncertainty in the ozone mixing ratios is approximately ±1.5%, the stability of ozone is ±0.3%. Experiments to be calibrated may sample the gas mixture over a wide range of flow rates; the maximum throughput of gas with corrections of less than 1% to ozone is about 200 Torr l/min. A mass spectrometer system continuously monitors the purity and stability of the N2–O3gas mixture.

ISSN:0034-6748    

DOI:10.1063/1.1139608

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A number of techniques to improve the sensitivity of helium resonance magnetometers is explored. Using a mathematical model of the helium cell discharge and optical pumping process, calculations indicate that substantial gains in sensitivity of a He4magnetometer are possible. The improvements are obtained by use of larger cells and the replacement of the lamp with a laser as the source of pump radiation. A large cell (2 in. diameter×6 in. long) magnetometer with lamp pumping is calculated to have a sensitivity of 3×10−4&ggr;/(Hz)1/2, a value which has been experimentally verified. The projected sensitivity of a laser‐pumped magnetometer varies between 2×10−5and 4×10−6&ggr;/(Hz)1/2, depending on cell size.

ISSN:0034-6748    

DOI:10.1063/1.1139609

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The design of a multiwire gas proportional counter for soft x‐ray detection is described. Position information is obtained over a length of 110 mm from the signal induced in the cathode plane consisting of a delay line. A position resolution of better than 80 &mgr;m is demonstrated in tests performed with fluorescent x rays of well‐defined energies in the range 1.6–6 keV. Count‐rate capabilities reaching 1 MHz are demonstrated in crystal spectrometer measurements of the x‐ray emission from tokamak plasmas. The use of this type of detector in other applications is also discussed, especially in view of the potential of measuring thexyposition over areas up to 110×160 mm2.

ISSN:0034-6748    

DOI:10.1063/1.1139610

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

This paper describes a new technique for measuring post‐arc currents in circuit breakers. The measurements are performed with a specially designed current monitor. In contrast to commonly used current monitors saturation of the core of the transformer at high pulses of current is prevented by shunting the turns of the transformer by antiparallel fast‐recovery diodes. This new device offers several advantages in comparison to other known techniques for post‐arc measurements: there is no galvanic coupling to the network, the system is easy to handle, and the costs of the components are low. The two post‐arc‐current monitors (PACM) described have a sensitivity of 0.1 V/A and 10 mV/A, and are linear within 1% in the range of ±4 and ±100 A, respectively. The first PACM has an upper cutoff frequency of 18 MHz, the second one 3.8 MHz and are designed for sinusoidal fault currents of 6.3 kA and 56 kA, respectively, at a frequency of 50 Hz. Examples of applications to axially blown arcs in SF6and to vacuum circuit breakers are presented.

ISSN:0034-6748    

DOI:10.1063/1.1139611

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A resonance system for comparing low‐value three‐terminal capacitors with an active guard circuit based on an instrumentation amplifier is described in detail. The system is simple, easy to calibrate, and permits precise measurement of lossy three‐terminal capacitors in the frequency range 50 Hz–10 MHz. Dielectric measurements made with this apparatus on 1‐propanol at low temperatures are reported.

ISSN:0034-6748    

DOI:10.1063/1.1139612

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Different configurations of an analog gated base‐line restorer circuit are discussed. An elimination of a ‘‘droop’’ rate is achieved by replacing the analog memory by a digital one. A design employing a digital feedback loop is described.

ISSN:0034-6748    

DOI:10.1063/1.1139613

出版商:AIP    

年代:1987

数据来源: AIP