摘要:

Low‐energy electron diffraction (LEED) has great need for a quick and efficient means of making intensity measurements (e.g., in studying reactive surfaces which quickly degrade, and in handling the enormous amounts of data needed for data averaging). The photographic–vidicon camera method fills this need. This paper describes a system and procedure for this method. We have pointed out advantages of this method over other methods of LEED intensity data collection and analysis, and have included comments on the advantages of our experimental system over other systems using this method. General properties of the photographic and vicdicon system are analyzed as well as specific tests done on the method. Estimates of probable error in spot intensity measurements due to numerous effects have been analyzed and I–V curves reduced from raw photographic data are compared. It is hoped that the description, comments, and analysis will facilitate the incorporation of the photographic–vidicon method of LEED analysis into research programs.

ISSN:0034-6748    

DOI:10.1063/1.1135796

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In discharge‐flow systems employing electron paramagnetic resonance detection, intense spectrometer noise is present under certain conditions. This noise is due to free electrons produced in the discharge and can be eliminated by the addition of an electron scavenger to the flow. Using SF6to suppress the noise, EPR spectroscopy can be used to identify and study transient species within a millisecond after their formation in an electrical discharge.

ISSN:0034-6748    

DOI:10.1063/1.1135797

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A self‐balancing bridge system with a dc current comparator and a superconducting flux‐gated galvanometer is described. The bridge is capable of measuring small resistances (10−4–10−7&OHgr;) at liquid helium temperatures with an accuracy of 1 ppm.

ISSN:0034-6748    

DOI:10.1063/1.1135798

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The design and construction of a mass spectrograph, for the diagnostics of fast pulsed sources, is described. It is intended particularly for measurements on laser generated plasma. The special features of the instrument are a broad energy passband (Emax/Emin=5) and simultaneous energy independent mass‐focusing for a mass range of (m/z)max/(m/z)min=4. The resolutions of the mass and energy spectra, respectively, are (m/&Dgr;m) =30 and &Dgr;&egr;/&egr;=0.01. A theoretical analysis of the ion‐optics is presented together with test results.

ISSN:0034-6748    

DOI:10.1063/1.1135799

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Recent investigations on the mechanism of fretting fatigue have indicated that mechanical damage, not chemical corrosion, has the largest effect in decreasing structural component life. Since there is no general agreement on the mechanism of fretting fatigue, an experiment has been designed to evaluate statistically the relative role of the mechanical process and the chemical process in reducing fatigue life. An initial step was to develop an apparatus that allows fretting fatigue tests to be performed in both laboratory air and vacuum environments. A detailed discussion of the experimental apparatus and experimental procedure are presented in this paper. Also typical test results are presented. It is found that fretting fatigue in vacuum is about ten times slower than that in laboratory air. Fractographic analysis of the wear surface indicated that less severe fretting damage occurred in the vacuum environment.

ISSN:0034-6748    

DOI:10.1063/1.1135800

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The fundamental characteristics of the energy distribution of output electrons from a single channel electron multiplier were studied experimentally in detail for a few types of straight channels. The width of the energy distribution curve, ranging from about 50 to 15 eV FWHM, is found to depend on the applied voltageVAand the length‐to‐diameter ratio &agr; of the channel, and to vary with output current. The results can be explained in terms of the normalized field strength near the output end of the channel and generalized by a set of universal curves presenting the energy width as a function of output current level for different values ofVA/&agr;.

ISSN:0034-6748    

DOI:10.1063/1.1135801

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An electronic stabilization system for an oscillating vane pressure gauge is described. A new continuous drive method is used, obviating the necessity for reliance on mechanical filtering by the vane to produce stable oscillation amplitude. The parameter, damping coefficient, can be measured as being proportional to dc voltage. The dc correction signal is generated with attention to system stability so that stable operation is achieved quickly. Experimental results showing proportionality between the dc correction voltage and damping ratio are presented.

ISSN:0034-6748    

DOI:10.1063/1.1135784

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In this paper we describe a new electronic instrument called a spectrum expander, which is a two‐port digital signal‐processing device whose output power spectrumSout(Ef) is (approximately) a frequency‐expanded replica of its input spectrumSin(f):Sout(Ef) ≈Sin(f), whereEis the expansion ratio (usuallyE>2). When inserted between a signal source and a spectrometer, the spectrum expander improves the effective resolution of the spectrometer, thereby permitting real‐time, high‐resolution measurements to be made. This capability is especially important in radio astronomy, where fixed‐resolution multichannel filter spectrometers are common. Our treatment of the spectrum expander includes a discussion of its basic principles, formulation of design rules, a brief study of random noise and quantization effects, and presentation of data illustrating expander performance. The prototype expander, constructed from Schottky–TTL components, accepts any signal of bandwidth⩽12.5 MHz and expands it to fill a 128‐channel spectrometer with 32‐MHz total bandwidth. Signal degradation caused by processing with the spectrum expander is minimal; the signal‐to‐noise ratio at its output is measured to be ∼0.1 dB lower than at its input.

ISSN:0034-6748    

DOI:10.1063/1.1135785

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The design of a probe‐preamplifier combination which reduces the NMR receiver recovery time following a pulse by a factor of at least twenty at 5 MHz is described. The preamplifier, which has a noise figure of 1.3 dB, employs negative feedback to damp the probe coil (a typical effectiveQis 7), but maintains the signal‐to‐noise ratio that one would expect from an undamped coil. In addition, the use of a short phase‐inverted pulse following the main transmitter pulse serves to reduce drastically the ring‐down of the probe for those high voltages where the preamplifier is inoperative. Optimum utilization of transmitter power in achieving fast pulse rise times is also discussed, as well as elimination of ’’phase‐glitch’’ by proper tuning and the use of a broadband transmitter.

ISSN:0034-6748    

DOI:10.1063/1.1135786

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Hydrogen ion beam optics in a two‐stage linear acceleration system is studied by examining the beam divergence as a function of the voltage and gap distribution, the beam perveance, the background gas pressure, the aspect ratio, and the total accelerating energy (60‐110 keV). The system consists of four electrodes with single, cylindrical, straight‐bore apertures acting as an extraction‐accel–decel column. An optimum relation between the field ratio and the extraction perveance is obtained from measurements for the minimum beam divergence condition. The HWHM divergence angle is <0.3° under optimum conditions. Qualitative agreement between the measurements and a previous theoretical study is noticed. A potential application of the results to high energy neutral beam injectors for fusion research is also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1135787

出版商:AIP    

年代:1979

数据来源: AIP