摘要:

This investigation is concerned with the development of a low‐inductance, low‐jitter, electrically triggered, high‐voltage annular rail spark gap. Three trigger electrode geometries—blade, dull, and sawtooth edge—are tested for the effects of different field stresses on the spark gap switching performance. All possible polarity combinations are applied to the high‐voltage and trigger electrodes of the rail gap, and the switching inductance and jitter is measured for each case. Finally, the effects of photopreionization from bare sparks on the spark gap switching performance is explored. A switch inductance of 4 nH and jitter of 0.6 ns have been achieved. A practical application of the rail gap is also described.

ISSN:0034-6748    

DOI:10.1063/1.1137887

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

For a multidimensional velocity measurement in fluids laser Doppler optics were developed which permit the switching of the measuring volume during the transit time of a particle by using an electro‐optical modulator. This enables a multidimensional measurement of the flow velocity from only one Doppler burst. The so‐called multicomponent Doppler burst can be detected and processed by only one photomultiplier and one conventional counter. The new measuring technique is demonstrated for an optical configuration which permits a quasisimultaneous two‐component measurement of flow velocity. Experimental results are presented to verify this measuring principle. This new measuring technique reduces the number of optical components and electronic devices compared with a conventional two‐dimensional measuring system using two colors. The range of detectable velocity vectors for usual fringe numbers is shown. Finally, factors limiting the application of this system are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1137888

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The traveling‐wave excitation method has been applied to a helical electrode‐type TE N2laser to increase the laser output as well as to obtain good beam quality. The traveling‐wave excitation was achieved by dividing the discharge into ten sections. The discharge time interval between sequent section can be controlled by the length of coaxial cables. Primary experimental results show that the beam cross section is circular and the output in the direction of the traveling wave is 2.2 times that in the other direction. The laser output with a reflecting mirror is approximately two orders of magnitude larger than that without a mirror. The decrease of laser output with increasing pulse repetition rate has been explained and discussed in connection with the long‐lived nitrogen afterglow phenomena.

ISSN:0034-6748    

DOI:10.1063/1.1137889

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A general purpose photon‐counting interface for use with a minicomputer (NOVA 3/12) is described. This device is capable of signal averaging and autocorrelating digitized data with sample time intervals of fixed or variable duration. Means are provided for experimental control and graphical display of results. Suggestions are given for minor modifications resulting in an even greater performance range.

ISSN:0034-6748    

DOI:10.1063/1.1137890

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Characteristics of the Hamamatsu R1635 10‐mm‐diam photomultiplier have been measured. Some typical photomultiplier characteristics—such as gain, dark current, transit, and rise times—are compared with data provided by the manufacturer. Photomultiplier characteristics, generally not available from the manufacturer, such as the single photoelectron time spread and pulse response for full photocathode illumination were measured and are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1137891

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A microwave cavity suitable for heating a sample to temperatures above 800 °C within 15 s at gas pressures above 17.5 MPa is reported. The cavity is coaxial and operates in the TE011mode at frequencies between 9 and 10 GHz. The heating element is constructed of nickel–chromium (i.e., Chromel) wire. It consists of two concentric helices wound in opposite senses (directions) and connected in series so as to minimize the magnetic field generated by the heater current. The heater is potted in magnesium oxide–phosphate ceramic and placed inside of a cylinder made from 50‐&mgr;m copper foil which provides uniform temperature distribution and shields the heater from the microwave field. This assembly then serves as the heating element and the coaxial conductor of the cavity. The diameter of the coaxial heater assembly is approximately 7 mm. The sample is confined by a cylindrical quartz cuvette which surrounds the coaxial conductor. Sample thicknesses of 0.2 to 1.0 mm can be used. Heating from room temperature to 800 °C requires between 15 and 20 s. Operating pressures up to 17 MPa have been used, although the structural design limit of the brass or beryllium copper walls is greater than 22 MPa. Modulation coils are placed in recessed areas of the cavity walls and covered with a thin layer of copper. Cooling water flows through channels cut into the walls to maintain constant microwave parameters.Qfactors of 8000 –12 000 can be obtained depending on the sample.

ISSN:0034-6748    

DOI:10.1063/1.1137892

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Random and systematic uncertainties in pulsed NMR measurements of nuclear susceptibility are discussed. Methods for minimizing these uncertainties were developed with special reference to ultralow‐temperature applications. Compensation of spectrometer drift and the temperature dependence of the sample circuit using a precision calibrator technique is described. The calibrator was able to compensate for simulated two‐fold reductions in sample coil Q and in receiver gain to within accuracy of 1/2%, and to within 1% for 3‐dB changes in the transmitter output at low levels. Some data‐processing methods are discussed which allow the use of very small rf field pulses to reduce heating.

ISSN:0034-6748    

DOI:10.1063/1.1137893

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A Fourier‐transform ion cyclotron resonance spectrometer (Fourier‐transform mass spectrometer) is described which takes advantage of the speed and flexibility of a substantial array processor. Using this array processor, a preprogrammed instruction stack is read sequentially to generate the sequence of rf excitation waveforms applied to the transmitter plates, and the ion response signal is accumulated, processed, and transformed. Control, programming, storage, output, and display functions are handled by the host minicomputer system. Broadband capability allows data acquisition up to 3.5 MHz, giving the ability to acquire extended mass spectra in one pass. The rapid transforming capability of the processor makes it convenient to acquire frequency‐domain spectra in real time.

ISSN:0034-6748    

DOI:10.1063/1.1137894

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The construction and application of a high‐vacuum deposition system housed in a recirculating, catalytically scrubbed, inert‐atmosphere glove box is reported. This system is specifically applied to the fabrication of tunnel diodes used in a surface vibrational spectroscopy called inelastic electron tunneling spectroscopy or IETS. Through the use of this inert‐atmosphere adsorption/fabrication system, tunneling spectra have been obtained from a variety of air‐sensitive compounds adsorbed on aluminum oxide. Up to now, spectra of some of the species reported here have been unattainable by the adsorption techniques used in IETS. The test molecules employed in this study included TCNE (tetracyancethylene), TCNQ (tetracyanoquinodimethane), and Co2(CO)8. TCNE adsorbed reactively on thin‐film alumina under nitrogen to form a species with a vibrational spectrum similar to that of the TCNE−2ion, while TCNQ appears to form the monoanion under the same adsorption conditions.

ISSN:0034-6748    

DOI:10.1063/1.1137895

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The operational characteristics of a laser‐initiated vacuum spark is studied with reference to its x‐ray emission. The present system employs a fast capacitor bank (current rise time=1 &mgr;s) with input energy of 4.4 kJ. The studies here show that for such a system, the system parameters can be adjusted for satisfactory optimum operation with respect to x‐ray emission reproducibility. It is observed that intense x‐ray point sources are obtained consistently by choosing the rightV–dcombination, whereVis the discharge voltage in kilovolts anddis the electrode separation in millimeters. For the present system, this combination is found to be 20–5 and a x‐ray reproducibility of better than 80% has been achieved in this system.

ISSN:0034-6748    

DOI:10.1063/1.1137896

出版商:AIP    

年代:1984

数据来源: AIP