摘要:

We present a thorough yet simple approach for synthesizing highTcsuperconductors of substantial quality. The approach is accompanied by a step‐by‐step discussion of possible pitfalls as well as a correlation of the sample characteristics to the various preparation procedures. A procedure sufficiently accurate for characterizing the resistance as a function of temperature for aTcdetermination is also described.

ISSN:0034-6748    

DOI:10.1063/1.1139402

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A CO2laser small‐angle scattering experiment has been set up and used for the investigation of plasma density fluctuations in a magnetized plasma. The local oscillator reference beam for homodyne mixing is produced by diffraction from a thin tungsten wire which lies in the main probe beam near the scattering center. The diffraction wire produces a diffraction pattern covering the scattering plane. An angular adjustment of one single mirror in the outgoing probe beam permits easy alignment of different scattering angles and scattering directions. Rayleigh scattering of ultrasonic waves has been used for testing and calibrating the scattering system. First results from plasma measurements are presented.

ISSN:0034-6748    

DOI:10.1063/1.1139403

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

In this article we describe the theoretical motivation and experimental development of low‐energy (2 keV) neutral beams for fueling the central cell of the TMX‐U thermal‐barrier tandem mirror experiment at Lawrence Livermore National Laboratory. Theoretical estimates are given for the beam current required to build up a low‐density plasma (nc=0.5–2.5×1012cm−3) to a final‐state high‐density plasma (nc=1×1013cm−3). The design of low‐divergence (±3°) beam modules is described together with test stand measurements of beam‐neutral current, divergence, and species fractions. Experimental results are given for injection of 45 aA of low‐energy neutral‐beam current into the central cell of TMX‐U.

ISSN:0034-6748    

DOI:10.1063/1.1139404

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A time‐of‐flight diagnostic for analysis of relatively low‐energy ion beams is described. The system incorporates several novel features which improve its performance in a number of ways. The technique is simple and can provide an alternative to magnetic analysis of ion beams for the determination of ion charge state and beam composition.

ISSN:0034-6748    

DOI:10.1063/1.1139405

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new technique for local magnetic field measurement in a bumpy torus NBT‐1M (which is a magnetic plasma confinement device) has been developed using a rapid‐frequency‐scan (RAFS) laser system combined with sodium atomic beam probing. The RAFS laser beam excites the sodiumD1transition in the plasma cavity, and the Zeeman pattern is determined with laser fluorescence spectroscopy in a single laser shot. From the Zeeman splitting, the transient magnetic field distribution in the plasma, produced by electron cyclotron resonance heating (ECH), is measured with an accuracy of ±3.2%, a spatial resolution of 5 mm, and a temporal resolution of 5 &mgr;s.

ISSN:0034-6748    

DOI:10.1063/1.1139406

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A laser deflection measurement system has been developed which is both fast (&tgr;≊20 ns) and sensitive (&dgr;&fgr;≊0.5 &mgr;rad). This diagnostic is capable of sensing and discriminating between electrons and neutral particles in a multicomponent plasma, and yields quantitative results. The technique allows continuous measurements in time. Construction is inexpensive and simple to field. This system is, therefore, highly competitive with traditional techniques in diagnosing the development of transient plasmas.

ISSN:0034-6748    

DOI:10.1063/1.1139407

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A high‐resolution, time‐resolving soft x‐ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics. The basic instrument is a high‐resolution, interferometrically adjusted, extreme grazing incidence Schwob–Fraenkel duochromator. The instrument is equipped with two multichannel detectors that are adjusted interferometrically and scan along the Rowland circle. Each consists of an MgF2coated, funneled microchannel plate, associated with a phosphor screen image intensifier that is coupled to a 1024‐element photodiode array by a flexible fiber‐optic conduit. The total wavelength coverage of the instrument is 5–340 A˚ with a measured resolution (FWHM) of about 0.2 A˚ when equipped with a 600‐g/mm grating, and 5–85 A˚ with a resolution of about 0.06 A˚ using a 2400‐g/mm grating. The simultaneous spectral coverage of each detector varies from 15 A˚ at the short wavelength limit to 70 A˚ at the long wavelength limit with the lower dispersion grating. The minimum readout time for a full spectral portion is 16 ms, but several individual lines can be measured with 1‐ms time resolution by selected pixel readout. Higher time resolution can be achieved by replacing one multichannel detector with a single channel electron multiplier detector. Examples of data from the PLT and TFTR tokamaks are presented to illustrate the instrument’s versatility, high spectral resolution, and high signal‐to‐noise ratio even in the 10‐A˚ region.

ISSN:0034-6748    

DOI:10.1063/1.1139408

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have developed a coherent source of XUV light, which is continuously tunable between 904 and 1024 A˚, and line tunable to 720 A˚. It employs the technique of frequency tripling in a pulsed free jet of gas, and requires a single tunable laser system. Spectra of the relative XUV output vs wavelength in the 904–1024‐A˚ range are presented for the tripling gases Ar, Kr, Xe, CO, and N2. Also listed are relative outputs obtained by tripling at resonantly enhanced lines between 720 and 900 A˚ in Kr, Xe, and CO. Possible improvements to the source are discussed, and examples of its application are given.

ISSN:0034-6748    

DOI:10.1063/1.1139356

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Design criteria for a N2laser withLCinversion excitation circuit are theoretically and experimentally described. Lower resistance, depending on the spark gap pressure, gave higher energy, while the inductance was independent of it. Laser energy increased with higher gas flow rate and was saturated at rates over 10 l/min. Other experimental relationships between pulse width, gas flow rate, energy, and repetition rate are described. Typically, an energy of 4.6 mJ, a peak power of 700 kW, a pulse width of 6.6 ns, and an efficiency of 0.18% was obtained at a repetition rate of 0.4 pps, a gas flow rate 10 l/min, and a voltage of 15 kV. For a higher repetition rate of 10 pps the parameters were 3 mJ, 400 kW, 7.5 ns, and 0.12%, respectively.

ISSN:0034-6748    

DOI:10.1063/1.1139357

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have incorporated a resistive anode, microchannel‐plate based photon‐counting 2D optical imaging detector with standard time‐correlated single photon counting circuitry. The result is a very powerful spectroscopic system which combines the very low dark count and parallel collection capabilities typical of this type of detector with simultaneous time resolution of the individual photon counts. The required timing signal can be generated with a very simple addition to the biasing network of the standard detector, and results in temporal resolution of 500‐ps FWHM, equivalent to that typically obtainable with moderately fast single channel photomultiplier tubes.

ISSN:0034-6748    

DOI:10.1063/1.1139358

出版商:AIP    

年代:1987

数据来源: AIP