摘要:

We have devised and programmed a new scheme based on image processing techniques for extracting the intensity of fluorescent display low‐energy electron diffraction spots. The method make no assumptions about spot shape, does not use thresholding, and can deal with badly behaved backgrounds, noise spikes, and dead pixels. All decisions about whether a particular pixel belongs to a spot or to the background are made on purely logical grounds with generally binary operator masks. Once the spot edge has been defined, a local background is subtracted to generate an integrated spot intensity. Extensive tests with diffraction features ranging from very strong to indistinguishable from background by eye show this method to be stable, fast, and reproducible.

ISSN:0034-6748    

DOI:10.1063/1.1144577

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

X‐ray absorption spectroscopy measurements of single‐crystal samples have not been possible due to the appearance of diffraction features in the spectra. To deal with this problem a unique magnetically driven sample oscillator has been designed and built. Its effectiveness in enabling x‐ray absorption spectroscopy studies of single crystals is demonstrated. Furthermore, it is compatible with a cryogenic environment in size, mass, and principle of operation.

ISSN:0034-6748    

DOI:10.1063/1.1144511

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

To support the development of the recently invented capillary‐based x‐ray optics technology, it is necessary to have quick and repeatable precision measurements of x‐ray transmission. A novel fully automated measurement system has been built for this purpose. Measurements are reproducible within half a percent.

ISSN:0034-6748    

DOI:10.1063/1.1144512

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A neutron lens constructed with polycapillary glass fibers is used to focus a 50×45 mm2beam exiting a cold neutron guide onto a spot of 0.53 mm (full width at half maximum) with a current density gain of 80. The characteristics of the lens are presented. This lens is designed to enhance the detection limit and lateral resolution for prompt gamma activation analysis using cold neutron beams.

ISSN:0034-6748    

DOI:10.1063/1.1144513

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Analytical solutions for the temperature distribution and displacement field gradients in the high heat load monochromator are presented. The footprint of the incident x‐ray beam on the crystal surface is approximated by an infinitely long narrow strip, which is applicable in the case of the inclined diffraction geometry. The two‐dimensional problem in the cross section of the crystal normal to the footprint is considered. The solutions for the temperature distribution and displacement field gradients are found in terms of Fourier integrals. These expressions are also valid for x‐ray mirrors. The deviation of the incident beam from exact Bragg position produced by this deformation is calculated. All numerical examples are calculated for the special undulator which is to be installed in the sector III of the Advanced Photon Source.

ISSN:0034-6748    

DOI:10.1063/1.1145199

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A spatial imaging vacuum ultraviolet (VUV) spectrograph has been constructed for simultaneous observation of spatial and spectral distributions of plasma radiation in the wavelength range 150–1050 A˚. The spectrograph consists of an entrance slit of limited height which provides spatial resolution, an aberration‐corrected concave grating with varied spacing grooves which gives a flat‐field spectral output plane, and an image‐intensified two‐dimensional detector system. The basic characteristics of the spectrograph have been investigated by ray‐tracing calculations. The expected performance has been confirmed through experiments using a dc glow discharge source on the reciprocal dispersion, the spatial resolution, or the incident angle dependence of spectral images. VUV spectra with spatial and time resolution have been obtained successfully in the GAMMA10 tandem mirror experiment.

ISSN:0034-6748    

DOI:10.1063/1.1144514

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Reconstruction techniques have been developed to obtain 2D images of plasmas from the electron cyclotron emission (ECE) and soft x‐ray emission signals by taking advantage of the large toroidal rotation rate on the tokamak fusion test reactor (TFTR). From the numerical examination using the sawtooth crash model, we found that the rotational tomography is effective if the crash time is longer than the two rotation periods.

ISSN:0034-6748    

DOI:10.1063/1.1144515

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A technique is presented by which the Fowler–Milne spectroscopic method can be applied to thermal plasmas containing two or more atomic elements. The technique requires the measurement of the emission coefficient for an atomic transition of each element. These values are normalized to the maximum emission coefficient for each transition in the respective single‐element plasmas. Neither calibration of the sensitivity of the apparatus nor knowledge of atomic transition probabilities is required. The technique allows the relative concentration of the elements to be derived significantly more precisely than other spectroscopic methods. The technique is applied to the measurement of the radial profiles of temperature and composition of free‐burning arcs in mixtures of argon and nitrogen. Significant demixing is observed, with the direction of the demixing depending on the relative concentrations of argon and nitrogen.

ISSN:0034-6748    

DOI:10.1063/1.1144516

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An interferometer/polarimeter has been developed and tested for operation on the TdeV tokamak. The system operates at 393.6 &mgr;m on 7 channels equally spaced over the plasma diameter. The interferometer has operated routinely for six years and is used for density feedback control on TdeV, with very little supervision and maintenance. A sensitivity of 2.5×10−16m−2and a response time of 5 &mgr;s enables small density perturbations (&Dgr;n≥0.005n¯e) and fast transients to be resolved. With the appropriate choice of assumptions and boundary conditions, the system can supply credible electron density profiles together with their temporal evolution, using as isocontours the flux surfaces obtained from equilibrium calculations. When operated as a polarimeter, the system now routinely provides current‐density profile measurements as well. Optical cross‐talk between channels, identified as the main obstacle to the extension of the interferometer to polarimetry, was mastered using optical isolation techniques. The system can now resolve, on each chord, a Faraday rotation of 1.5 mrad, limited by vibration, cross‐talk and deflection. Using a parametric approach, poloidal field and current‐density profiles, as well as the axial safety factor and internal inductance of the discharge, are made available after each shot. The apparatus will be used for current‐transport, MHD‐equilibrium and current‐drive studies on TdeV.

ISSN:0034-6748    

DOI:10.1063/1.1144517

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A real time visualization system for the shape of a tokamak plasma cross section has been developed by using Versa Module Europebus (VME)‐standardized modules. Digital signal processors (DSPs) are used in parallel for magnetic analysis. A fast and high resolution graphics control processor is adopted for part of the display system. Fast shape identification methods are presented in which tabulated Green’s functions are utilized. The analysis errors are evaluated with Hitachi tokamak 2 (HT‐2) experimental data. The plasma shape is visualized in real time with the cycle time of 30 ms. When this system is applied to the International Thermonuclear Experimental Reactor (ITER), the estimated cycle time for visualizing the plasma shape is 40 ms.

ISSN:0034-6748    

DOI:10.1063/1.1144518

出版商:AIP    

年代:1994

数据来源: AIP