摘要:

Particle and energy transport in tokamaks and other toroidal confinement devices is dominated by turbulence generated by flows and gradients. In order to understand and control of this transport, diagnostic instrumentation was developed to study the structure and magnitude of microturbulent processes and to identify the origins of plasma loss. This review will cover the primary instruments that have been developed to measure fluctuating quantities associated with transport: density, &dgr;n, temperature,&dgr;T,potential, &dgr;&fgr;, and magnetic field, &dgr;B, and their correlations. The methods discussed are Langmuir probes, heavy ion beam probes, collective and phase scintillation scattering, beam emission and ordinary spectroscopy, reflectometry and enhanced scattering, electron cyclotron emission, and several magnetic methods. The emphasis here will be on techniques applicable to microturbulence whose scale length is greater than the ion cyclotron radius and much less than the minor radius. Limitations and strengths of each method will be described and compared. Techniques will be discussed for estimating fluctuation intensities and wave number spectra or, equivalently, multipoint correlations in radial, poloidal, and toroidal directions. Large scale or magnetohydrodynamic-like plasma oscillations are typically studied with tomographic techniques or external probes and are reviewed elsewhere. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148387

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel system was developed, which allows one to switch the wavelength of a narrow-band excimer laser between two successive light pulses at a repetition rate of at least 250 Hz. This is realized by a periodically driven piezo actuator, which is attached to the diffraction grating of the narrow-band KrF excimer laser. The achieved position accuracy of the grating leads to a wavelength reproducibility of ±0.2 pm, which allows one to apply this system to laser spectroscopic investigations like LIF or LIPF of OH in flames. Using the fast wavelength switching system background reduced concentration and temperature fields in flames can be measured within one sequence. Some possible realized and planned applications like the measurement of gas temperature, the diagnostic of turbulent combustion processes, and the investigation of combustion processes under microgravity are discussed. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148227

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We propose a method to reduce the bandpass of soft x-ray multilayer Bragg reflectors. It consists in etching down to the substrate a multilayer mirror having a large number of bilayers in order to get a lamellar grating with a multilayer bar width representing only 10&percent;–30&percent; of the grating period. The grating is used at the zeroth diffraction order. Once designed, this monochromator was tested with theL&agr;,&bgr;spectra of iron and copper. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148228

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A time-resolved stopped-flow x-ray absorption fine structure (XAFS) system was developed using synchrotron radiation as an x-ray source. The shortest sampling time for time-resolved measurements was on the order of 1 ms with the dead time of ∼5 ms, which was limited by the mixing procedure in the stopped-flow unit and by the drift velocity of the ions generated in the ionization chamber as a detector. The time-resolution ability and the quality of the obtained XAFS spectra were greatly improved in comparison with the laboratory stopped-flow XAFS apparatus previously constructed. The time-resolved XAFS measurements were performed for the reduction reaction of[Fe(CN)6]3−withL-ascorbic acid in an acidic aqueous solution. The rate constants obtained from the XAFS experiments were reasonable judging from the kinetic parameters previously reported. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148229

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A miniature-cavity realization of the cavity ring-down concept, which permits extension of the technique to spectroscopy of surfaces, thin films, liquids, and, potentially, solids, is explored using a wave-optics model. The novel spectrometer design incorporates a monolithic, total-internal-reflection-ring cavity of regular polygonal geometry with at least one convex facet to induce stability. Evanescent waves generated by total-internal reflection probe absorption by matter in the vicinity of the cavity. Optical radiation enters or exits the resonator by photon tunneling, which permits precise control of input and output coupling. The broadband nature of total-internal reflection circumvents the narrow bandwidth restriction imposed by dielectric mirrors in conventional gas-phase cavity ring-down spectroscopy. Following a general discussion of design criteria, calculations are presented for square and octagonal cavity geometries that quantify intrinsic losses and reveal an optimal cavity size for each geometry. Calculated absorption spectra for theNO3radical from 450 to 750 nm in a nitric acid solution are presented to demonstrate bandwidth and sensitivity.

ISSN:0034-6748    

DOI:10.1063/1.1148230

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a new experimental setup for single molecule spectroscopy using a high efficient mirror arrangement with a geometrical efficiency of 0.77. Signal-to-noise (S/N) ratios up to 90 for single pentacene molecules in ap-terphenyl crystal demonstrate that increasing the detection efficiency improves the S/N ratio if the detection geometry ensures a strong stray light suppression. This is realized by the presented mirror arrangement. The experiments were done in a He contact gas cryostat, which is able to work below the lambda point. Temperatures down to 1.7 K at the sample were obtained. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148231

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An intense nitrogen atom beam source of simple construction, with easy handling and maintenance was built and tested. Nitrogen atom beams with an intensity estimated to be1019atom/sr s and with an average kinetic energy of 0.8–2 eV in the forward direction were obtained. This novel atom source can be successfully ignited using pure nitrogen gas and operated stably during several hours of continuous performance. The temperature-rise effect of calorimetric sensors due to the bombardment of the N atom beam was used to analyze the intensities and kinetic energies of nitrogen atom beams. The emission spectra from the arc also show that a high concentration of atomic nitrogen was produced using this source. Experiments such as the nitrogen atom beams interacting with substrates to form a TiON film and a carbon nitride film indicate the high concentration of atomic nitrogen in the beam. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148232

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Micrometer-sized nozzles and skimmers made from drawn glass tubes are described and tested for the production of highly monoenergetic He atom beams. Glass nozzles with diameters between 1&mgr;m and 4&mgr;m when operated at He source stagnation pressures of up to 1000 atm provide intense beams with measured speed ratios ofS=50–100,in good agreement with the predicted behavior scaled from nozzles with larger openings. Miniature glass skimmers with diameters as small as 3&mgr;m were also successfully tested with conventional 10&mgr;m diameter nozzles. These miniature nozzle-beam sources can be used to greatly reduce the size of present-day He-atom surface-scattering time-of-flight spectrometers and to reduce the number of vacuum stages and the size of vacuum pumps. They also open up new experimental possibilities as illustrated by measurements of the spatial profiles of seeded nozzle beams. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148233

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Reactivities of bimetallic clusters can be controlled by varying their composition, making them potentially valuable as catalysts and for use in elucidating the reactivities of such subnanoscale surfaces. A dual rod laser vaporization source coupled to a fast flow reactor is developed for the study of bimetallic clusters and their reactions. In order to establish the versatility of the technique, the results of studies are presented in which Nb/Al clusters are formed in two plasmas induced by the second harmonic (532 nm photons) of a single Nd:YAG laser and then detected by a quadrupole mass spectrometer. The beam from the laser is split and then focused onto each rod, allowing the mixing ratio within the cluster to vary by altering the laser fluence on each rod. With a low fluence on the Nb rod and a high fluence on the Al rod, an Al rich cluster distribution is formed,NbAlm− (m=2–20), andAlm− (m=5–31). By increasing the fluence on the Nb rod and decreasing the fluence on the Al rod, a Nb rich cluster distribution is formed,NbnAlm−(n=3–8andm=1–3),NbnOAlm − (n=3–8andm=1–5), andNbnO− (n=3–8). Additional characterization is also performed on V/Al clusters. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148058

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of the nonideal response characteristics of electrostatic analyzers is described and equations are derived, which allow a calculation of the distortion that this causes in measurements of angular and energy distributions of electrons from atomic collisions, especially in electron impact. Examples are given that show how a contamination as small as10−5from spurious electrons generated inside an analyzer can explain the peak seen at zero angle in some angular distribution measurements and the filling in of the minimum in the energy distributions in others. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148234

出版商:AIP    

年代:1997

数据来源: AIP