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Dec 1990

Volume 61, Issue 12, pp. 3653-3927

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Laser‐based microchemical analysis

Norman J. Dovichi

Rev. Sci. Instrum. 61, 3653 (1990); http://dx.doi.org/10.1063/1.1141533 (16 pages) | Cited 10 times

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Microchemical analysis is the determination of the chemical composition of small volume samples, typically smaller than 1 mm3. The spatial coherence of the laser has been exploited by workers in many fields to probe these small volume samples. This review considers three classes of microchemical analyses: detectors for microscale separations, spectroscopic studies of minute volume samples, and laser‐based microscopy. In the first case, high‐sensitivity laser‐based detectors are coupled with high‐efficiency separation techniques to produce powerful analytical tools for submicroliter volume samples. In the second case, highly selective measurements are made on small volume samples through use of either immunological reagents or spectroscopically rich techniques. In the third case, high spatial resolution images of solid samples are created by recording a spectroscopic signal as a sample is moved with respect to a tightly focused laser beam. In each case, measurements with uniquely high sensitivity, selectivity, and spatial resolution are made possible by use of a laser beam.
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82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
42.60.By Design of specific laser systems

Photon scanning tunneling microscopy

R. C. Reddick, R. J. Warmack, D. W. Chilcott, S. L. Sharp, and T. L. Ferrell

Rev. Sci. Instrum. 61, 3669 (1990); http://dx.doi.org/10.1063/1.1141534 (9 pages) | Cited 57 times

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An optical tunneling microscope is presented that operates in exactly the same way as the electron scanning tunneling microscope (ESTM). It takes advantage of evanescent fields generated by the total internal reflection (TIR) of light at the interface between materials of different optical densities. The photon scanning tunneling microscope (PSTM) employs an optically conducting probe tip to map spatial variations in the evanescent and scattered field intensity distributions adjacent to a sample surface, which forms or is placed on the TIR surface. These variations are due to the local topography, morphology, and optical activity of the surface and form the basis of imaging. Evanescent field theory is discussed and the evanescent field intensity as a function of surface‐probe separation is calculated using several probe tip models. After a description of PSTM construction and operation, evanescent field intensity measurements are shown to agree with the model calculations. PSTM images of various sample surfaces demonstrate subwavelength resolution exceeding that of conventional optical microscopy, especially in the vertical dimension. Limitations and interpretation of PSTM images are discussed as well as the PSTMs applicability to other forms of surface analysis.
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07.60.Pb Conventional optical microscopes
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

New cross‐beam technique for charge transfer cross section measurement using a pulsed ion beam produced by laser photoionization

Shuji Sakabe, Yasukazu Izawa, Masaki Hashida, Toshihiro Naka, Tomokazu Sudo, Takayasu Mochizuki, Tatsuhiko Yamanaka, Sadao Nakai, and Chiyoe Yamanaka

Rev. Sci. Instrum. 61, 3678 (1990); http://dx.doi.org/10.1063/1.1141535 (8 pages) | Cited 7 times

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A new cross‐beam technique has been developed to measure the charge transfer cross sections of metallic atoms which have not been experimentally investigated previously. Two high‐density atomic beams were produced by the vaporization of a metal heated with an electron beam gun. A pulsed ion beam produced from one atomic beam by laser photoionization was collided with another atomic beam. By colliding the pulsed ion beam produced in this manner with the second atomic beam, the apparatus was simplified in comparison with conventional one; additionally, only a single pulsed laser shot is required to obtain the data necessary to determine a cross section. By using repetitive laser pulses it is possible to acquire in a short time a more accurate cross section as a function of impact energy. The apparatus was successfully applied to the measurement of the charge transfer cross section of gadolinium, a metallic atom with a relatively high ionization potential and high melting point.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
34.70.+e Charge transfer

Direct injection supersonic cluster beam source for FT‐ICR studies of clusters

Shigeo Maruyama, Lila R. Anderson, and Richard E. Smalley

Rev. Sci. Instrum. 61, 3686 (1990); http://dx.doi.org/10.1063/1.1141536 (8 pages) | Cited 99 times

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A miniaturized pulsed supersonic beam source has been developed using laser vaporization of a computer‐controlled target disk, producing intense beams of cluster ions with excellent repeatability and control. Due to its small size and narrow pulse width, the entire source is adequately pumped by a single 170 l /s turbopump. The resultant vacuum quality permits this source to be attached to a Fourier transform ion cyclotron resonance apparatus (FT‐ICR) such that the supersonic cluster ion beam is directly injected. The result is a powerful but simple FT‐ICR instrument of wide applicability. The new source is suited as well for a variety of other uses such as molecular beam epitaxy.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.50.Gj Plasma heating by particle beams

An automatic molecular beam microwave Fourier transform spectrometer

U. Andresen, H. Dreizler, J.‐U. Grabow, and W. Stahl

Rev. Sci. Instrum. 61, 3694 (1990); http://dx.doi.org/10.1063/1.1141537 (6 pages) | Cited 52 times

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We present hardware and software details of the pulsed molecular beam microwave Fourier transform (MB‐MWFT) spectrometer used in the Kiel microwave group. We emphasize an automatic scanning facility which greatly increases the efficiency of MB‐MWFT spectroscopy for the measurement of unassigned spectra.
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42.30.Kq Fourier optics

An FT‐IR based instrument for measuring spectral emittance of material at high temperature

J. R. Markham, P. R. Solomon, and P. E. Best

Rev. Sci. Instrum. 61, 3700 (1990); http://dx.doi.org/10.1063/1.1141538 (9 pages) | Cited 15 times

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For surfaces at high temperature the emitted spectrum of electromagnetic radiation is the most convenient probe of temperature, if the spectral emittance (emissivity) of the sample at that temperature is known. A bench top instrument has been developed that, when coupled to a Fourier transform infrared (FT‐IR) spectrometer, allows for the measurements of emission, directional‐hemispherical reflection, and directional‐hemispherical transmission from materials at elevated temperatures. From these radiative property measurements, the temperature at the measurement point and the spectral emittance of the surface can both be obtained. The method has been applied to a variety of materials (i.e., metals, dielectrics, coal slags) with a variety of surface properties (i.e., partially transmitting and nontransmitting; specularly reflecting and diffusely reflecting) at temperatures up to 2226 K. The article describes the technique, presents the results for several materials, and compares results with those for other investigators.
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07.20.Dt Thermometers
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.30.Kq Fourier optics
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

A high‐throughput Raman notch filter set

G. J. Puppels, A. Huizinga, H. W. Krabbe, H. A. de Boer, G. Gijsbers, and F. F. M. de Mul

Rev. Sci. Instrum. 61, 3709 (1990); http://dx.doi.org/10.1063/1.1141963 (4 pages) | Cited 6 times

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A chevron‐type Raman notch filter (RNF) set is described. lt combines a high signal throughput (up to 90% around 1600 cm−1 and ≳80% between and 700 and 2700 cm−1) with a laser line suppression of 108–109. The filter set can be used to replace the first two dispersion stages in triple‐stage Raman monochromators commonly employed in multichannel detection systems. This yields a gain in intensity of the detected Raman signal of a factor of 4. It is shown that in Raman spectrometers with a backscatter geometry, the filter set can also be used to optically couple the microscope and the spectrometer. This leads to a further increase in signal intensity of a factor of 3–4 as compared to the situation where a beam splitter is used. Additional advantages of the RNF set are the fact that signal throughput is almost polarization independent over a large spectral interval and that it offers the possibility to simultaneously record Stokes and anti‐Stokes spectra.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers
78.30.-j Infrared and Raman spectra
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Parametric optimization of an easily constructed pulsed xenon‐ion laser

C. M. Dai, K. H. Wu, W. F. Hsieh, and D. S. Chuu

Rev. Sci. Instrum. 61, 3713 (1990); http://dx.doi.org/10.1063/1.1141539 (3 pages) | Cited 5 times

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An easily fabricated xenon‐IV ion laser is described. The various parameters considered are the gas pressures, the excitation voltages, and the repetition rates. Based on our results we believe that there exists an optimal excitation voltage and an optimal repetition rate for achieving largest lasing power and good reliability.
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42.60.By Design of specific laser systems

A phototube constant current circuit design used in phase modulated spectroscopic ellipsometry

Koorosh Vasseghi, Kintak Yue, and Julio R. Blanco

Rev. Sci. Instrum. 61, 3716 (1990); http://dx.doi.org/10.1063/1.1141540 (3 pages)

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A simple differential integrator circuit is described for use with a Kepco OPS 1000B high‐voltage power supply. The circuit maintains a constant phototube output dc current as incident light changes intensity during a spectroscopic measurement. The dc level is maintained better than ± 50 μV. The response time constant of the circuit is 1.6 ms, thus attenuating noise components as high as 0.6 kHz. However, the circuit is insensitive to the high‐frequency signal components (50 and 100 kHz) normally measured in phase modulated spectroscopic ellipsometry. This circuit design can be used as explained with most phototubes without any changes. The high‐voltage bias is easily computer controlled.
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07.50.-e Electrical and electronic instruments and components
84.30.Jc Power electronics; power supply circuits
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers

Development of a frequency‐stabilized compact light source for an optically pumped Cs frequency standard

Takeshi Ikegami, Shin‐Ichi Ohshima, Yasuhiro Nakadan, and Yasuki Koga

Rev. Sci. Instrum. 61, 3719 (1990); http://dx.doi.org/10.1063/1.1141541 (3 pages) | Cited 2 times

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A compact light source using a laser diode, whose frequency was stabilized to a saturated absorption spectrum of the Cs‐D2 line (λ=852 nm), was developed for use of an optically pumped cesium frequency standard. The temperature of the laser diode was stabilized within 0.1 mK by two stages of feedback systems. Frequency stabilization to the saturated absorption spectrum was performed by modulating the injection current to the laser diode with 100 kHz. The frequency stability was measured by taking the beat of two light sources thus stabilized, and it was estimated to be 4.4×10−11(15 kHz) at an averaging time of 600 ms.
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07.60.-j Optical instruments and equipment
06.30.Ft Time and frequency
06.20.F- Units and standards

An automatic focus/hold system for optical microscopes

Edward H. Hellen and Daniel Axelrod

Rev. Sci. Instrum. 61, 3722 (1990); http://dx.doi.org/10.1063/1.1141542 (4 pages) | Cited 5 times

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A system for maintaining long‐term focus of samples under high‐magnification quantitative observation in an epi‐illumination optical microscope is described. A negative feedback signal is generated from focus‐dependent changes in the backreflection of an off‐axis HeNe laser. This reflection is intercepted by a small prism downbeam from the standard trinocular head, and detected by a small two‐photodiode array. Spontaneous drifts in sample focus (presumably due to thermal and mechanical relaxations) are detected as a nonzero difference signal, which is used to drive a dc motor mechanically coupled to the fine‐focus knob of the microscope. This system has several advantages: (1) it is completely compatible and nonobstrusive with concurrent data acquisition of sample intensities; (2) it requires no alteration of the sample, sample stage, or objective; (3) it monitors the focal position of sample areas very near to those under observation; (4) it is inexpensive. In an experimental test, the system can hold a thin glass coverslip sample (a common substrate for biological cell cultures) to within 0.5 μm of its preset focus position, well within the depth of focus of the microscope. Without the system, such samples typically drift several micrometers over periods of 10 min. In response to a disturbance of the focus knob, the system can restore the focus to within 0.5 μm of the preset position.
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07.60.Pb Conventional optical microscopes
42.15.Eq Optical system design
87.80.-y Biophysical techniques (research methods)

An ‘‘on’’‐gated photomultiplier circuit for the determination of phosphorescence lifetimes

Mark C. Piton, Wolfgang Panning, and Mitchell A. Winnik

Rev. Sci. Instrum. 61, 3726 (1990); http://dx.doi.org/10.1063/1.1141543 (3 pages) | Cited 5 times

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An ‘‘on’’‐gated photomultiplier circuit is described which possesses a cutoff ratio >103 by switching dynodes 1 and 3 of a nine‐stage side‐on phototube (Hamamatsu models 1P28, R955, etc.). ‘‘On’’‐gate delay and gate‐width times are continuously variable between 150 ns and 10 ms. The ‘‘ringing’’ usually observed after the gate opening in similar circuit designs, due to the propagation delay in the dynode chain and the capacitive coupling between the anode and the switched dynodes, has been greatly reduced using a ‘‘spike compensator’’ circuit. When −1000 V was applied to the anode of the phototube, the resulting output of the circuit was linear 80 ns after the unit was triggered. The circuit will also operate as an ungated photomultiplier.
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29.40.Mc Scintillation detectors
07.90.+c Other topics in instruments, apparatus, and components common to several branches of physics and astronomy (restricted to new topics in section 07)

Remote photoacoustic measurements in aqueous solutions using an optical fiber

R. E. Russo, D. Rojas, P. Robouch, and R. J. Silva

Rev. Sci. Instrum. 61, 3729 (1990); http://dx.doi.org/10.1063/1.1141544 (4 pages) | Cited 8 times

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A photoacoustic spectrometer was developed for remote optical absorption measurements in aqueous solutions using an 85‐m optical fiber to deliver pulsed tunable dye laser radiation to a sample cuvette located in a glove box. The spectrometer was tested using aqueous solutions of praseodymium ions. Beer’s law was verified down to a concentration of 8×10−6M for an equivalent absorptance of 3.2×10−5 cm−1.
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43.58.+z Acoustical measurements and instrumentation
42.81.Qb Fiber waveguides, couplers, and arrays
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

An Auger photoelectron coincidence spectrometer

S. Thurgate, B. Todd, B. Lohmann, and A. Stelbovics

Rev. Sci. Instrum. 61, 3733 (1990); http://dx.doi.org/10.1063/1.1141545 (5 pages) | Cited 13 times

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The feasibility of photoelectron Auger electron coincidence spectroscopy from solid surfaces has been demonstrated by Haak et al. [Ph. D. thesis, University of Groningen, The Netherlands, 1983; Phys. Rev. Lett. 41, 1825 (1978); Rev. Sci. Instrum. 55, 696 (1984)]. They were able to show the considerable power of the technique in deconvoluting the L23M45M45 line of Cu by finding those parts of the line that were due to a 2p3/2 hole and those which were due to a 2p1/2 hole. However, the technique is a difficult one, requiring two analyzers rather than one and complex coincidence electronics. Even then a single spectrum can take weeks to acquire. This initial work was followed up by Jensen et al. [Phys. Rev. Lett. 62, 71 (1989); Physical Electronics Conference abstract A‐5, July, 1988] using a synchrotron to provide the radiation and a means of getting very good timing resolution. They were able to acquire Cu spectra in 2–3 days using this system. We have constructed a set of electron analyzers specifically for this experiment. We used the ideas of Völkel and Sandner [J. Phys. E 16, 456 (1983)] to produce analyzers that have good angular acceptance, good energy resolution, and very good timing resolution. With this system we are able to measure coincidence line shapes, for elements with large enough cross section, within a few days using a standard laboratory dc x‐ray source.
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07.90.+c Other topics in instruments, apparatus, and components common to several branches of physics and astronomy (restricted to new topics in section 07)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Line focus of an elliptic cone for an x‐ray crystal spectrograph

D. W. Phillion and B. A. Hammel

Rev. Sci. Instrum. 61, 3738 (1990); http://dx.doi.org/10.1063/1.1141546 (7 pages) | Cited 4 times

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The crystal in any flat crystal x‐ray spectrograph with the film plane at any angle and any position may be bent sagittally into an elliptic conical shape such that a perfect line focus is formed on the film plane for a point source at a fixed location. However, for high spectral resolution, only a narrow strip along the cone can be utilized. This strip will be near the plane formed by the axis of the cone and the source point. The elliptic cone has mirror symmetry in this plane. The equation of this cone is determined and its properties are discussed. Any conical surface has zero intrinsic curvature since one of the two principal radii of curvature is zero, so it is no more difficult to bend a crystal to this shape than to a concave circular cylinder with the same principal radius of curvature.
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07.85.-m X- and γ-ray instruments
61.05.C- X-ray diffraction and scattering

A miniature electron‐beam evaporator for an ultrahigh‐vacuum atom‐probe field‐ion microscope

X. W. Lin, J. G. Hu, D. N. Seidman, and H. Morikawa

Rev. Sci. Instrum. 61, 3745 (1990); http://dx.doi.org/10.1063/1.1141547 (5 pages) | Cited 2 times

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A miniature electron‐beam evaporator (MEBE) has been fabricated and adapted to our ultrahigh‐vacuum atom‐probe field‐ion microscope (APFIM). The MEBE allows for in situ vapor deposition−under ultrahigh‐vacuum conditions ( < 4 × 10−10 Torr)−of a wide range of elements, on the surface of an atomically clean FIM specimen; the surface is prepared via the field‐evaporation process. The deposition rate of an evaporant from the MEBE is calibrated to give an accurate value of this quantity. Examples of the deposition−at ≊0.3 nm min−1− of silicon or titanium on tungsten FIM specimens are presented. And in the case of a Ti/W couple it is demonstrated that an interface between a tungsten substrate and a titanium overlayer is chemically sharp on an atomic scale; the titanium was vapor deposited at a substrate temperature of 77 K. Also a 20‐kV electron‐beam gun was adapted to our APFIM. This gun is useful for in situ electron‐beam heating of bilayer couples, or the introduction of point defects in metal oxide or semiconductor overlayers via electronic mechanisms.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.37.Vj Field emission and field-ion microscopy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Low accelerating voltage SEM imaging and metrology using backscattered electrons

Michael T. Postek

Rev. Sci. Instrum. 61, 3750 (1990); http://dx.doi.org/10.1063/1.1141548 (5 pages) | Cited 8 times

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An approach to measure semiconductor structures for nondestructive submicrometer metrology in the scanning electron microscope (SEM) at low accelerating voltage is described utilizing the collection and measurement of only the backscattered electron signal rather than the more commonly used secondary electron signal. In this technique, the backscattered electron signal is collected using a high‐efficiency microchannel‐plate electron detector system with the front face of the detector biased negatively to reject the low‐energy secondary electrons thus collecting only the backscattered electrons. The advantage of using the backscattered electron signal is discussed, as well as a comparison to measurements using the secondary electron signal. The potential of this technique for application to accurate SEM metrology and standards development is also discussed.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.20.F- Units and standards
85.40.Hp Lithography, masks and pattern transfer

High resolution time‐of‐flight positron emission tomograph

Keizo Ishii, Hikonojo Orihara, Taiju Matsuzawa, David M. Binkley, and Ronald Nutt

Rev. Sci. Instrum. 61, 3755 (1990); http://dx.doi.org/10.1063/1.1141549 (8 pages) | Cited 4 times

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A time‐of‐flight positron emission tomograph (TOF‐PET) was recently developed for the purpose of clinical medical study and brain research. It provides high‐quality positron images with a spatial resolution of 8 mm full width at half‐maximum (FWHM) which is obtained by the use of time‐of‐flight (TOF) location techniques and small 10×18‐mm BaF2 detectors to detect the positron‐electron annihilation γ‐rays. The time‐of‐flight resolving time was 623 ps (FWHM) in the system, which has improved the S/N ratio for positron images. This new TOF‐PET has been designed to digitally record the arriving time of γ‐rays at the detectors using the system clock. With this method, the architecture of hard and software for taking TOF sinograms and reconstructing TOF images is simplified compared to that of other TOF‐PET systems. The details of this system are described here.
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87.57.U- Nuclear medicine imaging

The scanning tunneling microscope as a high‐gain, low‐noise displacement sensor

Mark F. Bocko

Rev. Sci. Instrum. 61, 3763 (1990); http://dx.doi.org/10.1063/1.1141550 (6 pages) | Cited 11 times

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We consider the capabilities of the tunneling probe of the scanning tunneling microscope as a displacement sensor as distinguished from its better established application to surface imaging. Electromechanical transducers that operate on this principle can achieve very large gain and a noise temperature equal to the minimum required by quantum mechanics for any linear amplifier. We present a two‐port network representation of the tunneling transducer, including noise, that allows us to discuss the differences between the tunneling transducer and more conventional electromechanical transducers and to draw analogies between a tunneling transducer and a transistor. We present a simple equivalent circuit for the tunneling transducer including two uncorrelated noise generators, the tunneling current shot noise and the fluctuating force that the tunneling probe exerts on a test mass. In practice the fluctuating ‘‘back action’’ force spectral density is exceedingly small. We give an example of a system in which a tunneling transducer is used to monitor the motion of a very small mechanical harmonic oscillator. A transducer gain of approximately 108 should be achieved in this system that makes negligible the noise contribution of conventional following electronics. The contribution to the noise of the tunneling transducer itself should be near the quantum limit and the most significant remaining source of noise is the mechanical oscillator’s Brownian motion. The tunneling transducer represents a new approach for measuring mechanical displacements and may profoundly influence transducer technology in applications from gravity wave detectors down to measurements on single molecules.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

An ultrahigh vacuum scanning tunneling microscope for surface science studies

D. M. Zeglinski, D. F. Ogletree, T. P. Beebe, R. Q. Hwang, G. A. Somorjai, and M. B. Salmeron

Rev. Sci. Instrum. 61, 3769 (1990); http://dx.doi.org/10.1063/1.1141551 (6 pages) | Cited 37 times

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We describe the construction and operation of a scanning tunneling microscope designed in our laboratory that fits standard ultrahigh vacuum (UHV) systems as an add‐on instrument. Sample motion is accomplished by electrical signals, eliminating mechanical feedthroughs. Samples are easily transferred to a modified Varian manipulator for heating and interfacing with other surface science techniques. In situ tip replacement and sample transfer in and out of the UHV system is also possible.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Performance of a high‐current metal vapor vacuum arc ion source

Hiroshi Shiraishi and Ian G. Brown

Rev. Sci. Instrum. 61, 3775 (1990); http://dx.doi.org/10.1063/1.1141552 (8 pages) | Cited 6 times

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The operational characteristics of a metal vapor vacuum arc ion source have been studied. The beam current has been measured as a function of ion source extraction voltage (5–80 kV), arc current (50–250 A), metal‐ion species (Ti, Ta, and Pb), and extractor grid spacing (0.89 and 0.38 cm). The measured beam current ranged up to 700 mA. The parametric variation of beam current is compared to that expected from the Child–Langmuir equation and excellent agreement is found.
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52.80.Vp Discharge in vacuum
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Using the second harmonic from a Nd:YAG as a probe beam for determination of free electron density in a plasma induced by the fundamental

Thad J. Englert and Mostafa A. Beik

Rev. Sci. Instrum. 61, 3783 (1990); http://dx.doi.org/10.1063/1.1141553 (4 pages) | Cited 1 time

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The higher harmonics are typically generated in Nd:YAG lasers equipped with standard harmonic generator crystals and these harmonics become useful as probe beams of light in applications where optical measurements are required during early stages of laser‐induced effects. The system described here makes use of a spatially filtered second harmonic beam for schlieren photography of a plasma created by the fundamental beam of a Nd:YAG laser interacting with a gas. Fringe patterns recorded on schlieren photographs of the plasma region provide measurements of the variation in the index of refraction which in turn yield the variation in electron density within the plasma.
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52.70.Nc Particle measurements
52.38.-r Laser-plasma interactions

Numerical study of neutral beam probe spectroscopy for edge fluctuation measurements

A. Komori, S. Nagai, T. Morisaki, and Y. Kawai

Rev. Sci. Instrum. 61, 3787 (1990); http://dx.doi.org/10.1063/1.1141554 (6 pages) | Cited 4 times

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A thermal neutral beam probing combined with a spectroscopic technique is numerically demonstrated to be available to the measurement of local electron‐density fluctuations in edge plasmas, although the spatial attenuation of the beam due to the electron‐impact ionization is not negligible. It is found that the fluctuations are accurately measured in the region where the density is lower than (4–6) × 1012 cm−3, and that this critical density decreases slightly for the fluctuations which propagate in the beam direction with phase velocities comparable to a thermal speed of the beam. Some results of the beam probe mounted on the TEXTOR tokamak are also described and good agreement is found between numerical and experimental results.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.-m Plasma diagnostic techniques and instrumentation
52.25.Gj Fluctuation and chaos phenomena

Visible spectroscopy on the Tokamak de Varennes with high spatial resolution

D. Lafrance, A. Boileau, B. L. Stansfield, and W. Zuzak

Rev. Sci. Instrum. 61, 3793 (1990); http://dx.doi.org/10.1063/1.1141555 (4 pages) | Cited 5 times

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A vertical slice of a tokamak plasma is imaged onto the entrance slit of a spectrometer, giving at the exit plane both the spectral (horizontal axis) and the spatial (vertical axis) distributions of the collected light. An intensified CID (charge injection device) camera is mounted at the exit plane to record the spatially and spectrally resolved emission profiles of low‐Z impurities, with a temporal resolution of 1/60 s. The large number of lines of sight allows for inversion of chord‐integrated signals to obtain local emissivities. Profiles from several ionization stages of carbon and oxygen are compared to the predictions of the impurity transport code MIST (multi‐ionized species transport) to deduce impurity diffusion coefficients.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Time‐resolved temperature measurement of a pinched plasma using the dispersive x‐ray analysis of the continuum emission

F. Venneri and G. Gerdin

Rev. Sci. Instrum. 61, 3797 (1990); http://dx.doi.org/10.1063/1.1141504 (10 pages)

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The dispersive analysis of the x‐ray continuum is employed to determine the electron temperature of a dense pinched plasma. A curved crystal spectrometer was used to obtain the desired dispersion, and two or more p‐i‐n (doubly diffused silicon) diodes were used to monitor the time‐resolved emission. The dispersive technique is inherently more accurate than filtering techniques and simpler to implement than laser scattering techniques. In an experimental verification of the technique, the time‐resolved temperature of a plasma focus pinch was measured under various conditions, and was found to be consistent with density observations and MHD calculations. It was possible to observe the cooling effect of radiation emission from seeded plasma focus discharges. The elliptical crystal spectrometer is shown to be well suited to the analysis of the x‐ray emission from a pinched plasma source.
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52.70.La X-ray and γ-ray measurements
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