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Aug 1996

Volume 67, Issue 8, pp. 2671-2990

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Long‐term stabilization of the frequency and power of a laser diode

Ho Seong Lee and Sung Hoon Yang

Rev. Sci. Instrum. 67, 2671 (1996); http://dx.doi.org/10.1063/1.1147091 (4 pages) | Cited 5 times

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We report a method to stabilize the frequency of a laser diode for a long time by means of four feedback loops including a digital feedback circuit. The laser frequency was locked at a saturated absorption peak of cesium atoms. In addition, by feeding back the frequency error signal to the temperature controller of the laser diode, the power as well as the frequency was stabilized at the same time. The power stability of 0.03% was obtained, which was 260 times better than that obtained without the feedback. The frequency stabilization continued for over 1 week and the fluctuation width was about ±0.5 MHz around the locking point. © 1996 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Fiber‐optic‐bundle delivery system for high peak power laser particle image velocimetry illumination

D. J. Anderson, J. D. C. Jones, W. J. Easson, and C. A. Greated

Rev. Sci. Instrum. 67, 2675 (1996); http://dx.doi.org/10.1063/1.1147093 (5 pages) | Cited 5 times

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We demonstrate the design and implementation of a fiber‐optic‐bundle beam delivery system for particle image velocimetry (PIV) applications. The system is designed for the transmission of high peak power pulses (≳20 mJ) from a Q‐switched and frequency doubled Nd:YAG laser. A fiber bundle offers advantages over a single fiber in beam delivery systems for light sheet formation. The damage‐limit‐maximum power that can be transmitted is greater for the bundle than for any of its component fibers, and the quality of the derived light sheet is higher than that obtainable from a single large core fiber of power handling capacity equivalent to that of the bundle. The beam delivery system was demonstrated in PIV measurements on a premixed propane‐air flame. © 1996 American Institute of Physics.
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42.81.Qb Fiber waveguides, couplers, and arrays
42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
82.33.Vx Reactions in flames, combustion, and explosions

Very high Q frequency‐locked Fabry–Perot cavity

A. M. De Riva, G. Zavattini, S. Marigo, C. Rizzo, G. Ruoso, G. Carugno, R. Onofrio, S. Carusotto, M. Papa, F. Perrone, E. Polacco, G. Cantatore, F. Della Valle, P. Micossi, E. Milotti, et al.

Rev. Sci. Instrum. 67, 2680 (1996); http://dx.doi.org/10.1063/1.1147094 (5 pages) | Cited 9 times

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We report measurements on a 1.75 m long Fabry–Perot cavity locked to a Nd:YAG tunable laser using the Pound–Drever technique. The cavity decay time was measured to be about 291 μs corresponding to a quality factor Q of about 5×1011, the highest value ever reported for an optical resonant cavity. © 1996 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Improved interferometer for measuring unsteady film thickness

T. Nosoko, Y. H. Mori, and T. Nagata

Rev. Sci. Instrum. 67, 2685 (1996); http://dx.doi.org/10.1063/1.1147095 (6 pages)

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An interferometer previously developed for measuring instantaneous film thickness of the order of 10 μm–1 mm [T. Ohyama, K. Endoh, A. Mikami, and Y. H. Mori, Rev. Sci. Instrum. 59, 2018 (1988)] has been improved with respect to both facility of handling and accuracy of thickness determination. The improved version of the interferometer uses an expanded laser beam focused aslant on the subject film. The rays reflected from the front and rear surfaces of the film form interference fringes on a screen, which are then recorded in the form of a single snapshot interferogram or as a set of serial interferograms to be geometrically analyzed. Experiments with thin glass plates as sample films verified the expected advantages of the new version over the original one. The improved version of the interferometer was also tested on a liquid film asymptotically thinning as it drained down a vertical plate. The test indicated that the accuracy and precision of the new improved version far exceed those of other transient film‐thickness measuring techniques. © 1996 American Institute of Physics.
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07.60.Ly Interferometers
68.55.-a Thin film structure and morphology

Time‐domain photoacoustic measurements of absolute optical absorption coefficient using three‐chamber cell

S. V. Egerev, A. V. Fokin, and A. E. Pashin

Rev. Sci. Instrum. 67, 2691 (1996); http://dx.doi.org/10.1063/1.1147096 (7 pages) | Cited 1 time

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Pulsed photoacoustic spectroscopy (PAS) technique for immediate measuring absolute optical absorption coefficient is presented. It is based on determination of amplitude‐time characteristics of photoacoustic (PA) signal generated in air surrounding the sample under investigation. The PA signal is excited by a short laser pulse. The sample is placed in the lateral chamber of a three‐chamber PA cell. The difference of PA signals excited in two other chambers is recorded. Time dependence of PA signal for each PA cell chamber is derived. The theoretical predictions are experimentally verified. The pulsed PAS technique presented was tested experimentally by measuring water absorption coefficient at an infrared wavelength. © 1996 American Institute of Physics.
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07.64.+z Acoustic instruments and equipment
62.60.+v Acoustical properties of liquids
43.58.+z Acoustical measurements and instrumentation

Effect of coupling condition on vibration‐induced noise in fiber lead used in an optical current measurement system

W. Zhang, Y. N. Ning, A. W. Palmer, and K. T. V. Grattan

Rev. Sci. Instrum. 67, 2698 (1996); http://dx.doi.org/10.1063/1.1147097 (4 pages)

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When using a multimode fiber lead in an optical current measurement system, the optical power in the guided modes is often determined by the coupling conditions at the input end of the fiber. If only the skew rays are excited in the fiber lead—under appropriate coupling conditions—the vibration‐induced noise normally experienced in the fiber lead in such an optical current measurement system can be effectively suppressed, especially when a low coherence source and a long length of multimode fiber is used. The experimental conditions for this are considered and discussed in this article. © 1996 American Institute of Physics.
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42.81.Qb Fiber waveguides, couplers, and arrays
07.60.Vg Fiber-optic instruments

Role of the collecting resistive layer on the static characteristics of a 1D a‐Si:H thin film position sensitive detector

E. Fortunato and R. Martins

Rev. Sci. Instrum. 67, 2702 (1996); http://dx.doi.org/10.1063/1.1147098 (6 pages) | Cited 2 times

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The aim of this work is to present an analytical model able to interpret the role of the thin collecting resistive layer on the static performances exhibited by 1D amorphous silicon hydrogenated p‐i‐n thin film position sensitive detectors. The data obtained show that the devices present a linearity and a spatial resolution, of respectively, better than 99% and 20 μm for a spatial detection limit of about 80 mm, highly dependent on the characteristics exhibited by the collecting resistive layer that should have sheet resistivities in the range of 10 to 103 Ω/sq, as predicted by the model proposed. © 1996 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.60.Bt Optoelectronic device characterization, design, and modeling

A Fourier transform cavity ring down spectrometer

Richard Engeln and Gerard Meijer

Rev. Sci. Instrum. 67, 2708 (1996); http://dx.doi.org/10.1063/1.1147092 (6 pages) | Cited 35 times

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We present a pulsed multiplex absorption spectrometer in which the sensitivity of the cavity ring down absorption detection technique is combined with the multiplex advantage of a Fourier Transform spectrometer. A description of the Fourier transform cavity ring down (CRD) spectrometer—substantiated with first experimental results on the atmospheric band of molecular oxygen—is given. It is shown that as in the case of normal CRD spectroscopy, the measurement is independent of light intensity fluctuations provided the spectral intensity distribution of the light source is known and is constant during the measurement. © 1996 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
07.60.Ly Interferometers

A newly designed molecular beam Fourier transform microwave spectrometer in the range 1–4 GHz

V. Storm, H. Dreizler, D. Consalvo, J.‐U. Grabow, and I. Merke

Rev. Sci. Instrum. 67, 2714 (1996); http://dx.doi.org/10.1063/1.1147099 (6 pages) | Cited 11 times

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We report on a new design for a Fourier transform microwave spectrometer in the spectral region 1–4 GHz, specially constructed for the investigation of rotational spectra of heavy van der Waals complexes. In contrast to the commonly known molecular beam spectrometers using a Fabry–Perot resonator working with TEM00q modes, the proposed design employs a different type of resonator operating with TE01q modes. This resonator allows for compact dimensions even at cut‐off wavelengths above 0.1 m. Details of the design, performance data, and example spectra of stable molecules and complexes are given. © 1996 American Institute of Physics.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
33.20.Bx Radio-frequency and microwave spectra

Improved apparatus for picosecond pump‐and‐probe optical measurements

William S. Capinski and Humphrey J. Maris

Rev. Sci. Instrum. 67, 2720 (1996); http://dx.doi.org/10.1063/1.1147100 (7 pages) | Cited 52 times

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We present an improved method for making pump‐and‐probe optical measurements in the picosecond to nanosecond time range. In this type of measurement, a pump light pulse is used to excite the sample and the resulting changes in the optical properties are investigated by means of a probe pulse that is time‐delayed relative to the pump pulse. In most measurements of this type, a mechanical stage is used to introduce the variable time delay of the probe pulse. As a result of imperfections in the stage motion, alignment problems, and divergence of the probe beam, it has been difficult to make accurate measurements when the time delay of the probe relative to the pump is in the range above a few hundred picoseconds. To overcome these difficulties, we have developed an apparatus that utilizes a single‐mode optical fiber. In order to demonstrate the performance of this system, we present results of experiments in which the flow of heat from a thin film into a substrate has been measured. © 1996 American Institute of Physics.
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07.60.-j Optical instruments and equipment
78.47.-p Spectroscopy of solid state dynamics

The use of area detectors in Brillouin spectroscopy

D. Walton, J. J. Vanderwal, H. Xia, and P. Zhao

Rev. Sci. Instrum. 67, 2727 (1996); http://dx.doi.org/10.1063/1.1147101 (5 pages) | Cited 6 times

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The optical properties of area detectors used in conjunction with Fabry–Pérot interferometers are analyzed. A system using a charge‐coupled device as a detector for Brillouin spectroscopy is described. With a 2 pass+2 pass tandem system the finesse ranges from 50 to 63. With a collection time of about 2.5 min, the intensity of the surface Rayleigh mode and the bulk acoustic modes of Si are comparable to those obtained by scanning for many hours. © 1996 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.60.-j Optical instruments and equipment
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Fluorescence lifetime sensor of copper ions in water

D. J. S. Birch, O. J. Rolinski, and D. Hatrick

Rev. Sci. Instrum. 67, 2732 (1996); http://dx.doi.org/10.1063/1.1147090 (6 pages) | Cited 15 times

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We demonstrate an optical method for the selective detection of Cu(II) ions in water using time‐resolved fluorescence resonance energy transfer from the dye rhodamine 800 encapsulated in a sensor. In comparison to copper, quenching by other metal ions such as cobalt, nickel, and chromium is shown to be negligible. The experimental arrangement incorporates picosecond diode laser excitation and time‐correlated single‐photon counting for detection. Down to 5 mM of copper deposited on the sensor can be measured and a linear response is obtained up to at least 50 mM. A lower limit of detection for the sensor in the region of 10 ppb is shown to be readily achievable with good resolution. © 1996 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Apparatus for measuring electron‐impact excitation cross sections using fast metastable atoms produced via charge exchange

John B. Boffard, Mark E. Lagus, L. W. Anderson, and Chun C. Lin

Rev. Sci. Instrum. 67, 2738 (1996); http://dx.doi.org/10.1063/1.1147102 (14 pages) | Cited 10 times

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An apparatus for measuring absolute cross sections due to electron‐impact excitation out of the metastable levels of rare‐gas atoms via the optical method is described with the focus specifically on excitation out of the 2 3S metastable helium level. The metastable helium target (He∗) is prepared by charge exchange between 1.6 keV He+ ions and cesium vapor. An electron beam crosses the fast metastable beam target at a right angle and the fluorescence is collected at right angles to both beams. The charge transfer reaction produces He atoms mainly in the n=2 He levels. Because the target contains a negligible ground state He fraction, we can measure excitation cross sections from excitation threshold up to an arbitrarily high energy (keV regime) which represents a major improvement over previous metastable excitation cross sections measurements. The He∗ target density is extremely small (∼106 atoms/cm3) yielding minuscule signal rates. We describe steps taken to maximize the signal‐to‐noise ratio. We discuss the implications of using a fast beam target including both the finite flight time of the excited atoms across the light gathering region and the reduction of the cascade contributions to the apparent cross sections. A discussion of the identification and elimination of various systematic effects is also given. To measure absolute cross sections, we explicitly determine the spatial distributions of both the electron and metastable beams, as well as the spatially dependent response of the fluorescence gathering region. We determine the absolute flux of fast metastable atoms using a thermal detector calibrated with a He+ ion beam. As examples, we present absolute cross sections for excitation out of the 2 3S metastable level into the 3 3D and 4 3D levels. © 1996 American Institute of Physics.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Crossed‐beams arrangement for the investigation of charge‐changing collisions between multiply charged ions

S. Meuser, F. Melchert, S. Krüdener, A. Pfeiffer, K. von Diemar, and E. Salzborn

Rev. Sci. Instrum. 67, 2752 (1996); http://dx.doi.org/10.1063/1.1147103 (8 pages) | Cited 12 times

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A crossed‐beams experiment designed to study charge‐changing collisions between singly charged ions has been modified to extend its applicability to collisions between multiply charged ions in a broader range of collision energies. Computer simulations of the beam transport system and the new electrostatic analyzing units are presented. The ion‐optical predictions are tested experimentally. A data acquisition system that allows measurements of angular differential cross sections in ion–ion collisions is described. © 1996 American Institute of Physics.
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37.20.+j Atomic and molecular beam sources and techniques
34.70.+e Charge transfer

Quantitative detection of low energy positive and negative ions with a channel electron multiplier

C. A. Keller and B. H. Cooper

Rev. Sci. Instrum. 67, 2760 (1996); http://dx.doi.org/10.1063/1.1147104 (5 pages) | Cited 6 times

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We have constructed ion optics which, when interfaced with a channel electron multiplier (CEM), make possible quantitative measurements of positive and negative ion fluxes. We describe the design and operation of a detection system using these optics and present a calibration of the CEM for low energy (0.2–8.7 keV) positive and negative oxygen ions. © 1996 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
41.85.-p Beam optics

High‐current‐density gun with a LaB6 cathode

K. Ebihara and S. Hiramatsu

Rev. Sci. Instrum. 67, 2765 (1996); http://dx.doi.org/10.1063/1.1147105 (5 pages) | Cited 3 times

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To develop a high‐current electron gun for an induction linac, a prototype of a Pierce‐type electron gun using planar 12‐mm‐diam lanthanum hexaboride (LaB6) is studied as a thermionic emitter at high current densities. The cathode is heated up to temperatures of 1750 °C by electron bombardment and thermal radiation from a tungsten heater. The heater that has the highest temperature in the gun is thermally isolated from the outer vacuum chamber with heat shields. The bombardment voltage of ∼1 kV is typically applied to a gap between the cathode and the heater. The gun has been operated up to voltages of 55 kV, obtaining a maximum current density of 20 A/cm2 with a pulse width of 250 ns at a cathode temperature of 1600 °C. High‐voltage pulsing results show that the gun, with applied voltages of over 40 kV, is operated in space‐charge‐limited region at temperatures of over 1600 °C; also it is operated in a temperature‐limited region at temperatures of less than 1500 °C. An effective work function of 2.68 eV is obtained. The cathode, when heated up to 1600 °C, emits over 7 A of electrons with a ∼20% reduction after 850 h of continuous operation. These measurements were made between vacuum pressures of 10−6 and 10−7 Torr. © 1996 American Institute of Physics.
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29.25.Bx Electron sources
79.40.+z Thermionic emission

A portable time of flight system for thermal and cold neutron applications

R. E. Benenson, H. H. Chen‐Mayer, and V. Sharov

Rev. Sci. Instrum. 67, 2770 (1996); http://dx.doi.org/10.1063/1.1147106 (5 pages)

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A very small Fermi‐type neutron chopper fashioned by cutting slots in a boron nitride cylinder was developed for use with a source of thermal and cold (subthermal velocity) neutrons. The original goal was to characterize spectra emerging from glass capillary fibers of less than 1 mm diameter, but other applications became apparent. For approximately 1 m flight paths, conventional nuclear electronics had to be adapted to the millisecond flight times. Both time‐to‐amplitude converter and multiscaling time‐data storage methods were used. Data corrections for the particular geometry are reviewed and applied to the present geometry. Among examples of its potential use, the spectrum of a newly installed cold source was measured. © 1996 American Institute of Physics.
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29.30.Hs Neutron spectroscopy
07.05.Kf Data analysis: algorithms and implementation; data management

Digital image processing of images obtained with a Pu–Be (∼107) neutron source

C. G. Panchal, A. Sinha, B. D. Bhawe, A. Shyam, M. Srinivasan, and V. M. Joshi

Rev. Sci. Instrum. 67, 2775 (1996); http://dx.doi.org/10.1063/1.1147107 (5 pages) | Cited 2 times

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A Nuclear particle scintillation imaging system, developed earlier by the authors, has been upgraded and tested for its radiographic performance using a low intensity Pu–Be (∼107 n/s) source. The main objective of this work was to check the feasibility of a neutron radiography facility using a low intensity Pu–Be isotopic source and evaluate its performance. To accumulate the neutron exposure, an on‐line frame integration method was used for imaging static objects. Because integrated images from the system were mottled and poor in contrast, a video image processing system was employed to enhance the quality of the integrated images. Significant improvements in image quality are seen, when image processing techniques such as smoothing, contrast stretching, edge enhancement, and histogram equalization are employed. This article provides an overview of the improvement in the image quality consequent to implementation of image processing techniques. © 1996 American Institute of Physics.
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07.05.Pj Image processing
81.70.-q Methods of materials testing and analysis

Scintillating fiber hodoscope for a bremsstrahlung luminosity monitor at an electron–positron collider

D. H. Brown, D. H. Orlov, G. S. Varner, W. A. Worstell, and S. I. Redin

Rev. Sci. Instrum. 67, 2780 (1996); http://dx.doi.org/10.1063/1.1147108 (8 pages)

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The performance of a scintillating fiber (2 mm diameter) position sensitive detector (4.8×4.8 cm2 active area) for the single bremsstrahlung luminosity monitor at the VEPP‐2M electron‐positron collider in Novosibirsk, Russia is described. Custom electronics is triggered by coincident hits in the Y and Y planes of 24 fibers each, and reduces 64 photomultiplier signals to a 10‐bit (X,Y) address. Hits are accumulated (10 kHz) in memory and display (few Hz) the VEPP‐2M collision vertex. Fitting the strongly peaked distribution (∼3–4 mm at 1.6 m from the collision vertex of VEPP‐2M) to the expected QED angular distribution yields a background in agreement with an independent determination of the VEPP‐2M luminosity. © 1996 American Institute of Physics.
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29.40.Wk Solid-state detectors
29.20.db Storage rings and colliders

A scanning Auger electron spectrometer for internal surface analysis of Large Electron Positron 2 superconducting radio‐frequency cavities

C. Benvenuti, R. Cosso, J. Genest, M. Hauer, D. Lacarrère, A. Rijllart, and R. Saban

Rev. Sci. Instrum. 67, 2788 (1996); http://dx.doi.org/10.1063/1.1147109 (8 pages)

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A computer‐controlled surface analysis instrument, incorporating static Auger electron spectroscopy, scanning Auger mapping, and secondary electron imaging, has been designed and built at CERN to study and characterize the inner surface of superconducting radio‐frequency cavities to be installed in the Large Electron Positron collider. A detailed description of the instrument, including the analytical head, the control system, and the vacuum system is presented. Some recent results obtained from the cavities provide examples of the instrument’s capabilities. © 1996 American Institute of Physics.
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29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy
29.20.db Storage rings and colliders

Design studies on a vacuum bellows assembly with radio frequency shield for the KEK B factory

Y. Suetsugu, K. Ohshima, and K. Kanazawa

Rev. Sci. Instrum. 67, 2796 (1996); http://dx.doi.org/10.1063/1.1147110 (16 pages) | Cited 10 times

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A bellows assembly with a radio frequency (rf) shield has been designed and developed for the KEK B factory (KEKB). The rf shield is the usual finger type but has a special spring finger to press contact fingers onto the beam tube. A test of the mechanical performance using a trial model shows good results. Further experimental studies are focused on the two key points of the finger‐type rf shield, that is, the contact force of fingers and the length of slits between adjacent fingers. First, to reduce the excess abrasion at contact points, the necessary contact force is studied experimentally utilizing microwaves. Abnormal heating is checked by transmitting a 508 MHz cw microwave through a trial model in a coaxial line. Arcing at the contact point in vacuum is observed by transmitting a 2856 MHz pulse microwave in a rectangular waveguide equipped with a model piece of the rf shield. A contact force of 50 g/finger is found to be necessary. Second, the optimum slit length is studied with a strategy to minimize the higher order mode (HOM) power leaked from the beam tube into the inside of the bellows while keeping a sufficient sliding stroke. The coupling coefficient, β, of the rf shield is measured experimentally from the Q value of a TE mode resonance in a cylindrical cavity connected to the bellows assembly. Using the measured dependence of β on the slit length, a rough estimation of leaked HOM power is tried for the KEKB. The expected leaked power is about 6–18 W for a slit length of 20 mm, which is in the allowable range. The results obtained through these experiments are reflected to the design for the KEKB: the contact force of 80–100 g/finger will be adopted finally considering the manufacturing error of typically ±10 g/finger in our test and leaving a margin for higher frequencies. The nominal slit length will be set to be 20 mm, keeping the expansion/contraction of ±10 mm. © 1996 American Institute of Physics.
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07.30.Kf Vacuum chambers, auxiliary apparatus, and materials
29.20.-c Accelerators

Single beam laser induced fluorescence technique for plasma transport measurements

D. A. Edrich, R. McWilliams, and N. S. Wolf

Rev. Sci. Instrum. 67, 2812 (1996); http://dx.doi.org/10.1063/1.1147111 (6 pages) | Cited 10 times

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A technique for measuring ion transport using laser‐induced fluorescence has been developed and tested in an argon plasma. It uses only one broadband beam thus being simpler than some previous techniques because no detection beam is required. First, a 5 μs laser pulse centered on 611 nm stimulates a transition from the metastable state in Ar(II) 3d 2G9/2 to 4p 2F7/20. A 4p 2F7/20 to 4s2D5/2transition rapidly results with emission at 461 nm. Upon cessation of the laser pulse, the 461 nm light in the detection volume does not return to its background level immediately because the 3d 2G9/2 level is partially depleted. The time history of the 461 nm signal in returning to steady‐state background intensity provides a means of determining ion transport because the recovery signal is due to processes including ion excitation, diffusion, convection, and thermal motion. Measurements of the ion velocity distribution yield the contributions of thermal and convective effects to ion transport. By varying the laser beam diameter and the detection volume the plasma ion spatial diffusion coefficient D, and the time, τp it takes for processes other than transport to bring the 461 nm emission back to the steady‐state background level are determined. For example, in one set of plasma conditions D=0.58±0.16 m2/s and τp=59±7 μs were found. © 1996 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties

Retarding field energy analyzer for the characterization of negative glow sheet plasmas in a magnetic field

J. Mathew, R. A. Meger, R. F. Fernsler, and J. A. Gregor

Rev. Sci. Instrum. 67, 2818 (1996); http://dx.doi.org/10.1063/1.1147088 (8 pages) | Cited 4 times

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A retarding field energy analyzer has been developed for diagnosing 300 μs duration, 60 cm×60 cm negative glow, sheet plasmas immersed in a 150–250 G axial magnetic field. The electron density in these 4.5 kV, 13 A, 120 mTorr discharges in air and other gases, is high enough to reflect X‐band microwaves. The presence of the magnetic field makes the suppression of secondary electrons from the Faraday collector surface more difficult. The approach taken here is to bias the entire collection circuit and the amplifiers 90 V positive with respect to the data acquisition room. The differentially pumped analyzer is designed to accept electrons with a large range of perpendicular velocities, and it measures the parallel velocity distribution function of the discharge electrons entering a 0.64‐mm‐diam hole in the anode plate. It gives valuable information about the energy spectrum of the energetic beam electrons emitted from the cathode, and the effect of energy loss and scattering processes on this propagating beam component. Additionally, since the analyzer sampling hole is offset from the anode‐cathode axis, the current density profile can be measured for different bias voltages on the retarding grid, by rotating the linear cathode about the vertical anode‐cathode axis. These profiles give the sheet thickness for the beam and plasma components of the negative glow discharge. It also gives useful information about the scattering induced beam spreading and its effects on the plasma sheet thickness and electron density. © 1996 American Institute of Physics.
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52.70.Nc Particle measurements
52.80.Hc Glow; corona

Investigations on calibration sources for soft‐x‐ray plasma spectroscopy and impurity monitors

U. Schumacher, K. Asmussen, G. Fussmann, T. Liebsch, and R. Neu

Rev. Sci. Instrum. 67, 2826 (1996); http://dx.doi.org/10.1063/1.1147112 (5 pages) | Cited 1 time

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For absolute soft‐x‐ray line intensity measurements to deduce elemental concentrations and parameters of magnetically confined plasmas large‐area x‐ray sources are developed and investigated. These calibration sources use K, L, and M transitions in different elements and cover a wide photon energy (and wavelength) range. From the measured absolute line intensities of these sources the quantum efficiency values of numerous elements for K‐, L‐, and M‐line emission per incident electron are deduced. They represent the basis of simple soft‐x‐ray monitors for impurities in fusion plasmas. © 1996 American Institute of Physics.
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52.70.La X-ray and γ-ray measurements
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Novel technique for investigating the temperature effect on the diffusion coefficient of naphthalene into air

Ping‐Hei Chen, Jr‐Ming Miao, and Ching‐Sung Jian

Rev. Sci. Instrum. 67, 2831 (1996); http://dx.doi.org/10.1063/1.1147113 (6 pages) | Cited 1 time

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This article describes a technique that uses a piezoelectric quartz crystal microbalance (QCM) for determining the diffusion coefficient of naphthalene into air. The QCM is placed onto the open top of a closed Stefan tube and its active surface is covered with a thin layer of solid naphthalene. Due to the markedly enhanced QCM resolution of 10−9 g/cm2 over that of the conventional digital electronic balance, the QCM in this study requires much less time than previous studies using digital electronic balances for measuring the diffusion coefficient in a binary gas system. At P=0.1013 MPa and in a temperature range from 278.25 to 315.15 K, the empirical correlations to evaluate both the diffusion coefficient of naphthalene into air at 1 atm pressure and the Schmidt number of naphthalene at various temperatures are presented. The measurement uncertainty of the diffusion coefficient of naphthalene into air with the present system is less than 3%. In addition, measured results verify that the measurement of the diffusion coefficient of naphthalene into air is only slightly affected by the length of the diffusion tube if the QCM is used in the closed Stefan tube for measuring the mass flux in the diffusion tube. © 1996 American Institute of Physics.
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51.20.+d Viscosity, diffusion, and thermal conductivity
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