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Mar 1994

Volume 65, Issue 3, pp. 533-764

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Magnetic manipulation instrumentation for medical physics research

G. T. Gillies, R. C. Ritter, W. C. Broaddus, M. S. Grady, M. A. Howard, and R. G. McNeil

Rev. Sci. Instrum. 65, 533 (1994); http://dx.doi.org/10.1063/1.1145242 (30 pages) | Cited 32 times

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The noncontact magnetic manipulation of probe masses within the body is an area of research that has received substantial attention from the medical physics community, especially during the past three decades. The therapeutic and diagnostic possibilities arising from such technology include site‐specific drug delivery within the central nervous system, advancement of techniques for navigation and selective catheterization of vessels within the cardiovascular and cerebrovascular systems, and the nonsurgical exploration of the alimentary and respiratory tracts. In this review, we examine the physical principles underlying in vivo magnetic manipulation systems, and catalog the various types of instrumentation used for such purposes to date. Thereafter, we evaluate the different methods of image‐based localization used to identify the position of the probe within the body. Finally, we appraise an emerging technology known as nonlinear magnetic stereotaxis, a technique that permits minimally invasive access to difficult‐to‐approach parts of the brain. We close the review with a few comments on the directions for future work within this field.
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87.80.-y Biophysical techniques (research methods)
87.59.-e X-ray imaging

Novel discharge circuit for a multijoule TEA CO2 laser

P. K. Bhadani and R. G. Harrison

Rev. Sci. Instrum. 65, 563 (1994); http://dx.doi.org/10.1063/1.1145118 (4 pages)

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A novel discharge circuit that reduces significantly the amount of energy conducted by the switch in a TEA CO2 laser is reported. We demonstrate this circuit on a working multijoule TEA CO2 laser in which the switch is shown to conduct typically only 5% of the total input pulse energy. The laser has worked reliably in gas mixtures that place stringent demands on the discharge and circuit. It has produced an output of 7 J at an efficiency of 9.6% using a CO2:N2:He (1:1:4) gas mixture at atmospheric pressure and further using a helium‐free gas mixture (CO2:N2:H2 at 400 mbar) it has produced a maximum efficiency of 14.6% for an output of 7.8 J. The great simplicity and high efficiency of the new discharge circuit allow it to be incorporated in the existing laser designs with minimal modifications.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers

A new detection method used to calibrate Fabry–Perot interferometers in the infrared range

M. Talvard, C. Javon, M. Garcin, and D. Thouvenin

Rev. Sci. Instrum. 65, 567 (1994); http://dx.doi.org/10.1063/1.1145119 (8 pages)

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Fabry–Perot interferometers are routinely used in the Tore Supra tokamak in order to measure the time evolution of the electron temperature of the confined plasmas. Calibration of such interferometers requires the detection of very low dc levels (0.1 nV) with signal‐to‐noise ratios less than 10−5, which is generally not compatible with standard detection methods. A new correlation method is proposed to achieve this absolute calibration. It is based on a proper noise autocorrelation technique combined with an optimized filtering involving Fourier analysis. The advantages of the method are detailed and experimentally compared to standard averaging techniques, such as coherent addition and synchronous detection. The method can be used in a more general context every time very small amplitude signals are to be measured.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
07.60.Ly Interferometers

The minimization of ac phase noise in interferometric systems

I. Filinski and R. A. Gordon

Rev. Sci. Instrum. 65, 575 (1994); http://dx.doi.org/10.1063/1.1145120 (12 pages)

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A simple step‐by‐step procedure, including several novel techniques discussed in the Appendices, is given for minimizing ac phase noise in typical interferometric systems such as two‐beam interferometers, holographic setups, four‐wave mixers, etc. Special attention is given to index of refraction fluctuations, direct mechanical coupling, and acoustic coupling, whose importance in determining ac phase noise in interferometric systems has not been adequately treated. The minimization procedure must be carried out while continuously monitoring the phase noise which can be done very simply by using a photodiode measurement of the interferometer output. Supplementary measurements using a microphone and accelerometer will also be helpful in identifying the sources of phase noise. Emphasis is placed on new techniques or new modifications of older techniques which will not usually be familiar to most workers in optics. Thus, the necessity of eliminating the effects of index of refraction fluctuations which degrade the performance of all interferometers is pointed out as the first priority. A substantial decrease of the effects of all vibrating, rotating, or flowing masses (e.g., cooling lines) in direct contact with the optical table will also have to be carefully carried out regardless of the type of interferometric system employed.
It is recommended that this be followed by a simple, inexpensive change to a novel type of interferometer discussed in Appendix A which is inherently less sensitive to mechanical vibration. Such a change will lead to a reduction of both low‐frequency and high‐frequency ac phase noise by more than an order of magnitude and can be carried out for all interferometers with the exception of multiple pass optical systems and high‐resolution FFT spectrometers. It is pointed out that most homemade air bladder vibration isolators are used incorrectly and do not provide sufficient reduction in the contribution of floor vibrations to phase noise. Several simple trampoline‐type air bladder vibration isolator systems are described which are comparable in performance to commercial systems. With the exception of very nonrigid or undamped optical tables, the dominant source of ac phase noise at this point will usually be due to acoustic coupling to the optical components and mounts themselves. This means not only that the optical components and mounts must be rigid but that the mechanical coupling between the table and the mounts, as well as the coupling between the mounts and components themselves, be as rigid as possible.
An additional damping of optical mounts beyond that generally found in commercial mountings will also have to be carried out to obtain a further reduction of phase noise. A simple damping technique employing an additional mass and an intermediate damping layer is described which will significantly improve the performance of both homemade and commercial optical mounts. Similar damping techniques which are especially suitable for homemade optical tables and breadboards are also considered.
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07.60.Ly Interferometers

Incorporation of a differential refractometer into a laser light‐scattering spectrometer

Chi Wu and Ke‐Qing Xia

Rev. Sci. Instrum. 65, 587 (1994); http://dx.doi.org/10.1063/1.1145121 (4 pages) | Cited 37 times

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A new differential refractometer, which mainly consists of a laser light source, a position‐sensitive detector, and a temperature‐controlled refractometer cuvette has recently been developed. In comparison with a conventional differential refractometer, it has a different optical design so that the effect of laser beam drift can be greatly reduced. In our design, a very small pinhole is illuminated by the laser light and the illuminated pinhole is imaged to the detector by a lens located in the middle between the detector and the pinhole in a 2f‐2f configuration. The cuvette is placed just before the lens. The pinhole, the cuvette, the lens, and the detector are mounted on a small optical rail. The refractometer can be easily incorporated into any laser light‐scattering spectrometer, in which the laser, the thermostat, and the computer are shared. This not only reduces the total cost (at least ten times cheaper than a commercial differential refractometer), but also enables us to measure the specific refractive index increment and the scattered light intensity under the identical experimental conditions, such as wavelength and temperature. This novel refractometer has a wide linear detection range (±0.035 RI units) with a resolution of 10−6 RI units, which is sufficient for determining the specific refractive index increment of most polymer solutions.
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07.60.Hv Refractometers and reflectometers
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers

Conversion of the Finnigan‐MAT TSQ‐70 thermospray ionization interface to an electrospray ionization interface

Sharon Jackett and Mehdi Moini

Rev. Sci. Instrum. 65, 591 (1994); http://dx.doi.org/10.1063/1.1145122 (6 pages) | Cited 5 times

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The conversion of a thermospray ionization (TSI) feature of a Finnigan‐MAT TSQ‐70 mass spectrometer to electrospray ionization (ESI) and its performance are described. The existing source, pumping capacity, flanges, and temperature controller of the TSQ‐70 TS feature were used with a few modifications. Conversion of the commercial TS option to a simple and economically viable ES option has made the analysis of large biomolecules possible without expensive upgrades. To preserve the simplicity of the conversion, desolvation is effected by a heated‐capillary tube (HCT). The HCT and its housing are inserted inside the TSQ‐70 TS flange like a solid probe. Mass spectrometric results of low and high molecular weight biomolecules, the mass accuracy, sensitivity, and charge states of the observed ions are comparable to published results by other laboratories. Adequate spectral quality was obtained at short scan times, a required characteristic for interfacing ESI with separation methods such as capillary zone electrophoresis.
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07.75.+h Mass spectrometers
87.80.-y Biophysical techniques (research methods)

A laser‐aided prealigned pinhole collimator for synchrotron x rays

Benjamin Chu, Paul J. Harney, Yingjie Li, Kung Linliu, Fengji Yeh, and Benjamin S. Hsiao

Rev. Sci. Instrum. 65, 597 (1994); http://dx.doi.org/10.1063/1.1145123 (6 pages) | Cited 14 times

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A pinhole small‐angle x‐ray scattering (SAXS) instrument was constructed at the SUNY X3A2 beamline, National Synchrotron Light Source, Brookhaven National Laboratory. The three pinholes were mounted in a thick‐walled stainless steel pipe and prealigned by using a portable laser source and a charge‐coupled device (CCD) area detector. After the prealignment, incorporation of the collimator to the synchrotron x‐ray source required only maximization of the incident x‐ray intensity passing through the pinholes, which could be done easily by using a scintillation counter after proper attenuation. The entire synchrotron SAXS instrument setup took only a few hours even without stepping motor control for the pinhole collimator unit. By combining this collimator with a CCD‐based x‐ray area detector which could be assembled by using commercially available components, the SAXS instrument showed good performance for structural scales up to an order of 100 nm. The CCD‐based x‐ray area detector used a computer‐ (or manually) controlled intensified unit with a variable gain setting in order to accommodate the changing x‐ray flux and to protect the detector from over exposure, a necessary feature for operation of an area detector at a synchrotron light source.
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41.60.Ap Synchrotron radiation
41.50.+h X-ray beams and x-ray optics
41.85.Si Particle beam collimators, monochromators

A microalignment system for high precision positioning of collimating pinholes

W. Fischer, N. Rando, A. Peacock, and R. Venn

Rev. Sci. Instrum. 65, 603 (1994); http://dx.doi.org/10.1063/1.1145124 (5 pages) | Cited 2 times

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A complete micropositioning unit based on high precision, manually controlled X‐Y‐Z translators, related metrology system, and sighting microscope is described. It has been specifically developed for the alignment of collimating pinholes (5–10 μm diam) on cryogenic x‐ray detectors, 10–50 μm in size, deposited both on transparent and opaque substrates. The main characteristics of this flexible and convenient system are the capability to handle a complete test fixture ready for further measurements at cryogenic temperature, coupled with the possibility to verify the precision attained. Such microalignment equipment will find application in optical/UV/x‐ray photon counting experiments, whenever a highly collimated illumination is required or in any test involving precision positioning of small experimental units onto microdevices or detectors.
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07.85.-m X- and γ-ray instruments
06.60.Sx Positioning and alignment; manipulating, remote handling

The Howard Hughes Medical Institute cassette for storage phosphor plates

J.‐L. Staudenmann, W. L. Zotterman, D. W. Cook, C. M. Ogata, and W. A. Hendrickson

Rev. Sci. Instrum. 65, 608 (1994); http://dx.doi.org/10.1063/1.1145125 (4 pages)

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New cassettes for 201 mm×252 mm (8″×10″) and 201 mm×400 mm (8″×15.75″) storage phosphor plates have been developed at the Synchrotron Resource of the Howard Hughes Medical Institute. The purpose for this work was mainly twofold. Firstly, to diminish the number of manual operations when putting the storage phosphor plate into the cassette or when extracting it from the cassette. Secondly, to render such a cassette much lighter than the former metal cassette previously in use. These two goals were achieved by making new cassettes that are operated as one piece instead of two or three independent parts as with the former systems. The cassettes have been extensively tested and found to be very useful.
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06.90.+v Other topics in metrology, measurements, and laboratory procedures (restricted to new topics in section 06)

Inert gas purgebox for Fourier transform ion cyclotron resonance mass spectrometry of air‐sensitive solids

Michael A. May and Alan G. Marshall

Rev. Sci. Instrum. 65, 612 (1994); http://dx.doi.org/10.1063/1.1145126 (5 pages)

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A sealed rigid ‘‘purgebox’’ makes it possible to load air‐ and/or moisture‐sensitive solids into the solids probe inlet of a Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometer. A pelletized sample is transferred (in a sealed canister) from a commercial drybox to a Lucite(R) purgebox. After the box is purged with inert gas, an attached glove manipulator is used to transfer the sample from the canister to the solids probe of the mass spectrometer. Once sealed inside the inlet, the sample is pre‐evacuated and then passed into the high vacuum region of the instrument at ∼10−7 Torr. The purgebox is transparent, portable, and readily assembled/disassembled. Laser desorption FT/ICR mass spectra of the air‐ and moisture‐sensitive solids, NbCl5. NbCl2(C5H5)2, and Zr(CH3)2(C5H5)2 are obtained without significant oxidation. The residual water vapor concentration inside the purgebox was measured as 100±20 ppm after a 90‐min purge with dry nitrogen gas. High‐resolution laser desorption/ionization mass spectrometry of air‐sensitive solids becomes feasible with the present purgebox interface. With minor modification of the purgebox geometry, the present method could be adapted to any mass spectrometer equipped with a solid sample inlet.
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07.75.+h Mass spectrometers
07.30.Bx Degasification, residual gas
FREE

RELAX: An ultrasensitive, resonance ionization mass spectrometer for xenon

J. D. Gilmour, I. C. Lyon, W. A. Johnston, and G. Turner

Rev. Sci. Instrum. 65, 617 (1994); http://dx.doi.org/10.1063/1.1145127 (9 pages) | Cited 23 times

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RELAX is a resonance ionization, time‐of‐flight mass spectrometer to which a cryogenic sample concentrator has been added. This has resulted in an increase in sensitivity by a factor greater than 100. The sample concentrator consists of a localized cold spot in the ion source, onto which the sample condenses, and a heating laser to release the condensed sample into the ionization region. The lifetime against detection of a sample atom is close to 20 min, which corresponds to a count rate of 1 cps from a sample of 1000 atoms, while the mass resolution is 300 (10% peak height). Sensitivity depends on the return time of sample atoms to the cold spot (10 s) and the fraction of these atoms subsequently ionized (∼1%). The minimum sample size which can be measured is limited only by blank, which is currently 2×10−15 cc STP total xenon and isotopically atmospheric (this can be attributed to the large aliquots of xenon admitted to the instrument during development, and so may be expected to decrease with time). The precision of abundance measurements has been improved by the incorporation of pulse height discrimination and pulse counting detection for the less abundant isotopes. The design, construction, and operation of the spectrometer in its new configuration are described with particular attention to abundance extraction. The effects of the sample concentrator on ionization efficiency and discrimination are discussed in detail, as are interferences from nonresonantly ionized hydrocarbons and the means of accounting for them.
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07.75.+h Mass spectrometers

Design and implementation of a low temperature near‐field scanning optical microscope

Robert D. Grober, Timothy D. Harris, Jay K. Trautman, and Eric Betzig

Rev. Sci. Instrum. 65, 626 (1994); http://dx.doi.org/10.1063/1.1145128 (6 pages) | Cited 59 times

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The design and implementation of a low temperature (T≥1.5 K), near‐field scanning optical microscope are described herein. This microscope, which is based on the recently developed tapered fiber probe, is optimized for luminescence imaging and spectroscopy of mesoscopic semiconductor systems.
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07.60.Pb Conventional optical microscopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

A scanning electron microscope based microindentation system

A. M. Daniel, S. T. Smith, and M. H. Lewis

Rev. Sci. Instrum. 65, 632 (1994); http://dx.doi.org/10.1063/1.1145129 (7 pages) | Cited 3 times

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The design and characterization of a scanning electron microscope based microindentor is presented. Dynamic, high magnification imaging of the indentor–specimen contact zone is possible, permitting observation of indent events. Applied load as a function of indentor tip displacement is continuously monitored during indentation. The maximum applied load capability of 20 N is measured to a resolution of 1 mN with a piezoelectric transducer mounted on the indentor shaft. Displacement is measured with a specially developed capacitance gauge that is again mounted on the indentor shaft near the indentor tip and records tip displacement with respect to the specimen surface to a resolution of 10 nm over a 100 μm range. The instrument is vacuum compatible, capable of remote operation, has a short measurement loop, and a potentially high bandwidth response. Results from a fiber push‐down test on a SiC fiber reinforced glass ceramic are reported to illustrate the capability of the instrument in performing measurements across the nanoindentation and microindentation ranges.
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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)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Atomic force microscope with magnetic force modulation

Ernst‐Ludwig Florin, Manfred Radmacher, Bernhard Fleck, and Hermann E. Gaub

Rev. Sci. Instrum. 65, 639 (1994); http://dx.doi.org/10.1063/1.1145130 (5 pages) | Cited 48 times

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We have constructed a scanned stylus atomic force microscope (AFM) with direct force modulation and integrated microfluorescence optics. The instrument was designed to image the surface of massive samples under various ambient conditions. In force modulation microscopy the imaging force is modulated during the scanning process via an external magnetic field that acts directly on the magnetic AFM tip. Polymeric Langmuir–Blodgett films on silicon oxide were imaged to evaluate the application range of the instrument. We demonstrate that direct force modulation microscopy permits the quantitative recording of the local complex compliance both as a function of the location and as a function of the frequency. In a novel imaging mode referred to as sample resonance mode, the contrast of the image can be selectively enhanced based on local elasticity differences.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Difference between the forces measured by an optical lever deflection and by an optical interferometer in an atomic force microscope

Satoru Fujisawa, Masahiro Ohta, Takefumi Konishi, Yasuhiro Sugawara, and Seizo Morita

Rev. Sci. Instrum. 65, 644 (1994); http://dx.doi.org/10.1063/1.1145131 (4 pages) | Cited 13 times

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Using a simple model, we investigated the difference between the forces measured by an atomic force microscope (AFM) with an optical lever deflection method and that with an optical interferometer method. Then, using a mica with an atomically flat surface as a test sample, we confirmed experimentally the above difference, which says that the optical lever deflection method detects not only the surface corrugation but also the frictional force, while the optical interferometer method detects only the surface corrugation. Based on the above results, we proposed a method to measure the three‐dimensional force vector by using both the optical lever AFM/LFM and the optical interferometer AFM simultaneously. Furthermore, we mention that the measurement of three‐dimensional spatial distribution of the force vector will implement the computed tomography technique into AFM measurements, which yields a three‐dimensional spatial distribution of the force origin.  
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Charge exchange of hydrogen atoms in carbon foils at 0.4–120 keV

M. Gonin, R. Kallenbach, and P. Bochsler

Rev. Sci. Instrum. 65, 648 (1994); http://dx.doi.org/10.1063/1.1145132 (5 pages) | Cited 5 times

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Charge exchange properties of H atoms passing through thin carbon foils at incident energies from 0.5 to 120 keV/u are discussed in the context of charge transfer models. A model is presented in which the charge state equilibrium in the solid is explained by the overlap of the atomic and the solid‐state electron wave functions in k space. Outside the solid, near the surface, charge exchange occurs by tunneling of electrons between the carbon surface and the exiting projectile.
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34.70.+e Charge transfer
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

A microchopper for neutral beams

K. Kuhnke, K. Kern, R. David, B. Lindenau, and G. Comsa

Rev. Sci. Instrum. 65, 653 (1994); http://dx.doi.org/10.1063/1.1145133 (4 pages) | Cited 1 time

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A mechanical beam chopper with small dimensions is presented. The shape of the generated neutral beam pulses is calculated and experimental results are discussed. The microchopper is based on the operation principle of neutron choppers. It is operated in vacuum and generates molecular beam pulses at a repetition rate of 10 kHz with pulse lengths easily adjustable between 5 and <1 μs. The chopper can be used for time‐of‐flight applications and inherently acts as a high velocity pass filter.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
41.85.Ct Particle beam shaping, beam splitting

Removal of the plasma contained in an atomic beam produced by electron beam heating

Hironori Ohba, Akihiko Nishimura, Koichi Ogura, and Takemasa Shibata

Rev. Sci. Instrum. 65, 657 (1994); http://dx.doi.org/10.1063/1.1145134 (4 pages) | Cited 5 times

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Removal of the plasma contained in a gadolinium atomic beam produced by electron beam heating was investigated. A positive or negative electric potential was applied to the plasma removal electrodes which were a pair of parallel electrodes put along the atomic beam. When a positive potential was applied to the plasma removal electrodes, the plasma could not be removed at high evaporation rates. On the other hand, the plasma could be removed by applying a high negative potential to both removal electrodes, even at high evaporation rates. The potentials applied to the electrodes required to remove the plasma were estimated using the model that a plasma at ground potential flows with the atomic beam; ions are extracted from the plasma by negatively biased removal electrodes. The estimated potentials required to remove the plasma agreed well with experimental values.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors

A tunable microwave plasma source for space plasma simulation experiments

David N. Walker, Dwight Duncan, John A. Stracka, Jeffrey H. Bowles, Carl L. Siefring, Mark M. Baumback, and Paul Rodriguez

Rev. Sci. Instrum. 65, 661 (1994); http://dx.doi.org/10.1063/1.1145135 (8 pages) | Cited 8 times

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In laboratory experiments related to space plasma physics it is often desirable to produce plasmas with characteristics as close as possible to various naturally occurring plasma regimes. In the near‐earth region space plasma densities typically vary from 103–107 cm−3 and temperatures range from a few tenths of an eV to the order of 1 eV. The plasma parameters of electron density, electron temperature, and ion species are primary variables which are often not easy to reproduce in a chamber environment which is dependent upon conventional gas discharge or arc sources for plasma production. A simple microwave discharge device was developed which is easily tunable and capable of producing the moderate range of electron densities without an external magnetic field. The Asmussen‐type microwave plasma source described here covers and exceeds the parameter ranges required, is relatively easy to construct, and is inexpensive. The device makes use of an air dielectric coaxial coupler to couple magnetron output to a resonant cavity. Estimates of effective electric fields and source densities and temperatures suggest that similar devices can easily be constructed and fashioned to produce these parameters, depending upon requirements, over a wide range of values. The use of widely available commercial magnetrons manufactured for microwave ovens allows a certain ease in the construction of these devices in that available cavity Q’s can range to lower levels and therefore resonant lengths can be adjusted more easily. The design is discussed relative to desired experimental parameter ranges and some discussion is given of expected source current densities, electric fields, and temperature ranges.
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52.80.Pi High-frequency and RF discharges
52.65.-y Plasma simulation
52.50.Dg Plasma sources
95.30.Qd Magnetohydrodynamics and plasmas

Long plasma generation using microwave slot antennas on a rectangular waveguide

Hirokazu Tahara, Jiro Kitayama, Toshiaki Yasui, Ken‐ichi Onoe, Yasuji Tsubakishita, and Takao Yoshikawa

Rev. Sci. Instrum. 65, 669 (1994); http://dx.doi.org/10.1063/1.1145136 (4 pages) | Cited 2 times

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30‐cm‐class long plasmas were generated using 2.45‐GHz microwave slot antennas on a rectangular waveguide with a T‐shaped ridge for the development of high performance ion sources or for plasma reactors for large‐area material processing. The microwave coupling efficiencies above 85% were achieved for Ar, N2, and O2 over large flow rate ranges. From the electric fields on the inner wall E side of the waveguide, standing waves with the maximum electric field strength of about 30 kV/m were expected to be excited in the waveguide, depending on the location of the T‐shaped ridge. The plasma density for Ar was in the order of 1017 m−3 and for N2 and O2 1016 m−3 in a discharge chamber in front of the slot antennas. The electron temperature for Ar ranged from 3 to 4 eV and for N2 and O2 from 3 to 8 eV. The spatial profiles of the ion saturation current for Ar were almost flat in the discharge chamber although the profiles for N2 and O2, with large flow rates or near the antennas, were slightly rough.
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52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges

Production of high‐density sheet plasma by an rf magnetron device with high‐frequency operation

Kenji Murata, Yoshihiro Okuno, and Hiroharu Fujita

Rev. Sci. Instrum. 65, 673 (1994); http://dx.doi.org/10.1063/1.1145137 (5 pages) | Cited 2 times

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Production of a sheet plasma with a high electron density is successfully realized in an rf magnetron device with a rectangular hollow cathode by operating at a high driving frequency. The electron density ne of the sheet plasma increased up to about 2×1011 cm−3 with the relation of ne∝f2 for f≤20 MHz at a fixed driving voltage, and tended to saturate for f≳20 MHz. This saturation frequency is found to exceed the value in a conventional rf discharge by about four times. A hollow electrode with a size larger than the optimum value decreased the electron density slightly and produced electrons with two temperatures. The frequency dependencies of the rf oscillating potentials at the electrode and in the plasma were also studied to explain the results.
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52.50.Dg Plasma sources
52.80.Tn Other gas discharges

The adverse effect of perpendicular ion drift flow on cylindrical triple probe electron temperature measurements

D. L. Tilley, A. D. Gallimore, A. J. Kelly, and R. G. Jahn

Rev. Sci. Instrum. 65, 678 (1994); http://dx.doi.org/10.1063/1.1145138 (4 pages) | Cited 13 times

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The cylindrical triple probe method is an attractive technique for measuring electron temperatures (Te) and electron number densities (ne) in a variety of plasmas sources. In practice, however, the cylindrical triple probe can be sensitive to sources of error that affect all Langmuir probe techniques. In particular, the presence of an ion drift velocity component that is perpendicular to the probe axis has been known to result in erroneous measurements of ne. Less obvious, however, is that ion flow perpendicular to the probe has a significant effect on the indicated Te. The purpose of this note is to make researchers aware of such an effect and to demonstrate a technique which can mitigate it. The approach taken to investigate this phenomenon was to make Te measurements in the plume of a 20 kW magnetoplasmadynamic thruster with the probe oriented at several angles with respect to the local ion flow.
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52.70.Ds Electric and magnetic measurements

A modified ultrasonic interferometer for sound velocity measurements in molten metals and alloys

Ph. M. Nasch, M. H. Manghnani, and R. A. Secco

Rev. Sci. Instrum. 65, 682 (1994); http://dx.doi.org/10.1063/1.1145139 (7 pages) | Cited 1 time

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An ultrasonic interferometer has been developed for measuring compressional wave velocity (VP) and attenuation (or conversely, quality factor QP) in molten Fe, Fe‐Ni, Fe‐Ni‐S, and Fe‐Ni‐Si alloys. Results for pure molten Fe are presented. A radio frequency (rf) induction technique is used for heating that allows a ±1 K temperature stability at 1973 K. The effects of the electromagnetic field interaction with the molten conductive metal are discussed in terms of applicability to VP and QP measurements. Considerations of acoustic impedance and thermal absorption are presented to discuss the high‐temperature use of polycrystalline Al2O3 buffer rods for velocity and attenuation measurements. Viscoelastic theories, when applied to pure molten Fe, predict an extremely small acoustic coefficient of attenuation. Suggestions are made to circumvent the experimental difficulties encountered in attenuation measurements.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.58.Dj Sound velocity

An instrument for the heat flux measurement from a contour of a surface with uniform temperature

J. W. Baughn, M. A. Hoffman, and Daehee Lee

Rev. Sci. Instrum. 65, 689 (1994); http://dx.doi.org/10.1063/1.1145140 (6 pages) | Cited 1 time

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An instrument for the measurement of the heat flux distribution along an internal or external contour of a surface with a uniform temperature is described. The main element in this instrument is an electrically heated narrow nickel/chromium ribbon which is mounted flush with, but thermally and electrically insulated from, walls on all sides. The walls are separately heated and are made of a highly conducting material (e.g., aluminum) to ensure a uniform temperature. Differential thermocouples are used to measure the temperature difference between the walls and Ni/Cr ribbon at various positions along the ribbon. The ribbon power is adjusted until the differential temperature is nulled at a particular position on the ribbon. Since conduction along the ribbon is small, the electrical power divided by the sensor area is a direct measure of the surface heat flux at the nulled position. This makes it possible to measure the local time‐average heat flux at various positions along a contour of a surface inside a circular duct. The time constant in this application was 13 s. An uncertainty analysis shows that this instrument has an uncertainty of ±3.84% for a convective heat flux on the order of 900 W/m2.
Show PACS
07.20.Fw Calorimeters
68.35.Md Surface thermodynamics, surface energies
05.70.Ce Thermodynamic functions and equations of state

A noncontact measurement technique for the specific heat and total hemispherical emissivity of undercooled refractory materials

Aaron J. Rulison and Won‐Kyu Rhim

Rev. Sci. Instrum. 65, 695 (1994); http://dx.doi.org/10.1063/1.1145087 (6 pages) | Cited 36 times

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A noncontact measurement technique for the constant pressure specific heat (cpl) and the total hemispherical emissivity (ϵTl) of undercooled refractory materials is presented. In purely radiative cooling, a simple formula which relates the post‐recalescence isotherm duration and the undercooling level to cpl is derived. This technique also allows us to measure ϵTl once cpl is known. The experiments were performed using the high‐temperature high‐vacuum electrostatic levitator at JPL in which 2–3 mm diameter metallic samples can be levitated, melted, and radiatively cooled in vacuum. The averaged specific heats and total hemispherical emissivities of Zr and Ni over the undercooled regions agree well with the results obtained by drop calorimetry: cpl,av(Zr)=40.8±0.9 J/mol K, ϵTl,av(Zr)=0.28±0.01, cpl,av(Ni)=42.6±0.8 J/mol K, and ϵTl,av(Ni)=0.16±0.01.
Show PACS
07.20.Fw Calorimeters
07.20.Ka High-temperature instrumentation; pyrometers
65.20.-w Thermal properties of liquids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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