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Feb 1999

Volume 70, Issue 2, pp. 1233-1576

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Exponential analysis in physical phenomena

Andrei A. Istratov and Oleg F. Vyvenko

Rev. Sci. Instrum. 70, 1233 (1999); http://dx.doi.org/10.1063/1.1149581 (25 pages) | Cited 124 times

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Many physical phenomena are described by first-order differential equations whose solution is an exponential decay. Determining the time constants and amplitudes of exponential decays from the experimental data is a common task in semiconductor physics (deep level transient spectroscopy), biophysics (fluorescence decay analysis), nuclear physics and chemistry (radioactive decays, nuclear magnetic resonance), chemistry and electrochemistry (reaction kinetics) and medical imaging. This review article discusses the fundamental mathematical limitations of exponential analysis, outlines the critical aspects of acquisition of exponential transients for subsequent analysis, and gives a comprehensive overview of numerical algorithms used in exponential analysis. In the first part of the article the resolution of exponential analysis as a function of noise in input decays is discussed. It is shown that two exponential decays can be resolved in a transient only if the ratio of their time constants is greater than the resolution limit, which can be explicitly calculated from the signal-to-noise ratio in the transient. Although the signal-to-noise ratio is generally limited by the sensitivity of the equipment, it is shown that digitalization of the decays may be a major source of noise. The requirements for type of analog-to-digital converter, number of digitized data points and duration of digitized transients, which must be met to obtain the theoretical resolution limit and to improve stability of the exponential analysis, are formulated. The second part of the review article gives an overview and comparison of major numerical techniques of exponential analysis, such as the nonlinear least squares fit, the Prony method, the method of modulating functions, the method of moments, the Laplace–Padé approximation, the Tikhonov regularization method, the Gardner transformation, the method of maximum entropy and others. © 1999 American Institute of Physics.
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02.60.Lj Ordinary and partial differential equations; boundary value problems
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back to top OPTICS; ATOMS and MOLECULES; SPECTROSCOPY

An active spectrometer

N. H. Brooks, D. F. Finkenthal, T. H. Jensen, N. N. Naumenko, and S. N. Tugarinov

Rev. Sci. Instrum. 70, 1258 (1999); http://dx.doi.org/10.1063/1.1149582 (6 pages)

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This article describes a new type of correlation spectrometer, dubbed an “active spectrometer.” It utilizes an oscillating mirror in a 1/4-m-Rowland circle spectrometer configuration to displace the spectrum periodically in the dispersion direction relative to fixed exit slits. The wavelength of the light passing through each slit is modulated sinusoidally at the mechanical oscillation frequency and its intensity is measured with a spot detector such as a photomultiplier or photodiode. With a PC-based control/data acquisition system, the signal from each detector is sampled digitally at a frequency constrained to be an integral multiple of the mirror drive frequency. From the resultant phase locking between the signal sampling and the mirror oscillation, it follows that the correlation function between the signal and mirror phase angle is obtained simply by averaging the data from successive mirror scans. Such a scan-averaged spectrum with low noise may then be compared with digitally stored reference spectra obtained through the same instrument. ac coupling of detector and amplifier results in rejection of continuum light and, when photodiodes are used as detectors, the maximization of preamplifier gain. © 1999 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
42.79.Pw Imaging detectors and sensors
07.05.Hd Data acquisition: hardware and software
07.05.Dz Control systems
85.60.Gz Photodetectors (including infrared and CCD detectors)

Fabrication of binary phase surface relief optical elements by selective deposition of dielectric layers

N. Davidson, R. Ozeri, and R. Baron

Rev. Sci. Instrum. 70, 1264 (1999); http://dx.doi.org/10.1063/1.1149583 (4 pages) | Cited 1 time

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We propose and demonstrate a new scheme to fabricate surface relief binary phase elements by using selective deposition of dielectric layers through a contact mask. By using in situ optical thickness monitoring, accurate (∼1%), repeatable, and robust layer thicknesses are readily obtained, leading to accurate phases. We demonstrate our scheme by forming a circular π phase element that is used to form a dark optical trap for atoms. © 1999 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Wc Optical coatings
42.79.Dj Gratings
42.86.+b Optical workshop techniques

Investigation of etched silicon wafers for lobster-eye optics

A. G. Peele

Rev. Sci. Instrum. 70, 1268 (1999); http://dx.doi.org/10.1063/1.1149584 (6 pages) | Cited 2 times

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See Also: Erratum

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We investigate some high aspect ratio etched silicon to determine its suitability as a lobster-eye optic. The major defects present leading to performance degradation are identified and tolerance goals are set for prospective candidates. © 1999 American Institute of Physics.
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42.79.-e Optical elements, devices, and systems
07.85.-m X- and γ-ray instruments
78.66.Db Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Dd Experimental determination of defects by diffraction and scattering

Characterization of a novel micromachined optical vibrating rate gyroscope

D. J. Seter, O. Bochobza-Degani, E. Socher, S. Kaldor, E. Scher, and Y. Nemirovsky

Rev. Sci. Instrum. 70, 1274 (1999); http://dx.doi.org/10.1063/1.1149585 (3 pages)

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The present article presents experimental results measured on a new class of micromachined rate-gyroscope, incorporating integrated optical sensing. A hybrid cantilever type device was fabricated by bulk micromachining, bonded to a complementary metal-oxide-semiconductor chip and encapsulated in a vacuum package. The proof mass is electrostatically actuated and the mechanical output motion is sensed by modulated integrative differential optical sensing method. Characterization of the device, including measurements of the natural frequencies and angular rate, is reported. Noise measurements indicate noise equivalent rate of 10−2–10−3 deg/s/√Hz. Currently the measured minimum detectable rate is 1 deg/s due to experimental setup limitations.© 1999 American Institute of Physics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Hyper-Rayleigh scattering using 1907 nm laser excitation

M. A. Pauley and C. H. Wang

Rev. Sci. Instrum. 70, 1277 (1999); http://dx.doi.org/10.1063/1.1149586 (8 pages) | Cited 18 times

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The experimental setup used to perform hyper-Rayleigh scattering at the near infrared wavelength of 1907 nm is described. The setup described is employed to measure the first molecular hyperpolarizabilities, β, of three new thiophene-based nonlinear optical chromophores. Although scattering at this wavelength is weak and the experiment requires great care, use of it allows one to obtain near dispersion-free first hyperpolarizability. Comparing the results with those obtained on the same chromophores using the 1064 nm excitation, we show that the two state model, which is commonly used to relate the β values at different wavelengths, fails to correlate the results at these two excitation wavelengths. © 1999 American Institute of Physics.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.An Optical susceptibility, hyperpolarizability
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
42.70.Jk Polymers and organics
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Line focus system with a segmented prism array for compact x-ray laser experiments

Naohiro Yamaguchi, Tadayuki Ohchi, Chiemi Fujikawa, Asuka Ogata, Yoshiyuki Hisada, Kazunobu Okasaka, Tamio Hara, Teruyoshi Tsunashima, and Yutaka Iizuka

Rev. Sci. Instrum. 70, 1285 (1999); http://dx.doi.org/10.1063/1.1149632 (3 pages) | Cited 2 times

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We have designed a new focusing system with a five-segmented prism array in combination with a beam expander and cylindrical lens assembly for compact x-ray laser experiments using a yttrium–aluminum–garnet (YAG) laser. The focusing characteristics were examined from irradiation patterns on a target. It was found that a beam of 25 mm diameter whose intensity profile was not uniform was condensed to a focused line having about 12 mm length and 50 μm width with a flat intensity distribution along the line on average, though the small-scale intensity modulation due to interference among the beamlets was observed. Spectroscopic observation of the plasma produced by irradiating the YAG laser of 2 J energy onto an Al slab target showed that highly ionized ions were produced up to the Li-like ionic stage. The new lens system is useful for compact x-ray laser research. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.55.Vc X- and γ-ray lasers
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Bh Lenses, prisms and mirrors
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Monochromatic focusing of subpicosecond x-ray pulses in the keV range

T. Missalla, I. Uschmann, E. Förster, G. Jenke, and D. von der Linde

Rev. Sci. Instrum. 70, 1288 (1999); http://dx.doi.org/10.1063/1.1149587 (12 pages) | Cited 36 times

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An effective x-ray optical method to focus keV x-ray pulses shorter than one picosecond by using spherically or toroidally bent crystals is presented. The spectral, spatial, and time-dependent properties of focusing by two-dimensional bent crystals are calculated by considering geometrical effects, physical limitation in high performance crystal optics, and reflectivities obtained by x-ray diffraction theory. These properties are compared with first experimental results of focusing x rays from a plasma created by a laser pulse with 4.5 mJ energy and 100 fs pulse length. The x-ray signals, simultaneously obtained from a von Hámos spectrometer and two-dimensional bent crystals are compared and found in good agreement with theoretical data. The possibilities and aspects of laser pump x-ray probe experiments using this type of x-ray optics system and currently available laser systems are discussed. © 1999 American Institute of Physics.
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41.50.+h X-ray beams and x-ray optics

A cost-effective method for minimizing the sphere-of-confusion error of x-ray microdiffractometers

I. C. Noyan, S. K. Kaldor, P.-C. Wang, and J. Jordan-Sweet

Rev. Sci. Instrum. 70, 1300 (1999); http://dx.doi.org/10.1063/1.1149588 (5 pages) | Cited 14 times

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Microdiffractometers are used to obtain x-ray diffraction data from regions that are tens of microns or less in size. If a microdiffractometer’s rotation circles do not share the same center, or if the feature of interest on a sample does not lie at the center of all rotations, the sample feature will, upon rotation of the diffractometer circles, precess through a finite volume known as the sphere of confusion (SoC). If the size of the beam used for diffraction analysis is smaller than the SoC diameter, the beam may actually move off the region of interest. In this article, we describe a new technique, based on x-ray fluorescence imaging and coordinate transforms, which can maintain the sample position to within ±6 μm over all rotations even when a commercial diffractometer is used as the base for the microdiffractometer system. In this scheme, a grid held in place on the specimen surface is mapped using fluorescent radiation at various sample tilts. The transformation matrices, which relate the grid coordinates to the sample stage coordinates at different sample tilts, can then be used to bring the sample stage into coincidence with its original position. © 1999 American Institute of Physics.
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07.85.Jy Diffractometers
07.85.Qe Synchrotron radiation instrumentation
06.60.Sx Positioning and alignment; manipulating, remote handling
61.05.cp X-ray diffraction

Cavity ring down spectroscopy on radicals in a supersonic slit nozzle discharge

Tomasz Motylewski and Harold Linnartz

Rev. Sci. Instrum. 70, 1305 (1999); http://dx.doi.org/10.1063/1.1149589 (8 pages) | Cited 34 times

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A sensitive and generally applicable technique for direct absorption spectroscopy on electronic transitions of transient species in the gas phase is presented. The method is based on cavity ring down spectroscopy in a pulsed slit nozzle, incorporating a discharge in a high pressure supersonic expansion. The performance is demonstrated with spectra of the 000 origin band of the 2Π←X2Π electronic transition of the isoelectronic linear carbon chain radicals C6H and C6H2+. Rotationally resolved and rotationally cold spectra (Trot<15 K) have been obtained. The sensitivity of the technique is demonstrated for anions with a detection limit as low as 107 C2− molecules cm−3 for rovibrational transitions of the B2Σu+←X2Σg+ system. © 1999 American Institute of Physics.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
82.50.-m Photochemistry
52.80.Hc Glow; corona
33.20.Ea Infrared spectra
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Single molecule force spectrometer with magnetic force control and inductive detection

A. Schemmel and H. E. Gaub

Rev. Sci. Instrum. 70, 1313 (1999); http://dx.doi.org/10.1063/1.1149590 (5 pages) | Cited 10 times

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Mechanical investigations with single molecules have opened a rich spectrum of new experiments, ranging from molecular recognition over polymer elasticity and DNA unzipping to protein unfolding. Here we present the design of a novel instrument, where the force is applied to the molecule via magnetic fields acting on a magnetic cantilever for atomic force microscopy. The performance of this instrument was demonstrated by measuring the binding force of biotin/avidin complexes. A new and technically very appealing detection scheme for measurements of unbinding forces was introduced, which consists of picking up the induced voltage pulse caused by a discontinuous change of the magnet position upon bond rupture. © 1999 American Institute of Physics.
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07.79.Pk Magnetic force microscopes
87.64.Dz Scanning tunneling and atomic force microscopy
07.79.Lh Atomic force microscopes
87.15.-v Biomolecules: structure and physical properties

New design of a cryostat-mounted scanning near-field optical microscope for single molecule spectroscopy

Yannig Durand, Jörg C. Woehl, Bertrand Viellerobe, Wolfgang Göhde, and Michel Orrit

Rev. Sci. Instrum. 70, 1318 (1999); http://dx.doi.org/10.1063/1.1149591 (8 pages) | Cited 7 times

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Due to the weakness of the fluorescence signal from a single fluorophore, a scanning near-field optical microscope for single molecule spectroscopy requires a very efficient setup for the collection and detection of emitted photons. We have developed a home-built microscope for operation in a l-He cryostat which uses a solid parabolic mirror in order to optimize the fluorescence collection efficiency. This microscope works with Al-coated, tapered optical fibers in illumination mode. The tip-sample separation is probed by an optical shear-force detection. First results demonstrate the capability of the microscope to image single molecules and achieve a topographical resolution of a few nanometers vertically and better than 50 nm laterally. © 1999 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
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
87.64.mt Near-field scanning
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Compact and freely movable single atom detector

P. Westphal, S. Koch, A. Horn, J. Schmand, and H. J. Andrä

Rev. Sci. Instrum. 70, 1326 (1999); http://dx.doi.org/10.1063/1.1149592 (7 pages) | Cited 1 time

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A compact fluorescence detector has been developed which allows to count slow, single Na atoms. By using glass fibers for the exciting and the fluorescence light we obtained free movability of the detector. The detection efficiency has been analyzed and optimized by an extensive investigation of all processes concerning the laser-induced fluorescence, especially the random walk of the atom, saturation effects, and optical pumping. Single atoms are identified by registration of photon bursts which stand out from the Poisson distributed background. An absolute calibration of the detection efficiency has been achieved by a time-resolved fluorescence measurement in combination with a corresponding Monte–Carlo simulation. Atomic fluxes well below 1 atom/s can be determined with an uncertainty of less than ±10%. Assuming a continuous flux of 1 atom/s with 25 m/s typically about 50% of these atoms are counted. The detector is an excellent tool for differential scattering experiments with slow atomic beams. © 1999 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
07.60.Dq Photometers, radiometers, and colorimeters
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
07.77.Gx Atomic and molecular beam sources and detectors
32.50.+d Fluorescence, phosphorescence (including quenching)
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
32.80.Xx Level crossing and optical pumping

Conceptual development and characterization of a diamond-based ultraviolet detector

Wei Jiang, Jaeshine Ahn, Chan Yuen Chuen, and Lam Yee Loy

Rev. Sci. Instrum. 70, 1333 (1999); http://dx.doi.org/10.1063/1.1149593 (8 pages) | Cited 8 times

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A metal–semiconductor–metal (MSM) structure ultraviolet (UV) photodetector has been designed and fabricated on chemical vapor deposition grown diamond and its performance has been characterized. A concept was envisioned of creating a new process by which 1 μm small gap spacing was achieved. This kind of detector can be operated at a lower bias voltage with a higher photoresponsivity in the UV range. The success of this device depended on the bilayer metal electrodes, good Ohmic contact, image reversal technique, direct writing process, and sacrificial layer technology. Current–voltage and capacitance–voltage characteristics, photoresponsivity, and quantum efficiency of planar MSM structures with Au/Ti–diamond contacts are presented. © 1999 American Institute of Physics.  
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85.60.Gz Photodetectors (including infrared and CCD detectors)

A beam position sensor for low power infrared laser diodes

Lorenzo Capineri, Leonardo Masotti, Marina Mazzoni, Guido Toci, and Piero Mazzinghi

Rev. Sci. Instrum. 70, 1341 (1999); http://dx.doi.org/10.1063/1.1149594 (8 pages) | Cited 4 times

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This article presents the design criteria, the prototype development, and application results of a low-cost four quadrants infrared (IR) detector. The detector was specifically developed as a position sensor for the alignment of low power IR laser diode beams, especially for spectroscopic applications. The detector consists of a polyvinilidene difluoride pyroelectric radiation sensor of 4×4 mm2 total surface area and of a four-channel high gain transimpedance amplifier, followed by a narrow bandwidth resonant filter for noise rejection. The overall single pixel responsivity resulted 3590 V root mean square /math at 5.8 μm, and modulation frequency of 85 Hz. The beam spot centroid of a square-wave modulated laser diode emitting 85 μmath was determined using an algorithm evaluating the difference signals between diagonal elements along vertical and horizontal scanning directions. An uncertainty in the centroid position of 6 μm, in both directions, was obtained, mainly limited by the digitizing resolution of the 12-bit acquisition system. © 1999 American Institute of Physics.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.55.Px Semiconductor lasers; laser diodes
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Hydrostatic optical cell for temperatures below 350 K and pressures to 400 MPa

J. Bruce Johnson

Rev. Sci. Instrum. 70, 1349 (1999); http://dx.doi.org/10.1063/1.1149595 (3 pages) | Cited 2 times

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A compact optical pressure cell tested at pressures up to 400 MPa is presented. The cell has been used within the temperature range 10–350 K. The cell has a small mass of 0.2 kg which facilitates rapid changes in temperature. A new high-pressure window seal is presented which allows the cell to be mounted directly in vacuum with no leak over its entire temperature and pressure range. A method of attaching the cell to common coldhead-type cryostats and closed-cycle refrigerators is presented. © 1999 American Institute of Physics.
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07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.60.-j Optical instruments and equipment

Optoelectronic standardization of laser Doppler perfusion monitors

A. Liebert, P. Lukasiewicz, D. Boggett, and R. Maniewski

Rev. Sci. Instrum. 70, 1352 (1999); http://dx.doi.org/10.1063/1.1149596 (3 pages) | Cited 8 times

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An optoelectronic method for standardization of laser Doppler (LD) instruments is proposed and tested. The optoelectronic standardization is based on detection of modulated near-infrared light from a light emitting diode (LED) emitted into the optic probe (detecting fiber) of the LD instrument. Changes of the frequency and amplitude of the light enables evaluation of the sensitivity and linearity of the instrument response. Measurements of the LD instrument response show linear increase of perfusion signal with the modulation frequency of light. Analysis of the LD signal components (flux, speed, concentration) show that for fixed amplitude and varying frequency of the modulation, the flux and speed are linearly related to the frequency and the concentration is constant. The linear increase of flux and concentration signals was observed for increasing amplitude of modulation with fixed frequency. The proposed technique allows for automatic evaluation of the instrument response. © 1999 American Institute of Physics.
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42.62.Be Biological and medical applications
87.63.L- Visual imaging
87.19.U- Hemodynamics
87.19.Wx Pneumodyamics, respiration
06.20.F- Units and standards
87.19.rh Fluid transport and rheology
back to top CHARGED PARTICLE SOURCES, OPTICS and ACCELERATION

Linac-based free electron lasers and e-beam energy modulation

U. Bizzarri, G. Dattoli, and P. L. Ottaviani

Rev. Sci. Instrum. 70, 1355 (1999); http://dx.doi.org/10.1063/1.1149597 (4 pages) | Cited 2 times

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We discuss the effect of the energy modulation over the macropulse of an e-beam driving a free electron lasers oscillator. It is shown that this modulation produces an efficient cavity depletion and provides an output optical beam, chopped at the same frequency of the beam energy modulation. The advantages offered by this method are discussed, with particular reference to the case of intracavity harmonic generation. The effective realization of an electron beam energy modulating device is finally discussed. © 1999 American Institute of Physics.
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41.60.Cr Free-electron lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
29.27.Eg Beam handling; beam transport
41.85.Ct Particle beam shaping, beam splitting
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
29.20.-c Accelerators
41.75.Ht Relativistic electron and positron beams

Peak-detector-hold based circuit for trigger synchronization of the electron beam and wiggler in a free-electron laser experiment

A. V. Ravi Kumar, K. K. Mohandas, K. Sathyanarayana, and K. K. Jain

Rev. Sci. Instrum. 70, 1359 (1999); http://dx.doi.org/10.1063/1.1149633 (3 pages) | Cited 1 time

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A simple circuit based on the principle of peak detect and hold has been designed, tested, and used for efficient and reliable synchronization of the triggering of the relativistic electron beam and the electromagnet wiggler that are used in a pulsed, millimeter wave free-electron laser experiment. This circuit is found to be reliable in operation and has a jitter of less than 2% for a fixed wiggler current. © 1999 American Institute of Physics.  
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41.60.Cr Free-electron lasers
42.60.By Design of specific laser systems
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.30.Sk Pulse and digital circuits

Emittance measurements of the Sub-Picosecond Accelerator electron beam using beam position monitors

Steven J. Russell

Rev. Sci. Instrum. 70, 1362 (1999); http://dx.doi.org/10.1063/1.1149598 (5 pages) | Cited 1 time

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In general, the spatial distributions of electron beams from photoinjectors are unknown and are not well approximated by a Gaussian. Therefore, when measuring the emittance, it is important to make no assumptions about the beam’s spatial distribution. A diagnostic that fulfills this requirement uses beam position monitors to measure the second moment of the electron beam’s image charge. This information, coupled with the beam line’s transfer matrix, can be used as an unambiguous measure of the root mean square emittance that is independent of the beam’s spatial distribution. Presented here are the results of the first implementation of this measurement technique on the Sub-Picosecond Accelerator facility at Los Alamos National Laboratory. © 1999 American Institute of Physics.
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29.27.Fh Beam characteristics
41.75.Fr Electron and positron beams
29.27.Ac Beam injection and extraction
41.85.Ar Particle beam extraction, beam injection

Effect of a metal–dielectric structure introduced in the plasma chamber of the Frankfurt 14 GHz electron cyclotron resonance ion source

L. Schächter, K. E. Stiebing, S. Dobrescu, Al. I. Badescu-Singureanu, L. Schmidt, O. Hohn, and S. Runkel

Rev. Sci. Instrum. 70, 1367 (1999); http://dx.doi.org/10.1063/1.1149634 (3 pages) | Cited 8 times

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A new approach of the possibility to significantly increase the high charge state ion beams delivered by electron cyclotron resonance (ECR) ion sources by using metal–dielectric (MD) structures characterized by high secondary electron emission properties is presented. The intensities of argon ion beams extracted from the 14 GHz electron cyclotron resonance ion source of the Institut für Kernphysik (IKF) der Johann Wolfgang Goethe-Universität in Frankfurt/Main were measured when a 26 mm diam disk of a specially treated MD structure (Al–Al2O3) was introduced axially close to the ECR plasma. The Ar beam intensities and charge-state distributions obtained with this disk are compared to measurements with disks of iron and pure aluminum at the same position relative to the plasma. All measurements were performed with the disk at the plasma chamber potential. The results with the MD structure show a net shift of the beam intensity towards higher charge states as compared with the other disk materials. Enhancement factors of the beam current of up to 10 (for Ar12+) when using a MD disk compared to the output when using an aluminum disk and up to 40 (for Ar11+) when using an iron disk were measured. © 1999 American Institute of Physics.    
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams
52.50.Dg Plasma sources

Atmospheric pressure ion focusing in a high-field asymmetric waveform ion mobility spectrometer

Roger Guevremont and Randy W. Purves

Rev. Sci. Instrum. 70, 1370 (1999); http://dx.doi.org/10.1063/1.1149599 (14 pages) | Cited 66 times

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The focusing of ions at atmospheric pressure and room temperature in a high-field asymmetric waveform ion mobility spectrometer (FAIMS) has been investigated. FAIMS operates with the application of a high-voltage, high-frequency asymmetric waveform across parallel plates. This establishes conditions wherein an ion migrates towards one of the plates because of a difference in the ion mobility at the low and high electric field conditions during application of the waveform. The migration can be stopped by applying a dc compensation voltage (CV) which serves to create a “balanced” condition wherein the ion experiences no net transverse motion. This method has also been called “transverse field compensation ion mobility spectrometry” and “field ion spectrometry®.” If this experiment is conducted using a device with cylindrical geometry, rather than with flat plates, an ion focusing region can exist in the annular space between the two concentric cylinders. Ion trajectory modeling showed that the behavior of the ions in the cylindrical geometry FAIMS analyzer was unlike any previously described atmospheric pressure ion optics system. The ions appeared to be trapped, or focused by being caught between two opposing forces. Requirements for establishing this focus for a given ion were identified: the applied waveform must be asymmetric, the electric field must be sufficiently high that the mobility of the ion deviates from its low-field value during the high-voltage portion of the asymmetric waveform, and finally, the electric field must be nonuniform in space (e.g., cylindrical or spherical geometry). Experimental observations with a prototype FAIMS device, which was designed to measure the radial distribution of ions in the FAIMS analyzer region, have confirmed the results of ion trajectory modeling. © 1999 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
41.85.-p Beam optics
07.77.Ka Charged-particle beam sources and detectors
07.75.+h Mass spectrometers

Microwave diagnostics in electron cyclotron resonance plasma sources

B. Larousse and P. Louvet

Rev. Sci. Instrum. 70, 1384 (1999); http://dx.doi.org/10.1063/1.1149600 (3 pages)

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The plasma source, which is of high importance in the optimization of the separation of the gadolinium isotopes by the plasma separation process, requires a precise knowledge of its physical characteristics. Thus, a diagnostic has been developed to estimate the microwave power inside the source. A microstrip antenna has been designed and developed in order to characterize the microwave field at 36 GHz frequency in the plasma source. The experimental results for different plasma regimes are presented. The measurements inside the plasma source show a maximum of microwave absorption for an argon pressure of 10−4 mbar with 93% absorption of the incident wave in the conditions of isotope separation. © 1999 American Institute of Physics.
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52.70.Gw Radio-frequency and microwave measurements
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.70.Ds Electric and magnetic measurements
52.50.Dg Plasma sources
back to top NUCLEAR PHYSICS, FUSION and PLASMAS

Self-similarity of plasma networking in a broad range of length scales: From laboratory to cosmic plasmas

A. B. Kukushkin and V. A. Rantsev-Kartinov

Rev. Sci. Instrum. 70, 1387 (1999); http://dx.doi.org/10.1063/1.1149576 (5 pages) | Cited 11 times

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A newly developed method of high-resolution processing, called a method of multilevel dynamical contrasting, is applied to analyze numerous data from laboratory electric discharges and observations of cosmic plasmas in a broad spectroscopic range from rf to soft x-ray images. A high degree of self-similarity of plasma structuring is found in a very broad range of length scales, from individual filaments in laboratory discharges to the structures in the universe, which resemble electric currents networking in laboratory plasmas. The results presented illustrate recently suggested [Kukushkin and Rantsev-Kartinov, Laser Part. Beams 16, 445 (1998)] generic features of networking in plasmas: (1) long-living (nonfluctuative) filamentation of electric current; (2) formation of a fractal structure made of single filament and complicated interaction of these “fractal” filaments; (3) formation of a percolating network that includes, in particular, formation of the “stockings” woven by the individual filaments. © 1999 American Institute of Physics.
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52.65.-y Plasma simulation
95.30.Qd Magnetohydrodynamics and plasmas
52.25.Mq Dielectric properties
52.70.Ds Electric and magnetic measurements
52.70.La X-ray and γ-ray measurements

Plasma networking in magnetically confined plasmas and diagnostics of nonlocal heat transport in tokamak filamentary plasmas

A. B. Kukushkin and V. A. Rantsev-Kartinov

Rev. Sci. Instrum. 70, 1392 (1999); http://dx.doi.org/10.1063/1.1149577 (5 pages) | Cited 2 times

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The method of multilevel dynamical contrasting is applied to analyzing available data from tokamak plasmas. The results illustrate a possibility of extending the concept of the plasma percolating networks in dense Z pinches (and other inertially confined plasmas) to the case of magnetically confined plasmas. This extension suggests a necessity to append the conventional picture of the nonfilamentary plasma (which is nearly a fluid described by conventional magnetohydrodynamics) with a “network” component which is formed by the strongest long-living filaments of electric current and penetrate the “fluid” component. Signs of networking are found in visible light and soft x-ray images, and magnetic probing data. A diagnostic algorithm is formulated for identifying the role of plasma networking in observed phenomena of nonlocal (non-diffusive) heat transport in a tokamak. © 1999 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.Ds Electric and magnetic measurements
52.25.Kn Thermodynamics of plasmas
52.30.-q Plasma dynamics and flow
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