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Jan 1994

Volume 65, Issue 1, pp. 1-274

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An energy dispersive x‐ray absorption spectroscopy beamline, X6A, at NSLS

P. L. Lee, M. A. Beno, G. Jennings, M. Ramanathan, G. S. Knapp, K. Huang, J. Bai, and P. A. Montano

Rev. Sci. Instrum. 65, 1 (1994); http://dx.doi.org/10.1063/1.1144778 (6 pages) | Cited 24 times

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An energy dispersive x‐ray absorption spectroscopy instrument has been built at the X6A beam port of the x‐ray ring at the National Synchrotron Light Source (NSLS). This instrument allows the collection of extended x‐ray‐absorption fine structure and/or x‐ray absorption near‐edge structure spectra for many elements on the millisecond time scale. The beamline employs a four‐point crystal bender and a rectangular Si 220 crystal to access incident energies between 6.5 and 21 keV. Because the polychromator focuses the synchrotron beam to a narrow 100‐μm line, this experimental apparatus is ideal for x‐ray absorption spectroscopy experiments in special environments such as at high pressures, for in situ experiments, and/or for very small samples. In this manuscript we will describe the instrument design and present data with which to evaluate the instrument. This beamline is available through the NSLS user proposal system.
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07.85.-m X- and γ-ray instruments

A table‐top x‐ray microbeam scanning facility

A. Attaelmanan, S. Larsson, A. Rindby, P. Voglis, and A. Kuczumow

Rev. Sci. Instrum. 65, 7 (1994); http://dx.doi.org/10.1063/1.1144750 (6 pages) | Cited 12 times

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The x‐ray microbeam scanning facility in our laboratory at Chalmers University of Technology/Göteborg University is described in terms of optical and mechanical design, imaging capacity, spatial resolution, and sensitivity. Different types of visualization of the elemental distribution are demonstrated and application of image processing is discussed. Examples of applications in the field of single‐particle analysis as well as tree ring analysis are given. Future perspectives of the technique are also discussed.
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07.85.-m X- and γ-ray instruments

Low energy x‐ray spectrometer for an electron beam ion trap

P. Beiersdorfer and B. J. Wargelin

Rev. Sci. Instrum. 65, 13 (1994); http://dx.doi.org/10.1063/1.1144786 (5 pages) | Cited 46 times

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A flat‐crystal spectrometer for analyzing ultrasoft x rays in the wavelength region 10–25 Å was constructed for use on an electron beam ion trap. The spectrometer employs a position‐sensitive proportional counter for detection and affords a nominal resolving power of 2000 at a Bragg angle of 45°. Measurements of the L‐shell spectra of Ne‐like Fe16+ and of the 3s1/2–3p3/2 transitions in near Na‐like Pb71+, which fall into the wavelength region from 13.5 to 17.5 Å, are presented demonstrating high throughput and excellent signal‐to‐noise characteristics. The actual resolving power achieved was limited by the intrinsic resolution of the crystal to 500. A resolving power close to the nominal value was achieved in second order Bragg reflection.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
32.30.Rj X-ray spectra
52.70.La X-ray and γ-ray measurements

In‐laboratory stopped‐flow extended x‐ray absorption fine structure apparatus in the dispersive mode for determination of the structure of short‐lived intermediates

Yasuhiro Inada, Shigenobu Funahashi, and Hitoshi Ohtaki

Rev. Sci. Instrum. 65, 18 (1994); http://dx.doi.org/10.1063/1.1144775 (7 pages) | Cited 8 times

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We have constructed an in‐laboratory stopped‐flow extended x‐ray absorption fine structure (EXAFS) apparatus by combining laboratory EXAFS equipment in the dispersive mode and a stopped‐flow unit with two 150‐μm‐thick boron nitride windows. The rotating anode x‐ray generator with a Mo target was used as an x‐ray source. The self‐scanning photodiode array was adopted as a position sensitive‐linear x‐ray detector. In order to obtain a suitable x‐ray flux intensity, the accumulation of weak intensities during a short gate time was carried out by repeating the measurements. We have confirmed the performance of our apparatus by repeatedly measuring a number of static EXAFS spectra of 0.20 mol dm−3 aqueous solution of copper(II) sulfate. By use of our newly developed apparatus, we have succeeded in the direct determination of the structure of the reaction intermediate, the heterodinuclear copper(II)/mercury(II) complex, formed in the copper(II) ion incorporation into the homodinuclear mercury(II) complex of 5,10,15,20‐tetrakis(4‐sulfonatophenyl)porphine.
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82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
61.66.Hq Organic compounds

Simple removal method of diffraction peaks in x‐ray absorption fine structure spectra from a single crystal in the fluorescence mode

Shuichi Emura and Hironobu Maeda

Rev. Sci. Instrum. 65, 25 (1994); http://dx.doi.org/10.1063/1.1144793 (3 pages) | Cited 1 time

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A simple method has been proposed for the removal of diffraction peaks from x‐ray absorption fine structure spectra of a single crystal observed in the fluorescence mode (i.e., excitation spectrum), in which the diffraction peaks inevitably appear. With a patching up of the appropriate spectrum regions from the spectra having many diffraction peaks, it is shown that we can synthesize one spectrum without the diffraction peaks. Here, several spectra are observed in rotating the single crystal within small angles. As an example, this method is successfully applied in finding the local structure around the Cr3+ ion in a single crystal of α‐Al2O3:Cr3+. The bond distances of Cr3+–O2− have been determined as r1=2.04 Å and r2=1.95 Å, those are closer to the bond distances in Cr2O3.
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78.70.Dm X-ray absorption spectra
78.70.En X-ray emission spectra and fluorescence

A 10‐J electric‐discharge‐pumped phototriggered XeCl laser

Yu. Bychkov, M. Makarov, A. Suslov, and A. Yastremsky

Rev. Sci. Instrum. 65, 28 (1994); http://dx.doi.org/10.1063/1.1144742 (6 pages) | Cited 5 times

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An electric‐discharge‐pumped XeCl laser using phototriggering by x rays is reported. A consistent input of the stored energy into the pumping discharge plasma has been realized. An output pulsed energy of about 10 J has been achieved in a ∼3‐l active volume with an efficiency ≳2%. High spatial uniformity of the laser radiation and a stable space discharge were observed. A stability analysis of the discharge pumping has been made for the XeCl laser in terms of the current‐voltage characteristic model. The method for parametric optimization of such systems is described.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

High resolution stimulated Brillouin gain spectrometer

W. Tandy Grubbs and Richard A. MacPhail

Rev. Sci. Instrum. 65, 34 (1994); http://dx.doi.org/10.1063/1.1144743 (8 pages) | Cited 9 times

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We describe a stimulated Brillouin gain (SBG) spectrometer based on low power continuous‐wave frequency‐stabilized lasers. The high resolution and broad tuning range of this spectrometer are demonstrated through a SBG spectrum of glycerol in the glassy state (T=146 K). The narrow Brillouin linewidth (17 MHz half‐width at half‐maximum) and large Brillouin shift (17.31 GHz) in this spectrum illustrate the extremely high equivalent ‘‘finesse’’ of the instrument, a finesse that would be difficult to achieve through interferometric techniques. The accuracy and precision with which the Brillouin shift can be measured are demonstrated using SBG spectra of liquid methylene chloride as an example. Our Brillouin shift values obtained over the temperature range 178–300 K are in excellent agreement with values measured previously by others using spontaneous and stimulated Brillouin scattering.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
42.62.Fi Laser spectroscopy
07.60.Rd Visible and ultraviolet spectrometers

Stabilization and precise calibration of a continuous‐wave difference frequency spectrometer by use of a simple transfer cavity

E. Riedle, S. H. Ashworth, J. T. Farrell, and D. J. Nesbitt

Rev. Sci. Instrum. 65, 42 (1994); http://dx.doi.org/10.1063/1.1144744 (7 pages) | Cited 46 times

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A novel, simple, and inexpensive calibration scheme for a continuous‐wave difference frequency spectrometer is presented, based on the stabilization of an open transfer cavity by locking onto the output of a polarization stabilized HeNe laser. High frequency, acoustic fluctuations of the transfer cavity length are compensated with a piezoelectric transducer mounted mirror, while long term drift in cavity length is controlled by thermal feedback. A single mode Ar+ laser, used with a single mode ring dye laser in the difference frequency generation of 2–4 μm light, is then locked onto a suitable fringe of this stable cavity, achieving a very small long term drift and furthermore reducing the free running Ar+ linewidth to about 1 MHz. The dye laser scan provides tunability in the difference frequency mixing process, and is calibrated by marker fringes with the same stable cavity. Due to the absolute stability of the marker cavity, precise frequency determination of near infrared molecular transitions is achieved via interpolation between these marker fringes. It is shown theoretically that the residual error of this scheme due to the dispersion of air in the transfer cavity is quite small, and experimentally that a frequency precision on the order of 1 MHz per hour is routinely obtained with respect to molecular transitions.  
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
42.62.Fi Laser spectroscopy

Computer controlled in situ radiolysis electron spin resonance spectrometer incorporating magnetic field‐microwave frequency locking

Keith P. Madden, Hugh J. D. McManus, and Richard W. Fessenden

Rev. Sci. Instrum. 65, 49 (1994); http://dx.doi.org/10.1063/1.1144745 (9 pages) | Cited 3 times

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A lab‐built personal computer‐based electron spin resonance (ESR) spectrometer is described which incorporates a wide range magnetic field/microwave frequency lock as part of its magnetic field control subsystem. Instrument operation is accomplished by keyboard commands, with important experimental variables logged automatically for reference during subsequent data analysis. The spectrometer features both narrowband field modulation and direct‐detection time‐resolved ESR modes. The data acquisition system and field/frequency lock operate such that spectrum recordings consisting of multiple magnetic field sweeps are undistorted by long‐term klystron frequency drift. The spectrometer features low noise microwave preamplification, balanced mixer detection, automatic reference arm phase control, and a fast automatic frequency control system requiring no klystron frequency modulation. Natural abundance 13C and 33S studies of the terephthalic acid radical trianion and sulfite radical anion are presented as proof of spectrometer performance.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.50.Kx Processes caused by X-rays or γ-rays

Spline‐based deconvolution technique in electron paramagnetic resonance imaging

Giuseppe Placidi, Marcello Alecci, and Antonello Sotgiu

Rev. Sci. Instrum. 65, 58 (1994); http://dx.doi.org/10.1063/1.1144746 (5 pages) | Cited 3 times

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The article presents a modification to the spline deconvolution technique. The method was developed within the framework of electron paramagnetic resonance imaging and is particularly useful in cases of low signal‐to‐noise ratio (S/N) and when the deconvolution kernel is a large fraction (about 50%) of the studied function. The modified spline deconvolution method works directly in the signal space and does not require a low‐pass filter that causes loss of information and limits the resolution as is the case of Fourier deconvolution. The comparison was done with Fourier deconvolution and was based on three parameters that account for resolution, noise, and proportion stability. Experimental tests were done using two nitroxide‐free radicals of different linewidths (0.05 and 0.16 mT, respectively) at different gradient values (between 0.05 and 0.2 mT/m). Modified spline deconvolution gave consistently better results in all the three parameters, particularly at the lower gradient values. For this reason the method is useful in in vivo experiments where the low S/N does not permit use of high gradient values.
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87.61.-c Magnetic resonance imaging
87.64.K- Spectroscopy

Probehead with interchangeable loop‐gap resonators and rf coils for multifrequency EPR/ENDOR

T. Christides, W. Froncisz, T. Oles, and James S. Hyde

Rev. Sci. Instrum. 65, 63 (1994); http://dx.doi.org/10.1063/1.1144747 (5 pages) | Cited 3 times

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A probehead employing interchangeable loop‐gap resonators and rf coils for multifrequency EPR/ENDOR spectroscopy from 1 to 10 GHz is described. A precision coupling mechanism allows accurate magnetic coupling of the microwaves to the resonators. The Rexolite© support of the resonator acts as a spool for the ENDOR coil. rf fields of 1.0 mT are generated. The coil and resonator can be easily changed to cover the range of 1–10 GHz. Liquid‐phase ENDOR spectra of the stable free‐radical galvanoxyl and of the spin label TEMPONE (4‐oxo‐2,2,6,6‐tetramethyl‐l‐piperidine‐N‐oxyl) dissolved in n‐heptane are shown. The ENDOR enhancement for nitrogen from TEMPONE is 15 times larger at 2.3 than at 9.3 GHz due to the rf enhancement.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Dielectric resonator‐based stopped‐flow electron paramagnetic resonance

Andrzej Sienkiewicz, Kunbin Qu, and Charles P. Scholes

Rev. Sci. Instrum. 65, 68 (1994); http://dx.doi.org/10.1063/1.1144748 (7 pages) | Cited 19 times

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We present the technical details and relevant performance aspects of a dielectric resonator‐based electron paramagnetic resonance probe for stopped‐flow kinetic studies. The major benefits of this system are: (1) It incorporates a small, high sensitivity resonator system that is insensitive to stopped‐flow induced noisy transients. (2) The resonator system is cheap, robust, and easily assembled. (3) It contains a microwave coupling scheme that provides finesse in tuning and freedom from microphonics.
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82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.20.-w Chemical kinetics and dynamics
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Ultrahigh vacuum surface science chamber with integral scanning tunneling microscope

Andrew J. Leavitt, Taejoon Han, John M. Williams, Roger S. Bryner, David L. Patrick, Carol E. Rabke, and Thomas P. Beebe

Rev. Sci. Instrum. 65, 75 (1994); http://dx.doi.org/10.1063/1.1144749 (5 pages) | Cited 7 times

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The construction of an ultrahigh vacuum (UHV) surface science chamber equipped with the standard surface analytical techniques and a connected companion UHV chamber containing a scanning tunneling microscope (STM) has been completed. The novel aspects of this experimental system are: the combination of many spatially averaging techniques with STM; a sample holder which is capable of in situ transfer between these various capabilities; variable temperature operation; in situ tip‐sample approach without mechanical feedthroughs; and various novel software aspects. The sample transfer mechanism allows the sample to be transferred onto the main manipulator and heated or cooled with thermocouple monitoring while electrical isolation from the chamber ground is maintained. The sample then can be transferred in vacuo to the UHV STM for further study. STM tips can be transferred into and out of vacuum and positioned for sputtering and UHV analysis. The various design details which allow for in vacuo transfers will be discussed.
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07.30.Hd Vacuum testing methods; leak detectors
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

A scanning tunneling microscope suitable for biological applications

Antonio Cricenti, Renato Generosi, and Stefano Selci

Rev. Sci. Instrum. 65, 80 (1994); http://dx.doi.org/10.1063/1.1144751 (5 pages) | Cited 6 times

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We have designed and built a scanning tunneling microscope (STM) suitable for biological applications. A sound‐isolated chamber contains the STM unit; the chamber can be evacuated or filled with inert gas, after the sample and tip are loaded, in order to reduce contamination on sample and tip. The STM unit is mounted inside two separable cylindrical supports. The lower cylinder contains the sample holder mounted on top of a step‐motor controlled x‐y‐z stage, while the upper one contains the piezoelectric tip scanner. An I/V converter preamplifier mounted inside the x‐y‐z stage and a completely digitized feedback circuit, together with a full software package in UNIX X‐window environment and data processing, allow fast sample–tip approach and reduced acquisition time. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) in air and reproducible large scan on a platinum grating are routinely obtained. Images of human liver ferritin deposited on an activated gold substrate have also been obtained.  
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87.64.Dz Scanning tunneling and atomic force microscopy

An integrated scanning tunneling, atomic force and lateral force microscope

L. A. Wenzler, T. Han, R. S. Bryner, and T. P. Beebe

Rev. Sci. Instrum. 65, 85 (1994); http://dx.doi.org/10.1063/1.1144752 (4 pages) | Cited 5 times

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We describe the design and operation of a combined scanning tunneling–atomic force–lateral force microscope [(STM), (AFM), (LFM)]. Including these capabilities in a single instrument reduces construction costs and increases flexibility. AFM and LFM may be performed simultaneously; a simple reconfiguration (requiring removing the AFM/LFM cantilever holder and replacing with a STM tip) changes the instrument into a STM. We present atomic forces depicted in force‐to‐distance curves and experimental imaging applications with all three techniques.
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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

An adaptive scan generator for a scanning tunneling microscope

P. Heuell, M. A. Kulakov, and B. Bullemer

Rev. Sci. Instrum. 65, 89 (1994); http://dx.doi.org/10.1063/1.1144753 (4 pages) | Cited 6 times

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A novel scan generator for a scanning tunneling microscope (STM) has been developed. The instrument compares tunneling current with three thresholds values, to generate an x‐scanner signal with a dynamically changeable step size for adaptation to sharp topographical changes. It has two advantages compared to conventional STM scan generators (i) a better protection from a tip crash and (ii) minimization of the image acquisition time. The implementation is made with a digital signal processor (DSP) DSP32C from AT&T, mounted on a commercially available PC AT‐compatible plug‐in card. Test images of extremely rough surfaces confirm the usefulness of our novel scan generator. The concept could also be used for different scanning probe microscopes.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

A small‐area high‐Tc superconducting bolometer with Y‐Ba‐Cu‐O thin film

Xizhi Li, Xiangqing Shi, Li Wang, Shuqin Li, Yizhi Qi, Bingchuan Yang, Xiaoping Wang, and Dongqi Shi

Rev. Sci. Instrum. 65, 93 (1994); http://dx.doi.org/10.1063/1.1144754 (4 pages)

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A small‐area high‐Tc superconducting bolometer with a dense YBCO meander wire on a (100) Zr(Y)O2 substrate has been tested at λ=1.5 μm using a diode laser as the radiation source. The infrared power absorbed by the bolometer was calibrated using a dc infrared substitution method. Responsivities of hundreds of V/W with a millisecond response time were obtained at a temperature of 86.5 K in the modulation frequency range of 10–3000 Hz. A minimum noise equivalent power of 6×10−11 W/Hz1/2 was measured at 1000 Hz. The experimental results are compared with those obtained from a thermal analysis of the substrate‐supported microbolometer. No nonbolometric effect was distinguished.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

Modeling of signal detection by using the photothermal probe beam deflection technique

Peter Zimmermann and Eberhard Welsch

Rev. Sci. Instrum. 65, 97 (1994); http://dx.doi.org/10.1063/1.1144755 (5 pages) | Cited 2 times

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Performing photothermal surface displacement (PTD) technique at λ=10.6 μm in a vacuum chamber, the measured signal is obtained by the change in probe beam deflection at the bulge of the reflecting heated sample surface. The influence of the accuracy‐limiting quantities such as angle of incidence of the probe beam as well as its finite lateral extension, and the detector geometry and the temperature‐dependent reflection at the sample surface has been investigated by a numerically performed simulation in order to optimize the measuring procedure. The maximum resolution power is achieved for probe beam diameters small compared to the heating beam diameter. An unambiguous measurement may be carried out satisfying the following condition between the quad‐cell slit width dslit, the probe beam diameter 2rPB, and the heating beam diameter 2rHB: 2rHB≥2rPB≫dslit keeping the probe beam angle of incidence αPB as small as possible. Moreover, it has been shown that the contribution of the temperature influenced reflection on the change of the probe beam intensity can be also neglected at λ=10.6 μm.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.70.-q Methods of materials testing and analysis

Rare‐earth phosphor laser‐induced fluorescence thermal imaging system

D. J. Bizzak and M. K. Chyu

Rev. Sci. Instrum. 65, 102 (1994); http://dx.doi.org/10.1063/1.1144780 (6 pages) | Cited 15 times

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This article examines the measurement capabilities of a novel, two‐dimensional thermal imaging system based on the fluorescence properties of an europium‐doped lanthanum oxysulfide (La2O2S:Eu+3) thermographic phosphor. The foundation of the technique (i.e., the fluorescence properties of La2O2S:Eu+3), as well as the design of the thermal imaging system, are also described. The technique that is employed in the design of the system utilizes the tripled output of a pulsed Nd:YAG laser to excite the thin phosphor coating applied to a test surface. The resulting fluorescent emission of the temperature sensitive 512‐nm radiative transition, along with that of the relatively temperature independent 620‐nm transition, is acquired using an image‐intensified charge coupled device camera. The ratio of the intensities of these two emissions, integrated during their decay, is then correlated with temperature. Phosphor calibration data that is presented demonstrate the efficacy of the technique, while results of evaluations to assess the spatial resolution and measurement accuracy provide a quantitative measure of system capabilities.
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07.20.Dt Thermometers

Deconvolution of unchopped time‐of‐flight waveforms

Brett R. Cameron and Peter W. Harland

Rev. Sci. Instrum. 65, 108 (1994); http://dx.doi.org/10.1063/1.1144781 (8 pages) | Cited 1 time

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A reliable method for deconvolving badly convoluted molecular beam time‐of‐flight waveforms using Fourier transform and Wiener filtering techniques is presented. The devised method places no restrictions on the functional form of any factors affecting the shape of the measured time‐of‐flight distribution, but rather uses an accurately determined distribution to estimate an overall response function for the system. The estimated response function may then be used to deconvolve any convoluted time‐of‐flight waveform measured under similar experimental conditions. The mathematical details of the method are discussed and examples of its application to the deconvolution of time‐of‐flight waveforms measured in unchopped pulsed supersonic beams of argon, krypton, CHCl3, and CH3Cl are presented.
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06.30.Gv Velocity, acceleration, and rotation
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Two‐stage parallel‐plate energy analyzer for simultaneous detection of positive, negative, and neutral particles

D. Calabrese, O. Yenen, L. M. Wiese, and D. H. Jaecks

Rev. Sci. Instrum. 65, 116 (1994); http://dx.doi.org/10.1063/1.1144782 (7 pages) | Cited 2 times

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We describe a unique apparatus that simultaneously measures the laboratory energy and angles of several charged particles formed in a single beam. The ability to separate and detect particles of opposite polarity allows one to measure them in coincidence. Equations for the trajectories of the particles are derived and discussed in detail. The expressions for the corresponding resolution of the detected particles are also presented. Data produced in recent experiments illustrate some of the analyzer’s more important features.
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41.85.Qg Particle beam analyzers, beam monitors, and Faraday cups
41.75.-i Charged-particle beams

H− and D− scaling laws for Penning surface‐plasma sources

H. Vernon Smith, Paul Allison, and Joseph D. Sherman

Rev. Sci. Instrum. 65, 123 (1994); http://dx.doi.org/10.1063/1.1144783 (6 pages) | Cited 5 times

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The small‐angle source (SAS), 4X source, and 8X source are Penning surface‐plasma sources that produce high‐current, high‐brightness H− ion beams for accelerator applications. The scaling from the SAS (1X source) to the 4X source, and from the 4X source to the 8X source is at least as good as predicted by the scaling laws. In many instances, the scaling is better than predicted, particularly in the critical area of the efficiency with which H− ions are produced per unit of discharge power. Using ζ=jH−/FC, where FC is the cathode power density load, ζ4X≊2ζSAS and ζ8X≊1.5ζ4X. The jH− scaling is at least as good as predicted by the scaling laws—we have been able to produce the predicted H− current in both the 4X and the 8X sources. The SAS was scaled up in size to the 4X source, and the 4X source was scaled up in size to the 8X source, on the assumption that the effective kTH−=5 eV. We also assume that the effective kTH−=the effective kTD−. These temperature scalings appear to be obeyed. The D− current scaling appears to be even better than assumed, namely, jD−≊jH−.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors

LIF probing with high spatial resolution in the process zone of a photolysis laser

W. Strube, M. Rossberg, J. Wollbrandt, and E. Linke

Rev. Sci. Instrum. 65, 129 (1994); http://dx.doi.org/10.1063/1.1144784 (6 pages) | Cited 3 times

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A laser‐induced fluorescence (LIF) method for spatially resolved fragment detection and characterization in the radiation field of a photolysis laser is described. Measurements of the radiation field of a focused beam showed up highly inhomogeneous irradiation conditions, resulting in a strong local dependence of the laser‐induced processes. The spatial resolution of the method is based on stepping‐motor‐controlled motion of the focusing lens of the photolysis laser versus the probe laser focused to a diameter (1/e2) of 58 μm. This diameter corresponds to the spatial inhomogeneities of the quantities studied in this article. However, the monitored volume (5.3×10−6 cm3) also represents a compromise between acceptable S/N ratio and spectral resolution. The advantages and limits of this spatially resolved fluorescence (SRF) technique are discussed. Owing to its simplicity it can be readily implemented in existing laser photolysis equipment with conventional LIF detection. This method is currently being applied to the study of IR laser chemical reactions. A few examples illustrate the range of applicability of the method by providing information on the fluence dependence of product formation, on mass transport kinetics of molecular species in the context of heterogeneous laser processing, and on the internal energy distribution of the dissociation products. They show the much higher information content of SRF measurements as compared with conventional LIF measurements.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light

Audio‐frequency discharge cleaning system for the SINP tokamak using single turn primary

P. Ranjan, A. K. Hui, S. Chowdhury, R. K. Paul, S. Basu, P. S. Bhattacharya, A. Bal, R. Ray, S. K. Majumdar, and N. K. Mukhopadhyay

Rev. Sci. Instrum. 65, 135 (1994); http://dx.doi.org/10.1063/1.1144785 (5 pages) | Cited 4 times

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Taking advantage of the iron core of the Saha Institute of Nuclear Physics (SINP) tokamak, a single turn primary coil was used to generate low power ohmically excited audio‐frequency hydrogen plasma to clean the SINP tokamak vacuum vessel of adsorbed gases. This scheme allowed us to easily use available low voltage power transistors and other existing power supply components to generate audio‐frequency voltage. Using this scheme the discharge cleaning system was tested successfully in a short period of 2–3 months. The system has been utilized to carry out initial discharge cleaning of the vessel as well as daily cleaning to achieve full designed parameters of our tokamak.
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52.55.Fa Tokamaks, spherical tokamaks
52.80.Vp Discharge in vacuum

The Gaseous Electronics Conference radio‐frequency reference cell: A defined parallel‐plate radio‐frequency system for experimental and theoretical studies of plasma‐processing discharges

P. J. Hargis, K. E. Greenberg, P. A. Miller, J. B. Gerardo, J. R. Torczynski, M. E. Riley, G. A. Hebner, J. R. Roberts, J. K. Olthoff, J. R. Whetstone, R. J. Van Brunt, M. A. Sobolewski, H. M. Anderson, M. P. Splichal, J. L. Mock, et al.

Rev. Sci. Instrum. 65, 140 (1994); http://dx.doi.org/10.1063/1.1144770 (15 pages) | Cited 193 times

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A ‘‘reference cell’’ for generating radio‐frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self‐bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.
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52.70.Gw Radio-frequency and microwave measurements
52.80.Hc Glow; corona
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