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Review of Scientific Instruments

Issue 1 • Date Jan 1995

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Displaying Results 1 - 25 of 307
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Review of plane grating focusing for soft x‐ray monochromators

    Page(s): 1 - 14
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    During the last 10 years various types of soft x‐ray monochromators have been developed, which are optically based on the plane grating focusing condition introduced in 1980. These instruments as well as those using the original 1980 optical configuration are reviewed and compared to the other type of high performance soft x‐ray grating monochromator, the Rowland circle based spherical grating monochromator (SGM). Performance data of a plane grating monochromator (HE‐PGM‐3), which was recently commissioned at BESSY and which offers a broad spectral range (40–2000 eV) and very high spectral resolution (up to E/ΔE∼10 000) are given in more detail. The performance of grating and crystal monochromators is compared in the 1–2 keV photon energy range. © 1995 American Institute of Physics. View full abstract»

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  • Laboratory grazing‐emission x‐ray fluorescence spectrometer

    Page(s): 15 - 19
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    We have developed a laboratory grazing‐emission x‐ray fluorescence (GEXRF) spectrometer. The instrument utilizes in vacuo wavelength‐dispersive detection. Due to the high resolution of a crystal monochromator at long wavelengths, the range of applicability of grazing x‐ray techniques is substantially extended to the longer wavelengths as compared to techniques used presently. It is demonstrated that interference fringes in the take‐off angle dependence of the fluorescent x‐ray intensity of a layered sample can be resolved using a conventional x‐ray tube. © 1995 American Institute of Physics. View full abstract»

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  • Concentration‐depth profiling using total‐reflection x‐ray fluorescence spectrometry in combination with ion‐beam microsectioning techniques

    Page(s): 20 - 23
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    A new method for the determination of vertical concentration profiles and its application to bilayer diffusion couples are presented. The method combines sputter sectioning techniques with ex situ total‐reflection x‐ray fluorescence (TXRF) analysis. It allows quantitative depth‐resolved analysis of alloys consisting of elements with atomic numbers ≥13, quantitatively and depth resolved. In contrast to other surface sensitive techniques like Auger electron spectrometry or secondary ion mass spectrometry, TXRF offers the advantage of determining the sampling depth with the same instrument, so that no assumptions about sputtering rates or auxiliary measurements are necessary. With this method a depth resolution of 2.5 nm is obtained, which is comparable with the best achievable results from other depth profiling methods. Moreover, an additional TXRF scan in a nondestructive mode of operation makes a mutual comparison with the results of the sectioning technique possible. © 1995 American Institute of Physics. View full abstract»

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  • Improved capillary optics applied to microbeam x‐ray fluorescence: Resolution and sensitivity

    Page(s): 24 - 27
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    A new and improved type of x‐ray capillary optics unit (ellipsoidal), is developed, tested, and characterized using a table‐top x‐ray microbeam setup. The beam profiles of the x‐ray beams generated by the 7.5 μm ellipsoidal capillary were constructed from ‘‘knife‐edge’’ scans across the beam. The detection limits for various elements were determined, and the spatial resolution, when the beam was used in scanning mode, was demonstrated. © 1995 American Institute of Physics. View full abstract»

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  • High density polarized hydrogen gas target for storage rings

    Page(s): 28 - 31
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    A target of gaseous polarized hydrogen was formed by injecting polarized hydrogen atoms (produced by Stern–Gerlach spin separation) into a storage cell consisting of a cylindrical tube open at both ends. The target was placed in a storage ring to study the target characteristics (nuclear polarization, target thickness, radiation resistance). A weak transverse guide field (5 G) was applied to define the polarization direction. When atoms in a single hyperfine state were selected, the nuclear polarization of the target was measured to be 0.80±0.02. The areal density of the target under these conditions was (5.5±0.2)×1013 H/cm2, while for two spin states (applicable to experiments in high energy rings where a strong magnetic field can be applied to the target) the target thickness was found to be (8.2±0.3)×1013 H/cm2. The target polarization was unaffected by prolonged exposure of the target to beams up to 1 mA. © 1995 American Institute of Physics. View full abstract»

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  • New type of radial collimator for strain measurements by neutron diffraction

    Page(s): 32 - 37
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    We present a new type of radial collimator made of boron fibers. Coupled with a position sensitive detector system it is optimal for neutron diffraction studies of internal strain measurements. We show the results of the calibration and first test measurements on such a system. The obtained characteristics are excellent and allow a substantial (30) gain factor in data acquisition time. © 1995 American Institute of Physics. View full abstract»

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  • Interferometric measurement of the physical constants of laser dye solvents

    Page(s): 38 - 42
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    The absolute value of refractive index and its variation with temperature of benzene and chloroform at He‐Ne laser wavelength 6328 Å are measured. The measurements are carried out using laser interferometric technique. This technique is based on the shift of interference pattern when rotating the sample in one arm of a newly developed Mach–Zehnder interferometer. The refractive index shows a linear relationship with temperature in the range of interest. The thermal refractive index coefficients of benzene and chloroform are all negative. Applying Maxwell’s theory and Lorentz–Lorenz function, the obtained results are used for calculating the optical permittivity (or dielectric susceptibility) as a function of temperature and many other important related physical constants. © 1995 American Institute of Physics. View full abstract»

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  • Optical distance meter using a short pulse width laser diode and a fast avalanche photodiode

    Page(s): 43 - 47
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    An accurate optical distance meter that features a pulsed laser diode as a light source and two avalanche photodiodes as detectors, is reported. A cascade connection of avalanche transistors drives the laser diode to emit a periodic output pulse of 0.8 ns rise time. The photodiode rise time was found to increase whenever the incident intensity decreased below a certain threshold. Measurement errors caused by this effect were corrected by numerical processing. The optical distance meter yielded a calibration error of 0.5 mm for a white paper target placed 1 m from the laser source. The distance meter was also utilized to profile the bottom of a plastic waterpipe. © 1995 American Institute of Physics. View full abstract»

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  • High‐frequency modulated light source for phase fluorometry and fluorescence lifetime imaging

    Page(s): 48 - 51
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    Phase fluorometry and fluorescence lifetime imaging require a source of exciting light which can be modulated at radiofrequency. This is difficult to achieve with reasonable efficiency using conventional light sources with external modulators such as Pockels cells, while laser sources are limited in wavelength tunability. In this paper a low‐cost and versatile high‐frequency modulated light source is described which is well suited to frequency‐domain fluorescence measurements. The source is a modified deuterium arc lamp which can be driven directly at frequencies up to approximately 130 MHz, and which provides a highly stable source of ultraviolet and visible light. © 1995 American Institute of Physics. View full abstract»

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  • Stopped‐flow time‐resolved extended x‐ray‐absorption fine structure technique for studying reaction dynamics in solution

    Page(s): 52 - 54
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    A microcomputer‐controlled x‐ray absorption spectrometer was built which can measure 1000 ms resolved extended x‐ray‐absorption fine structure for dynamic system of the reaction in solution. Further, we built a new stopped‐flow apparatus suitable for x‐ray absorption spectroscopy in dispersive mode. The spectrometer integrates the x‐ray absorption signals over a time interval (gate time) at any time measured from the time of sample mixing. The gate time depends on the concentration of the sample solution and the x‐ray intensity from x‐ray generator. The raw data on the time resolved‐K‐edge absorption are presented to demonstrate the feasibility of this spectrometer. © 1995 American Institute of Physics. View full abstract»

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  • Laser‐induced surface ionization in a time‐of‐flight mass spectrometer

    Page(s): 55 - 62
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    A laser‐induced ionization scheme based on laser‐metal interaction is described. It is found that when a low power, pulsed UV laser beam is directed to the repeller plate of a Wiley–McLaren time‐of‐flight mass spectrometer (TOFMS), which is held at much higher positive potential than the extraction grid, extensive ionization of gas phase species can take place. For monatomic species such as Ar and Xe, multiply charged ions up to Ar6+ and Xe9+ are obtained. For both aromatic and aliphatic organic molecules, classical electron‐impact‐type mass spectra are observed. Mass resolution is in the range of 300–400, comparable to that obtained using laser‐induced resonant two‐photon ionization (R2PI) in the same linear TOFMS. It is shown that this technique can be quite efficient in ionizing organic species. A detection limit of 5 ng and a linear dynamic range of four orders of magnitude for benzene are demonstrated. While not as sensitive as R2PI, it has a much wider applicability and more uniform ionization efficiency than R2PI. It also appears about 1000 times more sensitive than the incorporation of an electron gun in TOFMS. The technique can be interchanged with R2PI very readily by simply adjusting the position and focus of the laser beam. While the ionization mechanism involved in the technique is currently unknown, some preliminary investigation of the ionization process is reported. It is suspected that photoelectron generation from the plate surface may play some important role in producing the ions detected. © 1995 American Institute of Physics. View full abstract»

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  • Filar ion cyclotron resonance ion trap: Spatially multiplexed dipolar and quadrupolar excitation for simultaneous ion axialization and detection

    Page(s): 63 - 66
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    A novel Fourier transform ion cyclotron resonance ion trap consists of two conventional solid ‘‘end cap’’ electrodes and four ‘‘filar’’ electrodes, each composed of two interdigitated ‘‘combs.’’ The filar trap provides for ion dipolar excitation and ejection, dipolar detection, quadrupolar axialization, and various combinations in a single trap without additional voltage divider circuitry and signal switching between operating modes, because two different functions can be conducted simultaneously by use of two spatially multiplexed electrodes. The filar electrodes produce simulated dipolar and quadrupolar potential fields which are nearly indistinguishable (near the trap center) from those produced by solid electrodes. © 1995 American Institute of Physics. View full abstract»

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  • In situ absolute calibration of a channel electron multiplier for detection of positive ions

    Page(s): 67 - 71
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    A technique has been developed to determine the absolute single particle counting efficiency of a channel electron multiplier (CEM) for positively charged ions at keV energies. The calibration technique is applicable to positive ion detectors in general. Ion beam currents of C2+ were created by charge transfer of C3+ on H2 in the thin target regime. By adjusting the H2 pressure in the beam scattering chamber from 10-10 to 10-6 Torr, C2+ currents could be created either low enough to be detected by the CEM in the particle counting mode or high enough to be measured as a current using the CEM as a Faraday cup. The CEM counting efficiency was determined by comparing the C2+ count rate to the C2+ current, scaling by the change in H2 pressure, and also scaling by the incident C3+ current for each C2+ measurement. This method, which effectively uses the charge transfer cross section as a ‘‘transfer standard,’’ allows the CEM counting efficiency to be determined in situ and to be monitored accurately over extended periods of time. The calibration requires that only the relative, not the absolute, pressure change be known. The technique does not require the value of the charge transfer cross section to be known. The accuracy of the calibration technique for the present results was 10% at a confidence level considered to be equivalent to a statistical 90% confidence level. For the present work, the peak counting efficiency of a Galileo 4039 CEM for 32.5 keV C2+ ions was determined to be 96%. © 1995 American Institute of Physics. View full abstract»

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  • Sub‐eV electron spectroscopy in ion‐atom collisions

    Page(s): 72 - 79
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    A newly designed spectrometer is presented, which is eminently suited for the measurement of electron velocity distributions in the sub‐eV electron energy region. The application of this spectrometer is demonstrated in an ion‐atom collision experiment, using a time‐of‐flight technique. As an example, the low‐energy electron spectrum of 4 keV ionizing H+-H2 collisions is shown. © 1995 American Institute of Physics.   View full abstract»

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  • Self‐calibration of a thinned, backside illuminated charge coupled devices in the soft x‐ray region

    Page(s): 80 - 86
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    A semiempirical method of calibrating a thinned, backside illuminated charge coupled device (CCD) chip in the soft x‐ray region is presented. It is based on determining the thickness of the dead layer self‐consistently using the continuum emission from laser produced plasmas. The CCD camera system was coupled to a transmission grating spectrometer and recorded the spectrally resolved continuum emission from laser irradiated tungsten targets. The thickness of the dead layer was then determined by comparing the experimental spectra with the calculated quantum efficiency for a thinned CCD using a simplified model. In this way the CCD chip was semiempirically calibrated. The accuracy of the calibration in the soft x‐ray range was assessed by comparing the CCD recorded spectra with those recorded by a spectrometer using the absolutely calibrated Kodak 101 photographic plates and a similar transmission grating. Based on this calibration, the CCD sensitivity is deduced to be about two orders of magnitude higher than that of the Kodak plates in this wavelength range. © 1995 American Institute of Physics. View full abstract»

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  • Atomic force microscope using optical heterodyne detection incorporated in an optical microscope

    Page(s): 87 - 90
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    An atomic force microscope has been constructed which enables us to observe sample surfaces through a metallurgical optical microscope. The cantilever deflection is detected by a polarization common‐path interferometer with optical heterodyne technique. The optical system of the interferometer is incorporated in the commercial optical microscope. The common‐path interferometer is rather insensitive to the effects of environmental disturbance such as thermal drift and mechanical vibration. The sample surface and the cantilever are observed by a microscopic objective of ×20. We can adjust the interferometer easily by observing both the cantilever and laser beams. The detection system has a total rms noise of 0.35 Å in a frequency bandwidth of 0.5–200 Hz on a free Si3N4 cantilever of 0.1 N/m spring constant. © 1995 American Institute of Physics. View full abstract»

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  • Low‐temperature scanning tunneling microscope for ballistic electron emission microscopy and spectroscopy

    Page(s): 91 - 96
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    Design details and initial results are presented for a low‐temperature scanning tunneling microscope specifically intended for measurements of ballistic‐carrier transmittance through heterostructures. The basic design is of the Besocke type, modified for ballistic electron emission microscopy and spectroscopy (BEEM). This instrument is the first to acquire BEEM spectra below 77 K. Salient features are (1) operation in a liquid‐helium storage Dewar to below 6 K, (2) a lateral positioning range of 5 mm at low temperature, and (3) lateral drift rate less than 0.2 nm/h at the lowest temperatures. For BEEM spectroscopy, the microscope’s high positional stability allows extended signal‐averaging at a single location on the sample. © 1995 American Institute of Physics. View full abstract»

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  • Very sharp platinum tips for scanning tunneling microscopy

    Page(s): 97 - 100
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    To achieve both high stability for scanning tunneling microscopy (STM) measurements and well‐defined tunnel current localization even on very rough surfaces, we have developed a new electrochemical procedure using CaCl2 etching and H2SO4 micro polishing technique to obtain a very reproducible tip geometry. The mean curvature radius is about 50 Å. The contamination‐free platinum tips are usable for a long time as well in air as in ultrahigh vacuum. The tip quality has been tested by STM measurements on gold (111) surfaces and on liquid‐crystal films. Tips are stable and provide good STM image in far less time than commonly used tips. © 1995 American Institute of Physics. View full abstract»

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  • Phase‐locked noncontact scanning force microscope

    Page(s): 101 - 105
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    A new tip height control system for noncontact scanning force microscope (SFM) utilizing the phase‐lock technology is proposed. Its most extensive feature is that the system is unconditionally stable whereas the conventional control systems have difficulties in stability especially when the tip is at close proximity to the sample surface. In this new system, an oscillator using the cantilever as a mechanical resonator is used as a voltage controlled oscillator (VCO) in a phase‐locked loop. Its output signal phase is locked to a high precision frequency source. The force gradient detected by the cantilever equivalently alters the VCO control voltage, which is detected as a compensational signal of the loop filter output. The phase‐lock technique made it possible to reduce the tip height to an extent which was impossible with the conventional servo technology. Thus this new control technique is expected to be effective in improving the resolution of the noncontact SFM. © 1995 American Institute of Physics. View full abstract»

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  • Radio frequency superconducting parametric transducer for gravitational wave antennae

    Page(s): 106 - 114
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    We report on the design and testing of an ultrasensitive, electromechanical transducer for use on resonant mass gravitational wave antennae. The transducer is a superconducting, radio frequency resonant bridge circuit operating near 200 MHz. We have minimized several important sources of noise in this transducer system. The Johnson noise of the transducer circuit is reduced through using a superconducting niobium stripline circuit and low‐loss insulating materials. At a temperature of 4.2 K we have achieved unloaded electrical quality factors of 200 000. The bridge circuit is balanced by piezoelectric actuators which control the spacing between the proof mass and capacitive segments of the stripline circuit and we have achieved a residual bridge imbalance of 3×10-7. Finally, low noise cryogenically cooled field‐effect transistors are used for the first amplifier stage, enabling us to obtain an amplifier noise level which is 5400 times the quantum limit. The transducer, which has a 0.080 kg proof mass, was affixed to the end of a prototype, resonant bar, gravitational wave antenna with a mass of approximately 100 kg. The primary purpose of this small antenna was to evaluate the transducer, which is designed to be mounted on a much more massive antenna. Our theoretical analysis and measurements of the detector agree and indicate a burst noise temperature of 1.8 K using the 100 kg bar. This corresponds to a gravity wave burst sensitivity of h=1.1×10-16, in terms of relative strain amplitude. With no other improvements, if the transducer mechanically resonant frequency were tuned to and installed on a 2000 kg antenna, the antenna would reach a noise temperature of 1.3 mK, which is equivalent to a gravitational wave burst sensitivity, h≊5.7×10-19. © 1995 American Institute of Physics. View full abstract»

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  • Vertical and horizontal transfer function measurements on a magnetic gas spring

    Page(s): 115 - 119
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    A magnetic gas spring (MGS) has been developed to be the filter element of the super attenuator (SA), the device designed to support the optical components of the gravitational interferometric antenna VIRGO. Measurements have been performed on a MGS in order to study the resonance structure of the attenuation spectra in both the vertical and horizontal directions. Results guarantee an attenuation of at least 40 dB almost everywhere from 10 Hz to 1 kHz. By using experimental data the calculated performances of the SA turn out to be quite adequate for the VIRGO project requirements. © 1995 American Institute of Physics.   View full abstract»

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  • Charge measurement and control for the Gravity Probe B gyroscopes

    Page(s): 120 - 129
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    We describe a technique based on photoemission for controlling the charge of the Gravity Probe B electrostatically suspended gyroscopes, and three methods for measuring this charge. Charging is caused by cosmic radiation in orbit and by enhanced field emission in ground testing. Errors induced by disturbing torques require the potential of the gyroscope to be smaller than 15 mV (15 pC) during the space experiment. The disturbing drift rate produced by measuring and controlling the charge in orbit is smaller than 10-13 deg/h, as compared with the 10-11 deg/h systematic drift rate of the gyroscope. The charge control technique is based on ultraviolet photoemission of electrons from both the gyroscope and a charge control electrode on the gyroscope housing. We demonstrate the effectiveness of this method in ground testing and therefore its suitability for the space experiment. Calculations indicate that heating by absorbed photons is, in the worst case, smaller than 1 nW and thus not a problem for the experiment. The principal charge measurement method is based on the determination of the control effort needed to balance a force modulation applied to the suspension electrodes. This technique is insensitive to pickup from the suspension system and to gyroscope miscentering, and is independent of the gyroscope acceleration. We demonstrate that the force modulation method is suitable for charge monitoring in orbit with an accuracy equal to or better than 4 mV. © 1995 American Institute of Physics. View full abstract»

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  • Doppler‐shifted neutral beam line shape and beam transmission

    Page(s): 130 - 138
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    Analysis of Doppler‐shifted Balmer‐α line emission from the Tokamak Fusion Test Reactor’s (TFTR) neutral beam injection systems has revealed that the line shape, which is a direct measure of the velocity distribution function, is well approximated by the sum of two Gaussians, or, alternatively, by a Lorentzian. For the sum of two Gaussians, the wide‐divergence part of the distribution contains 40% of the beam power and has a divergence five times that of the narrow part. Assuming a narrow 1/e‐divergence of 1.3° (based on fits to the beam shape on the calorimeter), the wide part has a divergence of 6.9°. The entire line shape is also well approximated by a Lorentzian with a half‐maximum divergence of 0.9°. Up to now, most fusion neutral beam modelers have assumed a single Gaussian velocity distribution, at the extraction plane, in each direction perpendicular to beam propagation. This predicts a beam transmission efficiency from the ion source to the calorimeter of 97%. Waterflow calorimetry data, however, yield a transmission efficiency of ∼75%, a value in rough agreement with predictions of the two Gaussian or Lorentzian models presented here. The broad wing of the two Gaussian distribution also accurately predicts the loss in the neutralizer. An additional factor in determining the power density at the surface of beam absorbers is the angle at which the particles arrive. Angles are different for particles emitted from different locations on the ion source. To treat this situation, the average angle of incidence is calculated. For beam loss at the exit of the neutralizer, the average angle of incidence is 2.2°, rather than the 4.95° subtended by the center of the ion source. This average angle of incidence is found to be a function of beam divergence. © 1995 American Institute of Physics. View full abstract»

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  • Far‐infrared laser diagnostics on the HT‐6M tokamak

    Page(s): 139 - 142
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    A multichannel far‐infrared (FIR) hydrogen cyanide (HCN) laser interferometer was developed to measure plasma electron density profile on the HT‐6M tokamak. The structure of the seven‐channel FIR laser interferometer is described. The laser source used in the interferometer was a continuous‐wave glow discharge HCN laser with a cavity length of 3.4 m and power output of about 100 mW at 337 μm. The detection sensitivity was 1/15 fringe with a temporal resolution of 0.1 ms. Experimental results were measured by the seven‐channel FIR HCN laser interferometer with edge Ohmic heating, a pumping limiter, and ion cyclotron resonant heating on the HT‐6M tokamak are reported. © 1995 American Institute of Physics.   View full abstract»

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Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques.

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Editor
Albert T. Macrander
Argonne National Laboratory