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Dec 1997

Volume 68, Issue 12, pp. 4309-4628

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Fiber Bragg gratings

Andreas Othonos

Rev. Sci. Instrum. 68, 4309 (1997); http://dx.doi.org/10.1063/1.1148392 (33 pages) | Cited 117 times

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Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques (interferometric, phase mask, and point by point) are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed. © 1997 American Institute of Physics.
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42.81.Wg Other fiber-optical devices
42.79.Dj Gratings
42.81.Bm Fabrication, cladding, and splicing

Design of a short-pulse, far-infrared free electron laser with a highly overmoded waveguide

Li Yi Lin and A. F. G. van der Meer

Rev. Sci. Instrum. 68, 4342 (1997); http://dx.doi.org/10.1063/1.1148393 (6 pages) | Cited 3 times

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We report the design of a long wavelength extension to the free electron laser for infrared experiments. A parallel plate is inserted in the resonator to reduce diffraction losses. It will be shown that with a 10 mm gap waveguide, single transverse mode operation can be expected over a wavelength range from 300 down to 40 μm, allowing pulses as short as a few optical cycles to be produced. © 1997 American Institute of Physics.
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41.60.Cr Free-electron lasers
42.60.By Design of specific laser systems

Diagnosis of relativistic electron beams using a free electron laser amplifier

F. Ciocci and G. Dattoli

Rev. Sci. Instrum. 68, 4348 (1997); http://dx.doi.org/10.1063/1.1148394 (3 pages)

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The potential use of a free electron laser (FEL) amplifier as a diagnostic tool for relativistic electron beams is investigated. It is in fact shown that a simple relation exists between electron bunch length, energy spread, and the gain of a FEL resonant amplification. It is also discussed how the beam qualities can be derived from an actual experimental configuration. Finally, the possibility of combining the present methods to other techniques, like nondestructive diagnosis with short undulators, is also analyzed. © 1997 American Institute of Physics.
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41.75.Ht Relativistic electron and positron beams
29.27.Fh Beam characteristics
41.60.Cr Free-electron lasers
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
07.77.Ka Charged-particle beam sources and detectors

Midinfrared free electron laser power delivery through a chalcogenide glass fiber

Kunio Awazu, Seiji Ogino, Akio Nagai, Takio Tomimasu, and Shozo Morimoto

Rev. Sci. Instrum. 68, 4351 (1997); http://dx.doi.org/10.1063/1.1148395 (2 pages) | Cited 11 times

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This article reports on the results of free electron laser (FEL) power transmission measurements through chalcogenide fibers. The FEL power transmission was tested by two types of chalcogenaide NSEG fibers, a normal fiber and a tapered fiber, made by varying the drawing speed from 2 to 17 cm/min. As a result, the tapered NSEG fiber is able to transmit 5–7 μm FEL power with a 10 MW/micropulse without surface damage. Tapered NSEG fibers are useful, therefore, for power transmission to narrow spaces such as the slide glass between the stage and the objective lens in a microscope. © 1997 American Institute of Physics.
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42.81.Dp Propagation, scattering, and losses; solitons
41.60.Cr Free-electron lasers
42.70.Ce Glasses, quartz

A novel scheme of laser interferometer–refractometer with high spatial and temporal resolutions

I. V. Lisitsyn, S. Kohno, and H. Akiyama

Rev. Sci. Instrum. 68, 4353 (1997); http://dx.doi.org/10.1063/1.1148396 (4 pages) | Cited 2 times

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A novel scheme combining interferometer and refractometer for simultaneous plasma density and plasma density gradient measurements is described. The scheme employs a ribbon laser beam obtained from one-dimensional laser beam expansion by a pair of cylindrical lenses. This beam shape allows measurements at several spatial locations simultaneously. The beam deflection measurements give additional important information on the spatial distribution of plasma density gradient in the direction perpendicular to the major axis of the expanded beam. Fast pin photodiodes are used as light detectors for temporal resolution better than 1 ns. The high power (700 mW) of the argon ion laser allows 0.1° phase resolution and simultaneously 0.1 mrad refractional deflection angle resolution. © 1997 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
07.60.Ly Interferometers
07.60.Hv Refractometers and reflectometers
52.25.-b Plasma properties

Wide-dynamic-range digital correlator using field programmable gate arrays

Junji Kinoshita, Midori Matsumoto, and Tadashi Aoki

Rev. Sci. Instrum. 68, 4357 (1997); http://dx.doi.org/10.1063/1.1148391 (2 pages) | Cited 1 time

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A new digital correlator was developed. The one-bit-clipped digital correlator used so far is simple and sensitive enough to detect one photon. The clipping circuits, however, tend to distort the temporal characteristics. In order to alleviate the distortion, we extended the clipping points of counters and multipliers to two bits and three bits, respectively. The novel correlator has the dynamic range ten times wider than that of one-bit-clipped correlator. Here we report the 130 channel correlator that uses seven chips of field programmable gate array. © 1997 American Institute of Physics.
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07.60.Dq Photometers, radiometers, and colorimeters
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
07.68.+m Photography, photographic instruments; xerography

Temperature programmed desorption-mass spectrometer with supersonic molecular beam inlet system

Albert Danon, Ifat Avraham, and Jacob E. Koresh

Rev. Sci. Instrum. 68, 4359 (1997); http://dx.doi.org/10.1063/1.1148397 (5 pages) | Cited 5 times

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A novel atmospheric temperature programmed desorption-mass spectrometer (TPD-MS) device based on supersonic molecular beams (SMB) is demonstrated. The coupling between SMB and TPD-MS enables one to obtain highly sensitive TPD measurements with very fast time response (less than 1 s), that makes it possible to distinguish between desorptions from energetically neighboring sites. Quantitative adsorption measurements of adsorbing gas and vapors could be easily done. High detection sensitivity of 4 ng/s for H2O16 and 100 pg/s for H2O18 is achieved. The high sensitivity TPD measurements are demonstrated by the ability to monitor simultaneous physical adsorption of nitrogen, oxygen, and water on various sites on carbon fibers at room temperature. © 1997 American Institute of Physics.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
07.75.+h Mass spectrometers
37.20.+j Atomic and molecular beam sources and techniques

Construction of a subpicosecond double-beam laser photolysis system utilizing a femtosecond Ti:sapphire oscillator and three Ti:sapphire amplifiers (a regenerative amplifier and two double passed linear amplifiers), and measurements of the transient absorption spectra by a pump-probe method

Toshihiro Nakayama, Yutaka Amijima, Kazuyasu Ibuki, and Kumao Hamanoue

Rev. Sci. Instrum. 68, 4364 (1997); http://dx.doi.org/10.1063/1.1148398 (8 pages) | Cited 27 times

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A double-beam Ti:sapphire laser photolysis system has been constructed for measurements of the subpicosecond transient absorption spectra by a pump-probe method. Although the spectroscopic characteristics tested for the practical availability are satisfactory enough, the transient absorption spectrum thus obtained exhibits an artificial time-dependent spectral change owing to the group velocity dispersion of the probing light pulse. Hence, its wavelength-dependent arrival time to the sample cell is determined utilizing the optical Kerr effect induced in carbon tetrachloride and the true transient absorption spectrum (the corrected spectrum) at a given delay-line setting is calculated by a microcomputer using a great number of uncorrected transient absorption spectra obtained at different delay-line settings. Interestingly, the corrected singlet-singlet absorption band (band C with a lifetime of 0.8 ps) obtained for the lowest excited singlet state of 9-nitroanthracene in cyclohexane really shifts with time. This can be interpreted in terms of the wide wavelength-range superposition of band C and an absorption band which increases and then decreases with rise and decay times of 0.8 and 1.8 ps, respectively; the latter band is ascribed to the absorption of 9-nitrite (or its precursor) or that of a higher excited triplet state of 9-nitroanthracene. By 400 nm biphotonic excitation of the neat solvents (cyclohexane and n-heptane), furthermore, population of their higher excited singlet states with a very short lifetime of 0.4 ps can be seen. © 1997 American Institute of Physics.
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82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
33.80.Be Level crossing and optical pumping
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
07.60.Rd Visible and ultraviolet spectrometers
42.55.Rz Doped-insulator lasers and other solid state lasers

A synchrotron x-ray liquid surface spectrometer

Mark L. Schlossman, Dennis Synal, Yongmin Guan, Mati Meron, Grace Shea-McCarthy, Zhengqing Huang, Anibal Acero, Scott M. Williams, Stuart A. Rice, and P. James Viccaro

Rev. Sci. Instrum. 68, 4372 (1997); http://dx.doi.org/10.1063/1.1148399 (13 pages) | Cited 32 times

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The design of a synchrotron x-ray liquid surface spectrometer at beamline X19C at the National Synchrotron Light Source is described. This spectrometer is capable of performing the full range of x-ray surface scattering techniques. A few examples of measurements made using this spectrometer are presented, including studies of organic monolayers on the surface of water and of the structure of strongly fluctuating oil–microemulsion interfaces. The measurements discussed illustrate the accuracy, resolution, and capabilities of the spectrometer. © 1997 American Institute of Physics.
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07.85.Nc X-ray and γ-ray spectrometers
07.85.Qe Synchrotron radiation instrumentation
61.05.cm X-ray reflectometry (surfaces, interfaces, films)
29.30.Kv X- and γ-ray spectroscopy
68.18.-g Langmuir-Blodgett films on liquids
61.05.cf X-ray scattering (including small-angle scattering)
68.03.-g Gas-liquid and vacuum-liquid interfaces
68.05.-n Liquid-liquid interfaces

A new compact 60 kV Mott polarimeter for spin polarized electron spectroscopy

V. N. Petrov, M. Landolt, M. S. Galaktionov, and B. V. Yushenkov

Rev. Sci. Instrum. 68, 4385 (1997); http://dx.doi.org/10.1063/1.1148400 (5 pages) | Cited 16 times

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A compact 60 kV Mott polarimeter has been constructed, tested, and calibrated especially for the local analysis of surface and two-dimension magnetism by means of electron spectroscopy with spin resolution. The use of construction combining spherical accelerating field with the absence of retarding potential after electron scattering provides low sensitivity of the polarimeter to movements of the analyzed electron beam and changes in its diameter. Special silicon surface-barrier detectors with large electron-optical acceptance provide efficiency ∊ ( ≡ Seff2×I/I0) about ≈ 2.5×10−4. The unique fast electronics allow to work with maximum count rate of detected electrons up to 5×106 counts/s. As a result, there is the possibility to calibrate the polarimeter (to calculate the effective Sherman function Seff) by extrapolation of the measured asymmetry to the high level of discrimination. This instrument is compact, fully UHV compatible and may be used in other fields of solid state physics, atomic physics, and physics of high energies. © 1997 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy
29.40.Wk Solid-state detectors
75.70.Rf Surface magnetism

A new compact electron spin polarimeter with a high efficiency

S. Qiao, A. Kimura, A. Harasawa, M. Sawada, J.-G. Chung, and A. Kakizaki

Rev. Sci. Instrum. 68, 4390 (1997); http://dx.doi.org/10.1063/1.1148401 (6 pages) | Cited 30 times

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We have developed a new compact retarding-potential Mott spin polarimeter and achieved an efficiency of 1.9×10−4 for gold target operating in 25 keV. A novel design of the retarding field electron optics with 0.59 sr collection solid angle for scattered electrons was adopted based on Monte Carlo calculations for the spin-dependent electron scattering process and electron beam ray-tracing calculations. We have combined the new spin polarimeter with an angle-resolved photoelectron spectrometer and measured the spin- and angle-resolved photoelectron spectra and studied the spin-dependent electronic structure of Ni(110) along the mathmath line of its surface Brilluoin zone. © 1997 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Gj Other metals and alloys
73.20.At Surface states, band structure, electron density of states
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Preparation of ultrathin free-standing targets for (e,2e) spectroscopy

Z. Fang, X. Guo, S. Utteridge, S. A. Canney, I. E. McCarthy, M. Vos, and E. Weigold

Rev. Sci. Instrum. 68, 4396 (1997); http://dx.doi.org/10.1063/1.1148402 (8 pages) | Cited 6 times

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We describe in detail the procedures used for the preparation of ultrathin (∼10 nm) free-standing membranes for (e,2e) spectroscopy. Such a thin target is needed to minimize electron multiple scattering before and after an (e,2e) event. The development of a rf plasma source which allows in situ thinning and thickness monitoring is of key importance to the success of the target preparation. Materials (C, Si, Ni, Cu, Al2O3, SiO2, CuO) with different properties and structures are usually prepared in different ways. For insulating targets it is important to have a conducting sublayer to avoid the charging problem. A well prepared target usually has a thin area larger than the (e,2e) beam size ( ∼ 0.2 mm in diameter) and yields high quality (e,2e) data from which the electron energy-momentum density in a chosen direction is determined. Efforts demonstrated in this article indicate that the preparation of ultrathin free-standing films is a challenging area where significant technical development is needed.© 1997 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
79.20.Fv Electron impact: Auger emission
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy
06.60.Ei Sample preparation (including design of sample holders)

Design study and experimental performance of a multistage electron collector

Prabir Kumar Roy, Ahsa Moon, Koichi Ohkubo, Naoya Nakao, Kunioki Mima, Sadao Nakai, Masayuki Fujita, Kazuo Imasaki, Chiyoe Yamanaka, Eisaku Sano, and Yoshiaki Tsunawaki

Rev. Sci. Instrum. 68, 4404 (1997); http://dx.doi.org/10.1063/1.1148403 (5 pages) | Cited 1 time

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A multistage electron collector has been designed for an electron-beam energy recovery system. The electrodes of the collector are cylindrical and partially conical or spiky near the axis in order to maintain a continuous field effect on the beam. The field effect of these electrodes is so efficient that a magnetic field is not necessary between the deceleration and collection gap to confine the beam on the axis. The energy recovery efficiency, 99.8%, of the collector was calculated by using a computer code with about 10 mA beam current and −75 keV. To test the performance of the collector, it has been assembled with a laser-heated electron gun and electrically connected to its power supply. The potentials of each electrode have been provided through a voltage divider of several hundred megaohms. Experimentally, the efficiency obtained was 73%–98% with a beam current of 0.67 mA. © 1997 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
41.85.Qg Particle beam analyzers, beam monitors, and Faraday cups
07.81.+a Electron and ion spectrometers
29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy

Analytical and numerical computation of multipole components of magnetic deflectors

Michal Lenc and Bohumila Lencová

Rev. Sci. Instrum. 68, 4409 (1997); http://dx.doi.org/10.1063/1.1148404 (6 pages) | Cited 1 time

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This article presents an analytical expression of the first, the third, and the fifth harmonic component for axial field of magnetic deflectors made of straight or tapered saddle coils or straight toroidal coils in air. In particular, the expressions for the tapered saddle coils and also for the fifth components for straight saddle and toroidal coils have not been derived so far. The existence of the analytical expressions for the simple but important problems of magnetic deflectors in free space is quite advantageous for the check of the correct mesh layout for the more general problems. The axial field functions are compared with those computed with the first order finite element method for the same geometry, with very good agreement of the results. © 1997 American Institute of Physics.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
07.55.Db Generation of magnetic fields; magnets
02.70.Dh Finite-element and Galerkin methods
84.32.Hh Inductors and coils; wiring

Gas-discharge neutralizer for ion-beam system

A. A. Bizyukov, A. Y. Kashaba, and K. N. Sereda

Rev. Sci. Instrum. 68, 4415 (1997); http://dx.doi.org/10.1063/1.1148405 (3 pages)

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The design and operation of a gas-discharge neutralizer of positive ion beams is presented. It is based on the discharge with crossed electric and magnetic fields initiated by the ion beam, which travels through the device, without an additional energy source. Depending on the pressure, there are two types of the discharge inside the neutralizer: high-voltage (at a low pressure p<3×10−4 Torr) and magnetron (at a high pressure p>3×10−4 Torr). In the high-voltage regime, the ion beam is partially neutralized. Full ion beam compensation is achieved in the magnetron regime. © 1997 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
41.75.Ak Positive-ion beams
29.25.Ni Ion sources: positive and negative
52.80.-s Electric discharges

A complex probe for measurements of turbulence in the edge of magnetically confined plasmas

R. M. Castro, M. V. A. P. Heller, R. P. da Silva, I. L. Caldas, F. T. Degasperi, and I. C. Nascimento

Rev. Sci. Instrum. 68, 4418 (1997); http://dx.doi.org/10.1063/1.1148406 (6 pages)

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To improve the turbulence characterization and the estimation of the transport processes at the plasma edge, we designed and installed, in the Brazilian tokamak (TBR), a complex probe that consisted of five single Langmuir probes, a four-channel triple probe, and magnetic probes. In this work, we describe in detail this diagnostic system and present experimental examples of simultaneously measured plasma parameters and electrostatic and magnetic turbulent fluctuations in the TBR tokamak. This procedure permits to investigate any coupling between these two kinds of oscillations. Furthermore, our results confirmed that corrections due to electron temperature fluctuations are relevant for turbulence characterization. © 1997 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.35.Ra Plasma turbulence
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects

Double window configuration as a low cost microwave waveguide window for plasma applications

R. Baskaran

Rev. Sci. Instrum. 68, 4424 (1997); http://dx.doi.org/10.1063/1.1148407 (3 pages) | Cited 3 times

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Waveguide windows are major components of a transmission line used in microwave plasma devices. The function of the waveguide window is to provide vacuum isolation of the source side from the plasma chamber while transmitting microwaves with minimum attenuation. Commonly a single thin dielectric plate is sandwiched between a choke type flange and a flat flange and is used as a waveguide window. To arrive at a better window configuration in terms of the low power reflection coefficient, the voltage standing wave ratio calculation is carried out for different window configurations (single window and double window) and for various window thicknesses. It is found that the power reflection is the minimum in the case of double window configuration. The minimum power reflection is as low as 0.8% for a combination of alumina and a quartz plate each of 1 cm thickness in the double window configuration. Also, it is more advantageous to use radial microwave coupling than axial coupling in order to increase the life time of the microwave waveguide window. © 1997 American Institute of Physics.
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52.75.-d Plasma devices
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
84.40.Az Waveguides, transmission lines, striplines
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

A nondisturbing electric-field sensor using piezoelectric and converse piezoelectric resonances

Yongkwan Lee, Ilryong Kim, and Soonchil Lee

Rev. Sci. Instrum. 68, 4427 (1997); http://dx.doi.org/10.1063/1.1148408 (4 pages) | Cited 5 times

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An electric-field sensor was developed using both piezoelectric and converse piezoelectric resonances. Composed of no metallic parts, this probe minimizes field disturbance. The most distinguishing feature of this probe is that a signal is transmitted neither electrically nor optically, but mechanically. To demonstrate the field sensing capability of this probe, we measured both the capacitive and inductive fields inside empty and plasma-filled solenoidal coils. The result shows that the capacitive field is dominant in an empty solenoid, although it is almost completely shielded by inductively excited plasma. © 1997 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
43.38.Fx Piezoelectric and ferroelectric transducers
84.32.Hh Inductors and coils; wiring
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Effect of broadband wave number and frequency spectra on E×B particle flux in plasmas

T. P. Crowley

Rev. Sci. Instrum. 68, 4431 (1997); http://dx.doi.org/10.1063/1.1148409 (3 pages) | Cited 1 time

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The effect of a broadband wave number (k) and frequency (ω) spectrum S(k,ω), on particle flux due to electrostatic fluctuations in a plasma is examined. Effect of the broadband spectrum on density-potential coherence is also calculated. Particle flux results are compared with a standard quasilinear transport estimate that has been used to interpret heavy ion beam probe and Langmuir probe measurements in fusion plasmas. Situations in which the quasilinear estimate is probably inaccurate are illustrated, including edge shear layer measurements and interior measurements from the TEXT tokamak. © 1997 American Institute of Physics.
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52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
02.70.Hm Spectral methods
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects

Application of a Si-diode detector for fusion product measurements in ASDEX Upgrade

W. Ullrich, H.-S. Bosch, and F. Hoenen

Rev. Sci. Instrum. 68, 4434 (1997); http://dx.doi.org/10.1063/1.1148410 (5 pages) | Cited 1 time

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The efficient confinement of the energetic charged fusion products and the complete transfer of their kinetic energy to the plasma is of great importance for the realization of a fusion reactor which will depend on alpha-particle heating. In todays fusion experiments with deuterium plasmas, this aspect can be investigated using the 1 MeV tritons from the d(d,p)t reaction. The slowing down behavior of these tritons can be studied by measuring the 14 MeV neutrons from the t(d,α)n reaction (triton burnup). At ASDEX Upgrade a time-resolved diagnostic based on a silicon barrier detector has been installed to measure the time evolution of the 14 MeV neutron rate. Using the Si(n,p)Al and Si (n,α)Mg reactions the high energy neutrons, with an energy above the 6 MeV threshold, are converted to charged particles directly inside the semiconductor diode. The complete functionality of the detector system is demonstrated by the successful measurement of the complex spectrum of the charged reaction products in silicon triggered by fusion neutrons during plasma discharges. As an integral component of this diagnostic a time dependent burnup code based on classical slowing-down theory has been developed for the use at ASDEX Upgrade to analyze the complex time evolution of the 14 MeV neutron rate. First measurements are compared to the results of the code. A new application for such detectors is proposed, as in conjunction with the materials of the tokamak structure it can be operated simultaneously as an in situ activation system. © 1997 American Institute of Physics.
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28.52.Lf Components and instrumentation
29.40.Wk Solid-state detectors
52.70.Nc Particle measurements
52.55.Fa Tokamaks, spherical tokamaks
29.85.-c Computer data analysis

The electron cyclotron absorption diagnostic at the Rijnhuizen tokamak project

J. F. M. van Gelder, H. S. Miedema, A. J. H. Donné, A. A. M. Oomens, and F. C. Schüller

Rev. Sci. Instrum. 68, 4439 (1997); http://dx.doi.org/10.1063/1.1148411 (9 pages) | Cited 3 times

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A new 20-channel electron cyclotron absorption diagnostic has been developed at the Rijnhuizen tokamak project. It is the first time the electron pressure profile in a tokamak plasma can be measured directly with a time resolution of 1 ms. The diagnostic measures simultaneously the emission and absorption of the second harmonic electron cyclotron frequencies. Microwaves are injected from the high field side and detected at the low field side in the equatorial midplane. The transmitted power is measured after a single pass through the plasma column. The absorption measurements are complicated by nonresonant losses: refraction of the injected microwaves (losses up to 100%), and scattering of microwaves by density fluctuations (losses 2%–3%). A fast algorithm has been developed to obtain a quantitative measure for these nonresonant losses. This calculation method is based on a parametrization of the experimental data. Combining the electron cyclotron absorption (ECA) measurements and the parametrization provides a reliable tool for determining the optical depth, the electron temperature, and the electron pressure. A good agreement was found between pressure and temperature profiles, measured with ECA and other diagnostics. © 1997 American Institute of Physics.
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52.70.Gw Radio-frequency and microwave measurements
52.55.Fa Tokamaks, spherical tokamaks
52.25.Kn Thermodynamics of plasmas
52.25.Tx Emission, absorption, and scattering of particles
07.05.Kf Data analysis: algorithms and implementation; data management

New extruder-based deuterium feed system for centrifuge pellet injection

S. K. Combs and C. R. Foust

Rev. Sci. Instrum. 68, 4448 (1997); http://dx.doi.org/10.1063/1.1148412 (10 pages) | Cited 3 times

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The pellet injection systems for the next-generation fusion devices (such as the International Thermonuclear Experimental Reactor) and future fusion reactors will have to provide deuterium-tritium fueling for much longer pulse lengths (up to ≈ 1000 s) than present applications (typically limited to less than several seconds). Thus, a prototype pellet feed system for centrifuge pellet injection has been developed and used in long-pulse (>100 s) tests at the Oak Ridge National Laboratory (ORNL). The new apparatus has two key components: (1) a cryogenic deuterium extruder and (2) an electromagnetic pellet punch mechanism. For maximum testing flexibility, the prototype is equipped with several other active components that allow remote adjustments, including precise positioning of the punch and the capability to index through eight different pellet lengths. The new feed system was designed to mate with an existing centrifuge accelerator facility at ORNL, and experiments in the facility were carried out to document the performance and reliability of the new feed system. With 2.3-mm-diam deuterium pellets and a catenary-shaped accelerator ( ≈ 1.2 m diam), the prototype feed system was found to be capable of placing up to ≈ 90% of the punched pellets in the proper time/space window for pickup and acceleration by the high-speed rotating ( ≈ 50 Hz) arbor. For these operating parameters, the pellet nominal speed was ≈ 430 m/s, and maximum pellet feed rates of 10 pellets/s and greater were tested. In this article the equipment is briefly described, and the experimental test results are summarized. Also, issues affecting overall pellet delivery efficiency are discussed. © 1997 American Institute of Physics.
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28.52.Cx Fueling, heating and ignition
28.52.Fa Materials
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Maximum entropy digital signal processing for acoustic Doppler imaging

F. Wright

Rev. Sci. Instrum. 68, 4458 (1997); http://dx.doi.org/10.1063/1.1148413 (4 pages)

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A maximum-entropy algorithm is developed for real time estimation of the power spectrum mean frequency of a Doppler shifted probe. This technique is compared with a covariance argument approximation and performance is given in terms of noise immunity, measurement bias, and accuracy. Estimator evaluation is made from numerical results with a computer simulated signal having a Gaussian spectral density. The maximum-entropy and covariance argument algorithms are implemented on a digital signal processing microprocessor (Analog Devices ADSP2181) for comparison. The maximum entropy technique demonstrates substantial improvement over covariance processing with respect to noise immunity and exhibits no bias in the presence of band limited noise. The maximum-entropy algorithm can be implemented, without any post-processing required, using the ADSP2181 on typical acoustic Doppler signals in the frequency range between 150 and 1200 kHz by frequency down conversion to a fundamental Nyquist interval of 4 kHz. © 1997 American Institute of Physics.
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43.60.+d Acoustic signal processing
05.70.Ce Thermodynamic functions and equations of state
02.50.-r Probability theory, stochastic processes, and statistics
02.60.Cb Numerical simulation; solution of equations
93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
93.85.Bc Computational methods and data processing, data acquisition and storage

Acoustical measurement of the trapping constant of porous materials

Alexis Debray, Jean F. Allard, Walter Lauriks, and Luc Kelders

Rev. Sci. Instrum. 68, 4462 (1997); http://dx.doi.org/10.1063/1.1148414 (3 pages) | Cited 3 times

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A simple method of measuring the trapping constant of porous materials saturated by air is presented. The trapping constant is evaluated from acoustical measurements of the imaginary part of the compressibility of the saturating air at low frequencies. Measurements performed on random packings of spheres are compared with predictions obtained from numerical simulations. Conversely, the connection between the behavior of the compressibility and a well defined physical parameter provides new information about the efficiency of porous sound absorbing materials at low frequencies. © 1997 American Institute of Physics.
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43.58.+z Acoustical measurements and instrumentation
43.50.+y Noise: its effects and control
83.85.Jn Viscosity measurements
47.56.+r Flows through porous media

Study on the temperature sensing capability of a light-emitting diode

Y. B. Acharya and P. D. Vyavahare

Rev. Sci. Instrum. 68, 4465 (1997); http://dx.doi.org/10.1063/1.1148415 (3 pages) | Cited 5 times

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A study on the temperature sensing capability of a light-emitting diode (LED) has been made. Dependence of I–V characteristics as a function of temperature is used as a temperature sensing mechanism. It is found that the temperature voltage characteristics of a GaP LED are quite linear from 77 to 533 K. The measured sensitivity of the diode is 5.31 mV/K at 1 pA and is 2.34 mV/K at 0.1 mA. Since the reverse saturation current of LED is less than fempto-ampere range, it is possible to operate the thermometer at low currents, as compared to silicon or germanium diode thermometers, which reduce power dissipation in the device. It has been possible to extend the temperature range to higher value due to large value of band gap for LEDs. © 1997 American Institute of Physics.
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07.20.Dt Thermometers
85.60.Jb Light-emitting devices
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