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Dec 1996

Volume 67, Issue 12, pp. 4045-4400

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Grid separation oscillator using resonant coaxial cavities for high power multichannel laser

W. D. Bilida, H. J. J. Seguin, and C. E. Capjack

Rev. Sci. Instrum. 67, 4045 (1996); http://dx.doi.org/10.1063/1.1147547 (5 pages) | Cited 1 time

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Resonant cavity techniques have been used to implement a high power source of radio frequency excitation for many parallel laser elements in a simple, compact, and low cost structure. A triode oscillator was designed capable of driving up to 48 independent and dynamic loads by utilizing the unique nature of a resonant cavity to extract multiple outputs via magnetic coupling. Over 25 kW of power has been generated at 80 MHz while driving 8 independent CO2 laser slab geometry gas discharges. © 1996 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
84.30.Ng Oscillators, pulse generators, and function generators
84.30.Jc Power electronics; power supply circuits
42.55.Lt Gas lasers including excimer and metal-vapor lasers

Photoacoustic mapping of the amplification region and characterization of a dye laser amplifier

G. Ramos‐Ortiz and M. Villagrán‐Muniz

Rev. Sci. Instrum. 67, 4050 (1996); http://dx.doi.org/10.1063/1.1147549 (7 pages) | Cited 1 time

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Mapping of the amplification region and full characterization of a dye laser amplifier by means of a photoacoustic technique are presented. The acoustic signals generated in the pumped medium as a consequence of nonradiative transitions are gain dependent. We use the ratio between the acoustic signal measured when the oscillator beam passes through the amplifier, to the acoustic signal when it is blocked, as a figure of merit of an amplifier stage. By using the oscillator beam as a spatial probe of the amplifier gain region, it is possible to map the optically inverted medium, assigning a photoacoustic ratio to each point of the medium. © 1996 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Mv Dye lasers
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators

Fabry–Perot interferometer in Brillouin scattering experiments

Tomasz Błachowicz, Roman Bukowski, and Zygmunt Kleszczewski

Rev. Sci. Instrum. 67, 4057 (1996); http://dx.doi.org/10.1063/1.1147550 (4 pages) | Cited 5 times

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The Fabry–Perot interferometer has become a standard spectroscopic tool in scientific laboratories for the study of Brillouin scattering. This article examines some basic properties of the Fabry–Perot interferometer with the student or beginning user in mind in order to demonstrate why it is especially useful for this application. Single and complex Fabry–Perot systems in use for Brillouin scattering studies are discussed starting from elementary equations to show, in particular, how the half‐width of the transmission function depends upon the instrumental configuration. The primary results are summarized in graphical form. © 1996 American Institute of Physics.
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07.60.Ly Interferometers
42.30.-d Imaging and optical processing
42.65.Es Stimulated Brillouin and Rayleigh scattering

Background reduction in experiments with x‐ray glass capillary optics

P. Engström and C. Riekel

Rev. Sci. Instrum. 67, 4061 (1996); http://dx.doi.org/10.1063/1.1147551 (3 pages) | Cited 2 times

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An analysis of the background at the exit of tapered borosilicate glass capillaries in synchrotron radiation scattering experiments suggests scattering due to short‐range order at larger angles while low‐angle scattering is attributed to phase separation in the glass. Background scattering can be largely suppressed by introducing a pinhole aperture at the exit of the capillary. The lowest background was obtained for a pinhole approaching the size of the exit beam. Background reduction is particularly important for wide‐ and small‐angle scattering experiments on weakly scattering samples like thin polymeric fibers. © 1996 American Institute of Physics.
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07.85.Qe Synchrotron radiation instrumentation
61.05.cf X-ray scattering (including small-angle scattering)
42.70.Ce Glasses, quartz

Fluorescence correlation spectroscopy with traveling interference fringe excitation

Mineyuki Hattori, Hideaki Shimizu, and Hiroshi Yokoyama

Rev. Sci. Instrum. 67, 4064 (1996); http://dx.doi.org/10.1063/1.1147552 (8 pages) | Cited 9 times

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A new improved fluorescence correlation spectroscopy method for determining motional states of particles, fluorescence correlation spectroscopy with traveling interference fringe excitation (FCSTFE), is described. With this method the modulated fluorescence signal from particles excited by an interference fringe moving at constant velocity is detected, and cosine and sine Fourier coefficients at the frequency of the traveling fringe [Fcos(t), Fsin(t)] are recorded. Autocorrelation functions of Fcos(t), Fsin(t), and the square of amplitude [A2(t)=Fcos(t)2+Fsin(t)2] were found to express the motion of the fluorescent particles. The apparatus utilizing a photon counting system was constructed, and the performance of the system was demonstrated by the determination of diffusion coefficients of dispersed fluorescent polystyrene spheres. Features of FCSTFE in particle dynamics evaluation are discussed. © 1996 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
82.70.Kj Emulsions and suspensions

A multioctave coaxially oriented beam‐resonator arrangement Fourier‐transform microwave spectrometer

Jens‐Uwe Grabow, Wolfgang Stahl, and Helmut Dreizler

Rev. Sci. Instrum. 67, 4072 (1996); http://dx.doi.org/10.1063/1.1147553 (13 pages) | Cited 123 times

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The design, performance, and operation of a broadband (3–26.5 GHz) high resolution microwave spectrometer is described. In comparison to previously developed molecular beam Fabry–Perot resonator spectrometers the design presented here implements some significant improvements: a coaxially oriented beam resonator arrangement (COBRA) formed by a confocal pair of mirrors incorporating an electromechanical valve and employing two pairs of microwave antennas, and a multioctave Fourier‐transform microwave (FTMW) instrument providing the pulsed excitation source with microwave pulse phase‐inversion scheme and the low‐noise receiving system employing image‐rejection downconversion with superheterodyne as well as quadrature detection. The entire apparatus, fully automated for scanning operation, covers a frequency range of more than three octaves. The novel design of the FTMW instrument does not require any changes of the spectrometer hardware in order to reach all regions of its spectral range. While operated in high resolution mode the COBRA‐FTMW spectrometer is achieving a linewidth (half‐width at half‐height, HWHH) relative to the molecular emission frequency of better than 10−7 HWHH. The sensitivity and resolution of the spectrometer is demonstrated by several examples. © 1996 American Institute of Physics.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
33.20.Bx Radio-frequency and microwave spectra
07.50.-e Electrical and electronic instruments and components
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

A detailed examination of stimulated pump‐probe measurements of vibrational population relaxation

G. J. Blanchard

Rev. Sci. Instrum. 67, 4085 (1996); http://dx.doi.org/10.1063/1.1147554 (7 pages)

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We have developed and demonstrated a pump‐probe laser spectroscopic scheme to measure ground state vibrational population relaxation. There are two significant advantages to this technique over alternative measurement methods. The first is that the detection sensitivity of the pump‐probe method is limited by the shot noise present on the probe laser and the second is that, because of the manner in which the ground state vibration(s) are populated, it is possible to interrogate T1 processes for degenerate donor–acceptor conditions. We detail in this article the form of the experimental stimulated signal, the effect of the detection scheme used, and the consequences of spontaneous (Boltzmann) population of ground state vibrations. A central conclusion of this work is that, even for small signal limit pump‐probe experiments, absorption, stimulated emission, and spontaneous emission all play important roles in collectively determining the form of the experimental signal. © 1996 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.45.+h Stimulated emission
42.62.Fi Laser spectroscopy

In situ grazing incidence x‐ray diffraction system for clusters deposited on a low‐temperature substrate

Kenji Koga and Harutoshi Takeo

Rev. Sci. Instrum. 67, 4092 (1996); http://dx.doi.org/10.1063/1.1147546 (6 pages) | Cited 7 times

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A grazing‐incidence x‐ray diffraction (GIXRD) system combined with cluster formation and deposition chambers was constructed in order to study structures of clusters deposited on a low‐temperature substrate. Clusters are formed by the vapor condensation method with helium gas in the formation chamber. They are injected into the deposition chamber through a nozzle and deposited on a silicon wafer cooled down to the liquid nitrogen temperature. After deposition, GIXRD measurement is carried out without changing vacuum and temperature conditions (in situ). Using the new apparatus, GIXRD measurements were performed on two different kinds of gold cluster deposits prepared on room‐temperature and low‐temperature substrates. The size distribution of gold clusters used for both preparation conditions was measured to be 15±7.5 Å by the transmission electron microscope observation of gold clusters sparsely deposited on amorphous carbon film. Diffraction pattern from the room‐temperature deposit of gold clusters showed the bulk face‐centered‐cubic (fcc) structure with an average grain size of 42 Å estimated from a peak width, while that from the low‐temperature deposit did not exhibit the simple fcc, but probably the icosahedron‐like structure. The former result is due to coalescence growth among deposited clusters at room temperature, and the latter result suggests that the low‐temperature cluster deposition does not destroy the characteristic structure of free clusters. © 1996 American Institute of Physics.
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61.05.C- X-ray diffraction and scattering
61.46.-w Structure of nanoscale materials
07.85.Jy Diffractometers
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Study of a laser‐heated electron gun

P. K. Roy, A. Moon, K. Mima, S. Nakai, M. Fujita, K. Imasaki, C. Yamanaka, E. Yasuda, T. Watanabe, N. Ohigashi, Y. Okuda, and Y. Tsunawaki

Rev. Sci. Instrum. 67, 4098 (1996); http://dx.doi.org/10.1063/1.1147577 (5 pages) | Cited 5 times

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A method of cathode heating using a laser was studied for an electron gun. In order to observe the practicality of the heating system, the characteristics of the laser‐heated gun with a dispenser and LaB6 thermionic cathodes have been experimentally investigated. The direct laser irradiation is so efficient that the gun is equipped without heat shielding, a cooling system, or an electrical circuit in the gun chamber for cathode heating. Modeling, based on the experimental data, indicates that the cathode temperature is proportional to one‐fourth power of the laser power and that laser power loss and conduction loss of heat in the gun assembly are negligible. An electron beam current density 0.48 A/cm2 was measured with 26 W laser power for a dispenser cathode of 0.06 cm2 emission area. Current density 0.16 A/cm2 with 25 W was recorded for a LaB6 cathode of area 0.12 cm2. Electron beam emittance has been measured by using the typical pepper‐pot technique. It was observed that the growth of electron beam emittance was very small in the laser heating. © 1996 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
41.75.Fr Electron and positron beams
42.62.-b Laser applications
41.85.Ew Particle beam profile, beam intensity

An inline optical electron polarimeter

K. W. Trantham, T. J. Gay, and R. J. Vandiver

Rev. Sci. Instrum. 67, 4103 (1996); http://dx.doi.org/10.1063/1.1147555 (6 pages) | Cited 3 times

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The design and operation of a simple inline optical electron polarimeter is presented. It is based on exchange excitation of ground state neon atoms. The electron polarization is determined from the degree of circular polarization of the subsequent 2p53p 3D3→2p53s 3P2 (6402 Å) fluorescence. This device can characterize both longitudinally and transversely polarized electron beams in a nondestructive fashion, and is inexpensive and easily constructed. © 1996 American Institute of Physics.
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07.60.Fs Polarimeters and ellipsometers
34.80.Dp Atomic excitation and ionization
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment

Effects of frequency and magnetic field scaling on the superconducting electron cyclotron resonance ion source at MSU‐NSCL

S. Gammino, G. Ciavola, R. Harkewicz, K. Harrison, A. Srivastava, and P. Briand

Rev. Sci. Instrum. 67, 4109 (1996); http://dx.doi.org/10.1063/1.1147556 (5 pages) | Cited 14 times

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A series of systematic tests have been carried out on the superconducting electron cyclotron resonance ion source SCECRIS at the Michigan State University National Superconducting Cyclotron Laboratory in order to better understand the role of different parameters which determine the performance of these sources. A relevant part of these tests has been focused on the role of magnetic field and microwave frequency, with the goal of demonstrating the capability of low frequency electron cyclotron resonance ion sources to produce high ion charge states, in spite of their relative low plasma density. This goal can be achieved using a very high magnetic confining field, according to the concept of a high B mode. A comparison of the source performance at 2.45 and 6.4 GHz for different levels of magnetic field is described in this article. © 1996 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams
29.27.Ac Beam injection and extraction
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
07.77.Ka Charged-particle beam sources and detectors
52.50.Dg Plasma sources

Design and tests of the new partially ionized beam source

S. K. Koh, H. G. Jang, W. K. Choi, H.‐J. Jung, S. G. Kondranine, and E. A. Kralkina

Rev. Sci. Instrum. 67, 4114 (1996); http://dx.doi.org/10.1063/1.1147578 (3 pages)

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We developed and evaluated a new partially ionized beam (PIB) source to deposit high quality Cu films. The novelty of the PIB source lies in the fact that the crucible and ionization parts are spaced in one cylindrical shell to make its structure compact and to get a uniform beam profile, but their electric circuits are not separated. In this article, we report the characteristics of the PIB source, such as voltage‐ampere characteristics of the crucible and ionization parts, Cu+ ion beam uniformity with a change of the ionization currents, and deposition rate. © 1996 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Cd Deposition by sputtering

Multichannel source of synthesized ion‐electron flow

A. A. Bizioukov, A. Y. Kashaba, K. N. Sereda, A. Ph. Tseluyko, and N. N. Yunakov

Rev. Sci. Instrum. 67, 4117 (1996); http://dx.doi.org/10.1063/1.1147548 (3 pages) | Cited 2 times

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In this article, we present a multichannel source with cold electrodes generating spatially combined ion and electron beams with homogeneous profile of current density on 100 mm diam. The source was designed on the basis of a modified Penning cell. The anode configuration provides high current efficiency, reaching 50% under certain conditions. The source has two operating modes: ion beam generation and synthesized ion‐electron flow. High current densities 0.5–5 mA/cm2 of ion and electron beams with energies in the range of 0.5–7 keV under low working pressure (1–10)×10−5 Torr are the advantage of this source. © 1996 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
41.85.Ar Particle beam extraction, beam injection
52.50.Dg Plasma sources
52.80.Sm Magnetoactive discharges (e.g., Penning discharges)

A simple current mode preamplifier for electron multipliers with high voltage biased anode

Seong‐Heon Seo, Hong‐Young Chang, and S. K. Kim

Rev. Sci. Instrum. 67, 4120 (1996); http://dx.doi.org/10.1063/1.1147557 (4 pages) | Cited 1 time

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We developed a simple current mode preamplifier for the microchannel plate (MCP) with the anode biased to high voltage. It uses a capacitor to block dc high voltage and measures the MCP current through the capacitor. Then it compensates exactly the distortion caused by the capacitor so the amplifier can measure any length of signals without distortion. It is much less expensive and simpler than using the phosphor screen system to isolate the dc high voltage. We derived a formula for that compensation and implemented it by using an op‐amp’s circuit. It gives an approximate time resolution of 10 μs which is restricted by the op‐amp’s characteristics. So, it may be improved by using fast op‐amp’s. This can also be used for channeltron and other electron multipliers. For the test of the preamplifier, we measured the photoelectron currents induced by the soft x rays radiated from the KT‐1 tokamak of which the pulse length was 20 ms. The data revealed well, without distortion, the time evolution of the line radiation. © 1996 American Institute of Physics.
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29.40.-n Radiation detectors
07.68.+m Photography, photographic instruments; xerography
84.30.Le Amplifiers
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

Steady state behavior of a multipolar plasma device

M. Carrère, L. Chérigier, C. Arnas‐Capeau, G. Bachet, and F. Doveil

Rev. Sci. Instrum. 67, 4124 (1996); http://dx.doi.org/10.1063/1.1147558 (6 pages) | Cited 9 times

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A low pressure discharge plasma, with magnetic multipolar confinement, is produced in a cylindrical ultrahigh vacuum device. The device has been specially designed to allow both moving Langmuir probe measurements and laser induced fluorescence diagnostic for the plasma ions. It is well suited to explore the sheaths region in a bounded plasma and to study wave and turbulence in a laboratory plasma. The main characteristics of the experimental setup and of the produced plasma are described. © 1996 American Institute of Physics.
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52.75.-d Plasma devices
52.55.-s Magnetic confinement and equilibrium
52.70.-m Plasma diagnostic techniques and instrumentation
52.70.Ds Electric and magnetic measurements
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.35.Ra Plasma turbulence
52.40.Hf Plasma-material interactions; boundary layer effects

Use of emissive probes in high pressure plasma

Shiluo Yan, Husain Kamal, Jay Amundson, and Noah Hershkowitz

Rev. Sci. Instrum. 67, 4130 (1996); http://dx.doi.org/10.1063/1.1147559 (8 pages) | Cited 8 times

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The characteristics of emissive probes in unmagnetized high pressure (≤1 Torr) argon and helium plasmas, produced by inductively coupled 13.56 MHz rf power, are studied. A procedure is given for interpreting emissive probe current–voltage (I–V) characteristics. The I–V curves indicate the amplitude of the rf fluctuation of the plasma potential. They also show ionization near the emissive probe when the potential drop between the emissive probe and the plasma potential is more than the ionization potential. Experiments show that when the temperature of the emissive probe wire and/or the neutral pressure is increased, ionization becomes significant. An increase in the local ion density due to the additional ionization was demonstrated by the I–V curves of an emissive probe and a nearby Langmuir probe. A simple procedure is presented for interpreting these results. © 1996 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas

Ultrafast broadband frequency modulation of a continuous wave reflectometry system to measure density profiles on ASDEX Upgrade

A. Silva, M. E. Manso, L. Cupido, M. Albrecht, F. Serra, P. Varela, J. Santos, S. Vergamota, F. Eusébio, J. Fernandes, T. Grossmann, A. Kallenbach, B. Kurzan, C. Loureiro, L. Meneses, et al.

Rev. Sci. Instrum. 67, 4138 (1996); http://dx.doi.org/10.1063/1.1147517 (8 pages) | Cited 34 times

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A reflectometry system has been developed for ASDEX Upgrade to measure the plasma profile from the scrape‐off layer until the bulk plasma, simultaneously at the high and low field sides. Unique features of the system are the ultrafast broadband frequency modulation of a continuous wave using solid state stable hyper abrupt tuned oscillators (down to 10 μs), high and low field side channels and fully remote control operation, via optical fiber links. Due to the special design of the transmission line, with decoupled in going and out going lines and one‐antenna configuration, the system is optimized for reception and spurious reflections are eliminated. The ultrafast operation guarantees that the effect of plasma turbulence is greatly reduced. Both features determine the high performance of the diagnostic. A dedicated data acquisition system handles the large amounts of data generated by the broadband operation. Recent developments include the operation of new channels and an automatic and accurate frequency calibration circuit. Also, advanced digital signal processing techniques were applied to obtain density profiles with high spatial and temporal (20 μs) resolutions under turbulent plasma regions, e.g., the scrape‐off layer. Experimental results are presented showing the great sensitivity of the diagnostic to plasma radial movements and its tolerance to vertical movements of the plasma. Density profiles measured in ELMy regimes illustrate the capabilities of the diagnostic to detect fast profile changes. © 1996 American Institute of Physics.
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52.70.Gw Radio-frequency and microwave measurements
07.05.Hd Data acquisition: hardware and software
52.55.Fa Tokamaks, spherical tokamaks
28.52.Lf Components and instrumentation
07.07.Tw Servo and control equipment; robots

Fast pyroelectric detector for broadband radiated power measurements

C. Côté and A. W. DeSilva

Rev. Sci. Instrum. 67, 4146 (1996); http://dx.doi.org/10.1063/1.1147560 (4 pages) | Cited 3 times

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Basic design requirements are presented for pyroelectric detectors to be used effectively when the radiation source emits part or all of its power in the vacuum ultraviolet range, as is the case for a typical plasma in magnetic confinement fusion research. The difficulty associated with the VUV wavelength range lies in the high photoelectric yield of the associated energetic photons. A relatively inexpensive, commercially available detector was modified to eliminate the spurious currents resulting from photoelectrons. The modifications have little effect on the basic characteristics of the commercial detector (time response, sensitivity, etc). © 1996 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
85.60.Gz Photodetectors (including infrared and CCD detectors)
52.55.Jd Magnetic mirrors, gas dynamic traps

Liquid‐jet target for laser‐plasma soft x‐ray generation

L. Malmqvist, L. Rymell, M. Berglund, and H. M. Hertz

Rev. Sci. Instrum. 67, 4150 (1996); http://dx.doi.org/10.1063/1.1147561 (4 pages) | Cited 26 times

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We describe a new liquid‐target system for low‐debris laser‐plasma soft x‐ray sources. The system is based on a microscopic liquid jet and is experimentally evaluated for 0.7–1 keV proximity lithography and water‐window x‐ray microscopy applications. Compared to an existing liquid‐droplet target, this target system has the same low debris emission, high x‐ray photon flux, and narrow spectral bandwidth. The advantages of the liquid‐jet target include improved x‐ray flux stability, increased range of suitable target liquids, and elimination of the need for temporal synchronization, thereby allowing less complex laser systems to be used. © 1996 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
85.40.Hp Lithography, masks and pattern transfer

Encoding technique for high data compaction in data bases of fusion devices

J. Vega, C. Crémy, E. Sánchez, A. Portas, and S. Dormido

Rev. Sci. Instrum. 67, 4154 (1996); http://dx.doi.org/10.1063/1.1147544 (7 pages) | Cited 4 times

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At present, data requirements of hundreds of Mbytes/discharge are typical in devices such as JET, TFTR, DIII‐D, etc., and these requirements continue to increase. With these rates, the amount of storage required to maintain discharge information is enormous. Compaction techniques are now essential to reduce storage. However, general compression techniques may distort signals, but this is undesirable for fusion diagnostics. We have developed a general technique for data compression which is described here. The technique, which is based on delta compression, does not require an examination of the data as in delayed methods. Delta values are compacted according to general encoding forms which satisfy a prefix code property and which are defined prior to data capture. Several prefix codes, which are bit oriented and which have variable code lengths, have been developed. These encoding methods are independent of the signal analog characteristics and enable one to store undistorted signals. The technique has been applied to databases of the TJ‐I tokamak and the TJ‐IU torsatron. Compaction rates of over 80% with negligible computational effort were achieved. Computer programs were written in ANSI C, thus ensuring portability and easy maintenance. We also present an interpretation, based on information theory, of the high compression rates achieved without signal distortion. © 1996 American Institute of Physics.
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28.52.Lf Components and instrumentation
52.70.-m Plasma diagnostic techniques and instrumentation
07.05.Hd Data acquisition: hardware and software
52.55.Fa Tokamaks, spherical tokamaks

Torsional oscillator magnetometer for high magnetic fields

P. A. Crowell, A. Madouri, M. Specht, G. Chaboussant, D. Mailly, and L. P. Lévy

Rev. Sci. Instrum. 67, 4161 (1996); http://dx.doi.org/10.1063/1.1147562 (6 pages) | Cited 15 times

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We have designed and constructed a torsional oscillator magnetometer for use in magnetic fields up to 25 T. The anisotropic component of the magnetization is detected by measuring the shift in the resonant frequency of the oscillator, which is fabricated from a single‐crystal silicon wafer using micromachining techniques. The frequencies for the oscillators described here are between 100 Hz and 1 kHz and can be measured with a resolution of order 1 part in 108 in a 10 s averaging time, allowing for the detection of magnetic moments of 2×10−11 J/T at 1 T. Our oscillators are optimized for experiments on GaAs‐AlGaAs heterostructures, but the method is suitable for any sample with an anisotropic susceptibility. We have applied the technique to two systems, a quasi‐one‐dimensional spin chain and a two‐dimensional electron gas. © 1996 American Institute of Physics.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
07.10.Cm Micromechanical devices and systems
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Autocalibrating quasistatic M‐H hysteresis loop tracer with negligible drift

V. Franco, J. Ramos‐Martos, and A. Conde

Rev. Sci. Instrum. 67, 4167 (1996); http://dx.doi.org/10.1063/1.1147563 (4 pages) | Cited 12 times

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A computer‐controlled system for measuring M‐H hysteresis loops of soft magnetic materials is described. It overcomes many of the problems associated with these kinds of measurements of low coercivity materials. The combination of ‘‘low drift’’ hardware and measurement procedure makes software correction unnecessary. At every field step, the homemade integrator is reset in order to minimize the drift and to provide a way of separating the sample contribution to the signal from the field contribution and, consequently, to allow M‐H plots. Furthermore, to avoid the residual drift of the hardware, the method of ‘‘two‐way measurement’’ is applied, giving drifts of 0.01% per hour. Results obtained for a FINEMET alloy film annealed at different temperatures are presented, illustrating the ability of the system to measure soft magnetic materials. © 1996 American Institute of Physics.
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07.55.-w Magnetic instruments and components
07.05.Hd Data acquisition: hardware and software
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A linearized Josephson–Fraunhofer magnetometer with high‐temperature Josephson junction

C. Dolabdjian, P. Poupard, V. Martin, C. Gunther, J. F. Hamet, and D. Robbes

Rev. Sci. Instrum. 67, 4171 (1996); http://dx.doi.org/10.1063/1.1147564 (5 pages) | Cited 3 times

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We have fabricated a Josephson–Fraunhofer magnetometer based on the shrinking of the Fraunhofer pattern exhibited by high‐Tc grain boundaries Josephson (GBJ) junctions. It is obtained using flux focuser and GBJ junction directly patterned on a single chip. The device is actively voltage biased and operates in a field locked loop as conventional superconducting quantum interference device systems. The amplitude of the auxiliary modulation field is adjusted to obtain the maximal sensitivity; the coupling between the feedback coil and the flux focuser has been studied to evaluate the magnetometer performances. The system bandwidth is 1 kHz and the measured noise level is 40 pT/√Hz above 10 Hz. The slew rate and the dynamic range of the magnetometer are 2 mT/s and 112 dB (1 Hz bandwidth), respectively. © 1996 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
85.25.Cp Josephson devices

Study of forward characteristics of a cryogenic temperature sensor diode

Mohua Bose and S. B. Ota

Rev. Sci. Instrum. 67, 4176 (1996); http://dx.doi.org/10.1063/1.1147565 (3 pages) | Cited 3 times

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The current dependence of the forward voltage of a cryogenic silicon diode temperature sensor (CRYO Industries of America, Inc.) is reported here in the temperature range 10–300 K. The current values are varied from 10 nA to 0.1 A. The sensitivity of the diode is observed to increase for lower current values in the high temperature range. The rapid increase of the forward voltage at low temperatures is observed to be suppressed considerably by reducing the current. This study helps us to conclude that for all practical purposes such commercial diodes (prescribed for a particular current value of 10 μA) can be operated for a wider range of current values, with suitable calibration data. © 1996 American Institute of Physics.
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07.20.Dt Thermometers
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
85.30.Kk Junction diodes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Design and characterization of a digital control system for the flow through a microporous membrane

C. Molina, A. Arenas, L. Victoria, and J. A. Ibáñez

Rev. Sci. Instrum. 67, 4179 (1996); http://dx.doi.org/10.1063/1.1147566 (6 pages)

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In many scientific and industrial applications the permeating flow through a membrane separating two fluid phases must be kept constant, either because the flow is feeding another system which requires a constant in‐flow, or because membrane fouling is being studied and it is necessary to know what must be done to maintain the flow. We describe a digital proportional‐integral controller which makes it possible to maintain a constant permeating flow through a Nuclepore membrane with 8 μm mean pore radius. © 1996 American Institute of Physics.
Show PACS
47.85.L- Flow control
47.56.+r Flows through porous media
07.05.Dz Control systems
07.07.Tw Servo and control equipment; robots
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