bluuebunny/crossref_metadata_2025 huggingface dataset:
Simplified large current crowbar switch using thyristors
Authors: Yang J. G. , Choi J. W. , Choi J. H. , Chang H. Y. , Choi D. I. , Bengtson Roger D.
Published: July 2002

We demonstrate a large current power crowbar switch using thyristors without complex snubber circuits. Current sharing was obtained by selecting circuit elements for uniform impedance of parallel switches and varistors were used for voltage sharing between series elements.
New determination method of resonance and antiresonance frequencies of a piezoelectric resonator
Authors: Kim Jong Sung , Yu Insuk
Published: July 2002

A new detection scheme of resonance and antiresonance frequencies of piezoelectric resonators by utilizing an inductive pulse detection method is developed. This method is applied to a disk piezoelectric resonator and advantages over the conventional ones are noticed.
A fast-response microthermocouple
Authors: Beckman P. , Roy R. P. , Whitfield K. , Hasan A.
Published: July 2002

A fast-response chromel-alumel (and chromel-constantan) microthermocouple is described and its dynamic characteristics are measured. The microthermocouple features a microdisk junction 0.08 mm in diameter and 2.5 μm thick. Its time constant in turbulent flow of liquid Refrigerant-113 (a poor heat conductor) is measured to be ∼4.6 ms. This time constant was reduced to ∼3.4 ms with a phase-lead compensation circuit. It was possible to distinguish between vapor and liquid phase temperatures in turbulent subcooled boiling flow of Refrigerant-113 with the compensated microthermocouple.
An arc discharge hydrogen atom source
Authors: Samano E. C. , Carr W. E. , Seidl M. , Lee Brian S.
Published: July 2002

A magnetically confined thermal electric arc gas heater of easy construction, handling, and maintenance has been designed, built, and tested as a suitable source of heat for dissociating hydrogen molecules. The plasma species in the gas discharge region are assumed to satisfy local thermodynamic equilibrium conditions. The average beam kinetic energy is determined to be 1.5 eV, leading to an arc temperature of approximately 8700 K; the dissociation rate is 0.5 atoms per molecule and the total atom beam intensity in the forward direction is 1018 atoms/sr s. This novel atom source has been successfully ignited and operated with pure hydrogen during several hours of continuous performance, maintaining its characteristics and overcoming some of the difficulties previously found by researchers using other arc sources. The hyperthermal hydrogen atom beam obtained from this source is identified by MoO3 chemical detectors, and analyzed and characterized by three different calorimetric sensors, Ni, Ta, and Teflon. The experimental results obtained with this dissociator agree with those published in the literature.
Count rate performance of spectrometers for fusion neutrons
Authors: Källne J. , Gorini G.
Published: July 2002

The count rate capability of high-resolution neutron spectrometers for fusion plasmas is discussed. In particular, the question of the intrinsic rate limitations in neutron time-of-flight (TOF) spectrometers is assessed quantitatively for two design approaches where the proton recoils from n+H scatterings are detected with in-beam and out-of-beam detectors. It is found that the count rate capability limit lies in the range 50–400 kHz for TOF depending on approach. Comparison is made with other types of neutron spectrometers for fusion experiments. It is shown, for the first time, that neutron spectrometers fall into distinct categories depending on the underlying detection methods and that this information can be used for assessing capability limits of neutron spectrometry as a diagnostic for fusion plasmas.
Fast pyrobolometers for measurements of plasma heat fluxes and radiation losses in the Madison symmetric torus reversed field pinch
Authors: Fiksel G. , Frank J. , Holly D.
Published: July 2002

Two types of fast bolometers are described for the plasma energy transport study in the Madison symmetric torus plasma confinement device. Both types use pyrocrystals of LiTaO3 or LiNbO3 as the sensors. One type is used for measurements of the radiated heat losses and is situated at the vacuum shell inner surface. Another type is insertable in the plasma and measures the plasma particle heat flux. The frequency response of the bolometers is measured to be in the 150–200 kHz range. The range of the measured power fluxes is 0.1 W/cm2–10 kW/cm2 and can be adjusted by changing the size of the entrance aperture. The lower limit is determined by the amplifier noise and the frequency bandwidth, the higher limit by destruction of the bolometer sensor.
A broadband method for the measurement of the surface impedance of thin films at microwave frequencies
Authors: Booth J. C. , Wu Dong Ho , Anlage Steven M.
Published: July 2002

We present a new technique to measure the complex surface impedance of the mixed state of superconducting thin films over the broad frequency range 45 MHz–20 GHz. The surface impedance is extracted from measurements of the complex reflection coefficient made on the film using a vector network analyzer. The technique takes advantage of a special geometry in which the self-fields from currents flowing in the film are everywhere parallel to the film surface, making it an ideal configuration in which to study vortex dynamics in superconductors. The broadband nature of the measurement system allows us to explore a region of magnetic field–temperature–frequency parameter space of superconductors previously inaccessible with other measurement techniques. The power of the technique is illustrated by measurements on thin films of the high temperature superconductor YBa2Cu3O7−δ.
Indium distribution in InGaAs quantum wires observed with the scanning tunneling microscope
Authors: Pfister M. , Johnson M. B. , Alvarado S. F. , Salemink H. W. M. , Marti U. , Martin D. , Morier-Genoud F. , Reinhart F. K.
Published: July 2002

The incorporation of In in the growth of crescent-shaped In0.12Ga0.88As quantum wires embedded in (AlAs)4(GaAs)8 superlattice barriers is studied in atomic detail using cross-sectional scanning tunneling microscopy. It is found that the In distribution in both the surface and the first subsurface layer can be atomically resolved in the empty- and filled-state images, respectively. Strong In segregation is seen at the InGaAs/GaAs interfaces, but neither an expected enhancement of the In concentration at the center of the quantum wire compared to the planar quantum well nor In clustering beyond the statistical expectation is observed.
Ion beam of dielectrics in the pulsed ion source with explosive emission
Authors: Korenev S.
Published: July 2002

The results of the latest experiments on a study of pulsed ion source with explosive emission (PISEE) for forming ions of dielectrics materials are considered in this report. Planar and coaxial vacuum diodes were used in the experiments. The high voltage Arkad’ev–Marx type generator, source of ion supply, had the following main parameters: voltage 300–450 kV; and a pulse duration of 300 ns. The anode plasma initiator had a special dielectric coating which determined the kind of ions. Questions of stable work of PISEE are discussed.
Identification of cesium effects on enhancement of H− production in a volume negative ion source
Authors: Fukumasa Osamu , Tanebe Tomoaki , Naitou Hiroshi
Published: July 2002

Effects of cesium vapor injection on H− production in a tandem source are studied theoretically and parametrically as a function of different surface processes. Model calculation is done by solving a set of particle balance equations in steady-state hydrogen discharge plasmas. By including H− surface production processes caused by H atoms or positive hydrogen ions, enhancement of H− production observed experimentally is reproduced in the model.
The Quadrumafios electron cyclotron resonance ion source: Presentation and analysis of the results (abstract)a)
Authors: Girard A. , Briand P. , Gaudart G. , Klein J. P. , Bourg F. , Debernardi J. , Mathonnet J. M. , Melin G. , Su Y.
Published: July 2002

The Quadrumafios electron cyclotron resonance ion source (ECRIS) has been especially designed to permit physical studies of the plasma; this paper describes the source itself (which has been operated at 10 GHz in a first step), its preliminary performances, and the different diagnostics involved, which mainly concern the electron population [electron cyclotron emission (ECE), x rays, diamagnetism, microwave interferometer, and electron analyzer]. The results are presented and discussed: There is of course a close relationship between the parameters of the plasma and the performances of the source; this point will be discussed in the article.
Micro-Pirani vacuum gauge
Authors: Weng Ping Kuo , Shie Jin-Shown
Published: July 2002

A Pirani vacuum sensor has been fabricated by the silicon micromachining technique. A square glass membrane was formed on (100) silicon substrate with a platinum-film resistor coated. The membrane is suspended by its four leads extended to the corners of an etched cavity. This structure can provide both low thermal loss through leads to the substrate and large active area for gaseous heat conduction. It thus can be used as a highly sensitive vacuum sensor. The fabricated sensor has shown a linear response of pressure from 8×10−5 to 6 Torr with constant-temperature operation. It is found that the low-pressure limit of the vacuum sensor was caused by the noise of the instrument used in the experiment. A new terminology called ‘‘noise equivalent pressure’’ thus is definable due to this finding. The physical limit of the noise equivalent pressure is analyzed. Optimization of the device structure and the noise equivalent pressure are also discussed in detail. A new method of ambient-temperature compensation is also proposed and analyzed here.
Effect of electrode material on measured ion energy distributions in radio-frequency discharges
Authors: Olthoff J. K. , Van Brunt R. J. , Radovanov S. B.
Published: July 2002

Evidence is presented for a significant influence of electrode surface material and condition on the measurement of the kinetic energies of ions sampled from discharges through an orifice in the electrode. Significant differences in ion energy shifts and/or discrimination of low-energy ions are found using aluminum and stainless-steel electrodes in a radio-frequency (rf) discharge cell. It is argued that the observed differences in energy shifts may be attributable in part to differences in charging of oxide layers on the electrode surface around the sampling orifice.
Thermal imaging by atomic force microscopy using thermocouple cantilever probes
Authors: Majumdar A. , Lai J. , Chandrachood M. , Nakabeppu O. , Wu Y. , Shi Z.
Published: July 2002

Thermocouple cantilever probes are used in the atomic force microscope (AFM) to simultaneously obtain thermal and topographical images of surfaces with submicrometer scale spatial resolution. Three designs of thermocouple AFM probes and the thermal images obtained by each of them are presented here. Experiments show that the dominant mechanism for sample-probe heat transfer is gas conduction. If probes are not properly designed, this could lead to image distortion and loss of temperature and spatial resolution. The steady state probe behavior is dominated by the gas thermal conductivity whereas the transient effects are dominated by the thermal mass of the probe. Thermal images of single transistors show their thermal characteristics under different biasing conditions. In addition, hot spots created by short-circuit defects within a transistor can be located by this technique. Efforts are underway to improve the spatial resolution from 0.4 to 0.05 μm by careful probe design. The results suggest that this can be achieved when the size of the thermal sensor at the tip of an AFM cantilever probe is of the order of the tip radius.
Beamline standard component designs for the Advanced Photon Source
Authors: Shu D. , Barraza J. , Brite C. , Chang J. , Sanchez T. , Tcheskidov V. , Kuzay T. M.
Published: July 2002

The Advanced Photon Source (APS) has initiated a design standardization and modularization activity for the APS synchrotron radiation beamline components. These standard components are included in components library, subcomponents library, and experimental station library. This paper briefly describes these standard components using both technical specifications and sideview drawings.
New feedback mechanism for reducing timing jitter between pulses from two synchronously pumped mode-locked lasers
Authors: Okamoto Hiromi , Tasumi Mitsuo
Published: July 2002

We report a new feedback system for reducing timing jitter between optical pulses from two synchronously pumped mode-locked lasers (SPL1 and 2) pumped by common pulses from a mode-locked laser. The beam from SPL1 is divided into two parts, and one of which is optically delayed from the other. Both of these parts are mixed with the beam from SPL2 to generate two sum-frequency beams. The intensity difference between the two sum-frequency beams serves as a measure of the relative timing of pulses from the two lasers. This intensity difference is used as an error signal for the feedback loop. Timing jitter between pulses from SPL1 and SPL2 having an autocorrelation function with a full-width at half-maximum of ≊3 ps was reduced from ≊7 ps (feedback off) to less than 3 ps (feedback on).
A novel method for product identification in complex surface reactions using infrared reflection absorption spectroscopy
Authors: Weldon M. K. , Friend C. M.
Published: July 2002

We report the use of infrared spectroscopy to unambiguously identify the gaseous reaction products evolved during the course of a surface reaction under ultrahigh vacuum conditions. The apparatus consists of two independent, liquid-nitrogen-cooled samples; one is used to trap the gaseous products generated by reaction on the surface of interest. The trapped products are subsequently identified using surface infrared spectroscopy. We demonstrate the utility of this product trapping infrared reflection absorption spectroscopy technique, for the separation of isomers of butene, which are indistinguishable using conventional mass spectrometry, as well as the identification of radical species, such as ⋅CH3, which are important in diamond growth.
Development of a microwave ion source for negative oxygen ion beam production
Authors: Tanaka M. , Miyake K. , Sakudo N. , Kobayashi K. , Ohkawa H.
Published: July 2002

A volume production type microwave negative ion source has been developed for negative ion beam processes such as ion implantation and ion beam deposition, etc. In order to increase efficiency of negative oxygen ion production, we employed a double plasma cell system in which two plasma cells were connected to each other. A high density primary plasma was generated in the first plasma cell with 2.45 GHz microwave power and negative ions were effectively generated in the second plasma cell. A filter magnetic field of about 0.1 T was applied on the second plasma cell to prevent diffusion of high energy electrons from the first plasma cell. Oxygen negative ion beams were generated by this method and the maximum oxygen (O−) ion current of 142 μA (current density: 325 μA/cm2) was extracted continuously from the ion source at an extraction voltage of 30 kV and a microwave power of 500 W. This value was three orders larger than that obtained by a single plasma cell system without the filter magnetic field. Molecular oxygen ions (O−2 and O−3) were also obtained at percentages of about 20% and 2% of the major O− ion intensity.
Neutron penumbral imaging of inertial confinement fusion targets at Phébus (abstract)a)
Authors: Delage O. , Garconnet J-P. , Schirmann D. , Rouyer A.
Published: July 2002

First 14 MeV neutron images of imploded microballoons have been obtained on the Phebus laser facility at CEL-V in 1992 [Garconnet et al. Laser Part Beams 11, 3 (1994)]. The sizes of the neutron source have been measured by using a coded-aperture imaging system and a scintillator array as a detector. The threshold of the experimental setup was typically 2×1010 neutrons/shot. 600–800 μm source sizes in direct drive experiments have been measured with a 130 μm two-point resolution. In 1993 we improved the sensitivity of the camera by increasing the light collection efficiency. It can now work at a neutron yield as small as a few 108. Thanks to this improvement some images in indirect drive experiments have been recorded in the range 3⋅108–5⋅109 with a 56 μm two-point resolution. Wiener filter, homomorphic Wiener filter, and Nugent’s ‘‘comb filter’’ methods have been used and compared to deconvolve the penumbral images. Design of the camera and numerical method performances will be discussed.
Versatile TV system for PBX-M plasma control
Authors: Kugel H. W. , Gettelfinger G. , Semler J. , Thorsland E. , Timberlake J.
Published: July 2002

In advanced tokamak research involving complex magnetic geometries, midplane visible plasma TV images can indicate the need for tokamak control corrections not evident from other diagnostics. Suitable midplane viewports are often unavailable. The PBX-M plasma TV system uses four tangential midplane vacuum viewports. One tangential vacuum viewport is on a standard re-entrant midplane port flange. The other three vacuum viewports are tangentially aligned along the inside vessel wall and connected to port flanges 40 cm from the midplane via 60-cm-long re-entrant bellows. Fiber optic bundles transmit images from the re-entrant viewports through the off-midplane ports and out to TV cameras positioned beyond the TF coils. The VCR recorded images from each discharge were used to obtain information not available from other diagnostics.
Filar ion cyclotron resonance ion trap: Spatially multiplexed dipolar and quadrupolar excitation for simultaneous ion axialization and detection
Authors: Guan Shenheng , Marshall Alan G.
Published: July 2002

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.
Development of rugged corner cube detectors for the TEXT-U FIR interferometer
Authors: Hallock G. A. , Gartman M. L. , Ling H.
Published: July 2002

The corner cube mixers originally developed for the TEXT-U far-infrared interferometer were susceptible to damage by tokamak radiation. The source of the damage has been traced to intense ωpe bursts emitted by the tokamak during start-up. We have determined that this radiation was coupled into the detector through a small gap in the original design. An electromagnetic model has been used to calculate the electric-field distribution within the gap. Results are consistent with the expected power in a burst.
High-frequency modulated light source for phase fluorometry and fluorescence lifetime imaging
Authors: Morgan C. G. , Mitchell A. C. , Peacock N. , Murray J. G.
Published: July 2002

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.
The JET diagnostic fast central acquisition and trigger system (abstract)
Authors: Edwards A. W. , Blackler K.
Published: July 2002

Most plasma physics diagnostics sample at a fixed frequency that is normally matched to available memory limits. This technique is not appropriate for long pulse machines such as JET where sampling frequencies of hundreds of kHz are required to diagnose very fast events. As a result of work using real-time event selection within the previous JET soft x-ray diagnostic, a single data acquisition and event triggering system for all suitable fast diagnostics, the fast central acquisition and trigger system (Fast CATS), has been developed for JET. The front-end analog-to-digital conversion (ADC) part samples all channels at 250 kHz, with a 100 kHz pass band and a stop band of 125 kHz. The back-end data collection system is based around Texas Instruments TMS320C40 microprocessors. Within this system, two levels of trigger algorithms are able to evaluate data. The first level typically analyzes data on a per diagnostic and individual channel basis. The second level looks at the data from one or more diagnostics in a window around the time of interest flagged by the first level system. Selection criteria defined by the diagnosticians are then imposed on the results from the second level to decide whether that data should be kept. The use of such a system involving intelligent real time trigger algorithms and fast data analysis will improve both the quantity and quality of JET diagnostic data, while providing valuable input to the design of data acquisition systems for very long pulse machines such as ITER. This paper will give an overview of the various elements of this new system. In addition, first results from this system following the restart of JET operation will be presented.
Laser-induced surface ionization in a time-of-flight mass spectrometer
Authors: Schriemer David C. , Li Liang
Published: July 2002

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.
Magnetic field mapping system on the H-1 heliac (abstract)a)
Authors: Shats M. G. , Rudakov D. L. , Blackwell B. D. , Sharp L. E. , Fedyanin O. I.
Published: July 2002

The H-1 heliac recently brought into operation is a medium-sized 3-field-period heliac with major radius R0=1 m, plasma mean minor radius 〈a〉≤0.2 m and a wide range of rotational transforms 0.6≤■(0)≤2.0. Electron beam mapping of the vacuum magnetic field was performed using new type of a fluorescent target (movable fluorescent rod array having a transparency about 98%). Up to 150–200 of toroidal transits were observed at each electron gun position. The spatial resolution of the system was about 3 mm. Electron collector probes were used for monitoring the positions of the magnetic surfaces in different toroidal field periods. Visible paths of the electron beam due to the excitation of the background gas (p×10−4 Torr) were used for identification of the toroidal transit numbers. This newly developed method gives an accuracy in measurement of the rotational transform of about 1.5%. Experimental surfaces and measured ■ profiles show very good agreement with the computer model results.
A new cell design for off-axis amplification of ultrashort dye lasers which uses total internal reflection
Authors: Bultmann T. , Bingemann D. , Ernsting N. P. , Schwarzer D. , Nikowa L.
Published: July 2002

A new cell design for off-axis amplification of femtosecond dye lasers which uses total internal reflection is reported. Compared to the conventional on-axis configuration, these amplifiers produce less amplified spontaneous emission in the far field and maintain the input beam profile.
Local plasma radiation loss rate determination in tokamaks and stellarators
Authors: Navarro A. P. , Ochando M. A. , Medina F. , Van Milligen B. P.
Published: July 2002

A modified tomography technique was developed to provide, from two radiation detector arrays covering an entire plasma cross section at a fixed toroidal angle, the local distribution of the time rate of change of the radiated power. The radiated power is the least unambiguously measured of all the components involved in plasma thermal equilibrium and its time evolution could be the most indicative of any perturbation of such equilibrium. The tomography technique has been checked by using simulated thermal perturbations, assuming a 1D transport model for the resulting transport. Experimental setups are presented for the TJ-I tokamak and TJ-IU stellarator.
Steady state behavior of a multipolar plasma device
Authors: Carrère M. , Chérigier L. , Arnas-Capeau C. , Bachet G. , Doveil F.
Published: July 2002

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.
Repeating pneumatic pipe-gun for plasma fueling
Authors: Viniar I. , Sudo S.
Published: July 2002

A pellet injector of the repeating pneumatic pipe-gun type has been designed for plasma fueling applications. Its use reduces the time for pellet formation by an in situ technique from 2 to 3 min to 2–10 s. The basic idea of the proposed approach to pellet formation is to melt prefrozen solid fuel and to admit it through a porous unit into a barrel for refreezing. The injector provides for a continuous injection of an unlimited number of pellets. Over 250 hydrogen and deuterium pellets of 3 mm diameter and 3–10 mm in length were accelerated to 1.2 km/s at a rate of 1 pellet per 10–34 s by manually controlled injector operation. An automatically controlled multishot pellet injector (>10 barrels) is capable of providing a continuous and reliable fueling of large fusion devices such as the large helical device and the International Thermonuclear Experimental Reactor (ITER).
Complete recrystallization of amorphous silicon carbide layers by ion irradiation
Authors: Heera V. , Kögler R. , Skorupa W. , Stoemenos J.
Published: July 2002

Ion-beam-induced recrystallization of amorphous surface layers on single-crystalline silicon carbide substrates (6H–SiC) has been investigated at temperatures of 500 and 1050 °C by cross-sectional transmission electron microscopy and Rutherford backscattering spectrometry and channeling. It is shown, that ion irradiation substantially reduces the onset temperature of both the epitaxial layer regrowth and the random nucleation of crystalline grains. Two recrystallization regimes have been found. At 500 °C ion-beam-induced random nucleation (IBIRN) of crystalline grains strongly competes with ion-beam-induced epitaxial crystallization (IBIEC) and polycrystalline material stops the epitaxial regrowth front in an early stage. At a temperature of 1050 °C IBIEC dominates over IBIRN and a complete, but disturbed epitaxial regrowth is obtained.
Quantized positioning of x-ray interferometers
Authors: Bergamin A. , Cavagnero G. , Mana G.
Published: July 2002

The article demonstrates the feasibility of quantized positioning and moving scanning x-ray interferometers by feedback of traveling fringes. Two new features, feedback and equilibrium quantization, combine to yield accurate positioning and movement by successive transitions between equilibrium positions. In contrast with feedforward positioning and movement, piezoelectric linearity and stability are not subjected to strict conditions. In preliminary experiments, the performances of an x-ray interferometer were greatly improved and servo-movements up to 0.4 μm were achieved and tracked with picometer resolution.
Compact, low power polymer-based optical correlator
Authors: Vacar D. , Heeger A. J. , Volodin B. , Kippelen B. , Peyghambarian N.
Published: July 2002

A low cost, low power compact optical correlator is demonstrated. It operates interchangeably in the matched-filter or joint-transform configurations. The active medium is a high diffraction efficiency photorefractive host–guest polymer system. Successful image correlation has been achieved.
Design considerations for an electrobalance microforce sensor
Authors: Peterson I. R.
Published: July 2002

The design of two microforce sensors using the electrobalance principle and based on commercially available galvanometer units is described in detail. A plausible form for the open-loop frequency response to be expected from optical detection of the position of the meter arm is derived by analyzing the dynamics of a pivoted beam. The Nyquist criterion for stability of the feedback circuit necessary to maintain force balance over a specified range of mechanical loads is considered in the light of ease of manufacture and alignment. With both units, it was relatively easy to achieve zero static compliance and a frequency response of approximately 100 Hz with no resonant behavior. Practical aspects of friction, component variation, measurement noise, and temperature stability are discussed.
A stable scanning tunneling microscope designed for investigations of organic thin films in air
Authors: Sasaki A. , Iwata F. , Katsumata A. , Akiyama T. , Fujiyasu H.
Published: July 2002

A new and stable scanning tunneling microscope (STM) system has been constructed for the investigation of thin organic films in air. The STM unit is made of Macor, which is machinable ceramic and has a small thermal expansion coefficient and a high mechanical stiffness. Three-dimensional coarse position adjustment (within 3 μm) is carried out using five stacked piezoelectric transducers (PZTs). A cross-type configuration is used to prevent the thermal effect of the x- and y-direction displacement mechanism. In order to achieve high resolution, x-, y-, and z-direction displacements are performed using a tube-type PZT. The z direction of the tube PZT has a high mechanical resonant frequency of 24.4 kHz. Therefore, this STM unit is mechanically rigid, and allows stable operation under mechanical disturbances (sound and mechanical vibration). Moreover, this STM unit can be controlled for 24 h or longer by using an ordinary operational amplifier, because thermal effects are compensated. The STM system can also be used to obtain information on the spatially resolved local tunneling barrier height, which is sensitive to the chemical structure of the sample. The capabilities of this newly designed STM are demonstrated with experiments investigating the morphology and tunneling barrier height of stearic acid thin films on indium-tin-oxide substrates.
Recent results from tokamak divertor plasma measurements
Authors: Allen S. L.
Published: July 2002

New diagnostics have been developed to address key divertor physics questions, including: target plate heat flux reduction by radiation, basic edge transport issues, and plasma wall interactions (PWIs) such as erosion. A system of diagnostics measures the target plate heat flux (imaging ir thermography) and particle flux (probes, pressure and Penning gauges, and visible emission arrays). Recently, Te, ne, and Pe (electron pressure) have been measured in two-dimensions (2D) with divertor Thomson Scattering. During radiative divertor operation Te is less than 2 eV, indicating that new atomic processes are important. Langmuir probes measure higher Te in some cases. In addition, the measured Pe near the separatrix at the target plate is lower than the midplane pressure, implying radial momentum transport. Bolometer arrays, inverted with reconstruction algorithms, provide the two-dimensional core and divertor radiation profiles. Spectroscopic measurements identify the radiating species and provide information on impurity transport; both absolute chordal measurements and tomographic reconstructions of images are used. Either intrinsic carbon or an inert species (e.g., injected Ne) are usually observed, and absolute particle inventories are obtained. Computer codes are both benchmarked with the experimental data and provide important consistency checks. Several techniques are used to measure fundamental plasma transport and fluctuations, including probes and reflectometry. PWI issues are studied with in situ coupons and insertable samples (DiMES). Representative divertor results from DIII-D with references to results on other tokamaks will be presented.
An ultrahigh vacuum scanning tunneling microscope for in situ studies of thin-film growth
Authors: Witt Ch. , Mick U. , Bode M. , Wiesendanger R.
Published: July 2002

A new ultrahigh vacuum (UHV) scanning tunneling microscope design has been developed and optimized for in situ investigations of thin-film growth. The basic concept of the microscope is to retract the sample by means of the coarse positioning motor under an angle of 30° with respect to the piezotube scanner. This geometric arrangement allows normal film deposition and excludes any interaction between the evaporation beam and the tip. The instrument has the capability of regaining a particular microscopic location on the sample surface with an accuracy of less than 100 nm posterior to a sample displacement of more than 20 mm. Sequences of images of a spot during homoepitaxial growth of Cr on a Cr(100) single-crystal substrate have been obtained.
Degraded noise characteristics of submicrometer area field effect transistors subjected to plasma etching and Fowler–Nordheim stress
Authors: Martin Scott T. , Li G. P. , Worley Eugene , White Joe
Published: July 2002

The effects of reactive ion etching (RIE) and Fowler–Nordheim (FN) gate current stresses upon both the 1/fγ and random telegraph signal (RTS) noise characteristics of submicrometer gate area metal oxide semiconductor field-effect transistors has been analyzed. While control devices exhibit the Lorentzian noise spectra and discrete switching behavior attributable to single oxide defects, the first layer metal antenna devices exhibit degraded RTSs and near ideal 1/f noise characteristics. An evolution of this 1/f behavior has been reproduced in control devices by subjecting them to a series of UV illuminated FN gate current stresses. Results of this study suggest that multiple oxide traps with a distribution in time constants are generated during RIE and that the amount of oxide degradation generated during plasma etching may be more substantial than that produced during plasma ashing.
Comparisons of a charge coupled device and a microchannel plate detector for Doppler spectroscopy
Authors: Hawkes N. C.
Published: July 2002

Modern charge-coupled-device (CCD) detectors can achieve peak quantum efficiencies of 90%, compared with less than 10% for the photocathode of an electron multiplier. We report on laboratory tests of examples of these two detector technologies to evaluate their relative performance for precision Doppler spectroscopy of laboratory plasmas. The tests reveal that the accuracy of the Doppler width and shift measurements improves with the square root of the photoelectron flux, and thus as the square root of the detector quantum efficiency. An analytic estimate of the performance of these two types of detectors confirms the square root dependence on photoelectron flux but also highlights the importance of other noise sources that could be important under different conditions. The gain of the electron multiplier system can be reduced to the level of 10 photon-electrons per ADC count before there is any reduction in the accuracy of the estimation of fitted parameters.
A three axis parallel drive microrobot
Authors: Kirton Robert S. , Nielsen Poul M. F.
Published: July 2002

In this article we present a three axis parallel drive microrobot. The robot consists of three linear actuators rigidly positioned in a plane with their translational axes arranged in parallel. Each actuator is connected to one apex of a low mass rigid tetrahedral frame by a four axis elastic hinge. Movement of each of the three linear actuators results in displacements of the corresponding hinged apices and, hence, the rigid tetrahedral frame. The fourth apex acts as the working tip which may be positioned anywhere within a workspace determined by the geometry of the robot and the displacement range of the actuators. When the actuator displacement is small compared to the dimensions of the frame the relationship between the displacement of the three actuators and the position of the working tip is well defined, being one to one and only mildly nonlinear (1% nonlinearity for 1.5 mm actuator displacement on an 80 mm frame). A microrobot has been constructed with a workspace measuring 3 mm axially and 5.65 mm transverse to the robot axis. Below 100 Hz the working tip displacement is limited to 3 mm peak-to-peak in the axial direction and 5.65 mm peak-to-peak transverse to the axis. Above 100 Hz the working tip performance is acceleration limited with maximum displacement being inversely proportional to the square of the driving frequency, falling to 120 μm peak-to-peak in the axial direction at 500 Hz.
Use of Langmuir probes in a weakly ionized, steady-state plasma with strong magnetic field
Authors: Batani D. , Alba S. , Lombardi P. , Galassi A.
Published: July 2002

This article describes the use of Langmuir probes to measure plasma parameters in low density, low temperature plasmas with a strong applied magnetic field. The experiment has been performed at the Physics Department of Milan’s University on the steady-state toroidal machine “Thorello.” Results have been analyzed by taking into account instrumental and ionic sheath effects. Finally, experimental results have been compared with direct measurements of the electron distribution function in Thorello.
High-brightness source for ion and electron beams (invited)
Authors: Kalbitzer S. , Knoblauch A.
Published: July 2002

By controlled formation of nanoprotrusions on single-crystal tips of tungsten and iridium extremely bright beams of both ions and electrons were obtained. Specific brightness values range up to 1 TA/cm2 srd eV which are considerably higher than those of previous source systems for charged particle emission. The physical mechanisms involved in the generation of these supertips will be outlined. The basic source properties were used to estimate the limiting image size and the obtainable target current-densities. Some of the most important applications of ion and electron beams are considered for materials modification and analysis.
An intense Hall-type ion source for satellite propulsion
Authors: Guerrini G. , Michaut C. , Bacal M. , Vesselovzorov A. N. , Pogorelov A. A.
Published: July 2002

The design improvements of future plasma thrusters require the investigation of the physical phenomena occurring during the thruster operation. We have investigated a small, Hall-type thruster (or stationary plasma thruster). The different currents and the thrust of the thruster will be reported. Plasma parameters have been measured with Langmuir probes located outside the thruster. Finally, an electrostatic ion energy analyzer located in the plume has permitted the determination of the ion energy distribution function.
Vacuum arc ion and plasma source Raduga 5 for materials treatment
Authors: Ryabchikov A. I. , Stepanov I. B. , Dektjarev S. V. , Sergeev O. V.
Published: July 2002

This article describes a new modification of high current ion and plasma source Raduga 5. A dc vacuum arc is used to generate plasma. Generation of accelerated ion beams is realized in the Raduga 5 in a repetitively pulsed mode with the pulse repetition rate up to 200 pps, the pulse duration up to 400 μs and the accelerating voltage up to 50 kV. To clean the vacuum arc plasma from the microparticle fraction of the products of the explosive cathode emission of the arc evaporator a new version of a straight-line plasma filter is used. This article describes a new version of the accelerating diode which works under conditions of high thermal loads with a continuous metal plasma flow and repetitively pulsed formation of an accelerated ion beams. A simultaneous generation of a metal plasma flow and pulse beams of accelerated ions in the Raduga 5 source ensures realization of the technologies of an ion assisted metal plasma deposition, ion implantation under ion sputtering compensation by metal plasma deposition and ion implantation. The experimental data on different technological regimes of the source are presented in this article. Potential areas of the perspective application of the ion and plasma source Raduga 5 of ion and ion-plasma treatment of different materials are discussed.
Status of 2.45 GHz compact National Institute of Radiological Sciences electron cyclotron resonance ion source
Authors: Muramatsu M. , Kitagawa A. , Sato S. , Tashiro K. , Yamada S. , Shibuya S. , Hattori T.
Published: July 2002

A 2.45 GHz compact National Institute of Radiological Sciences electron cyclotron resonance (NIRS-ECR) ion source has been developed for heavy ion medical accelerator in Chiba at NIRS. A new ECR source is expected to produce C2+ ions of more than 160 eμA for the high-energy heavy-ion cancer treatment. An ECR-type ion source is adopted because of its excellent characteristics of long lifetime and easy operation. The compact ECR ion source is 15 cm in diameter, 20 cm in length, and about 20 kg in weight. A set of permanent magnets was adopted to generate both the axial mirror and the radial sextupole fields. Several gas materials, He, CO2, CH4, N2, and Ne, have been tested. The present performance for C2+ ions, however, is 15 eμA and far below the medical requirements. The estimated vacuum in the plasma chamber is around 5.0×10−5 Torr. A much better vacuum pressure is desired to produce C2+ ions of more than 100 eμA. The ECR plasma, however, cannot be kept stable under such a high vacuum pressure. As another method to get the stable plasma, the different microwave injection was tested with a microwave antenna.
Ion source development at GSI
Authors: Spädtke P. , Bossler J. , Emig H. , Leible K. D. , Mühle C. , Reich H. , Schulte H. , Tinschert K.
Published: July 2002

Different ion sources are used at GSI to match the requirements for specific tasks at the accelerator. At the standard injector a Penning ionization gauge ion source is used (design ion U10+, m/q<24, 1 emA). Further development of this source is mainly aiming at an increase of the extractable currents and an increase of the lifetime of the source. The new injector produces the beam by means of an electron cyclotron resonance source (Caprice-type). Here the design ion is U28+, m/q<8.5, 5 eμA. Clearly, the oven technology is our main development goal. In addition we are trying to improve the extraction flexibility by a moveable accel–decel system. For our high current project ion sources are required which are capable to deliver a beam of several mA even for heavy ions. Design ion here is U4+, m/q<65, 15 emA. For that application two different types of ion source are used: the multicusp ion sources “cold or hot reflex discharge ion source” and “multicusp ion source” for gaseous ions and the MEVVA source for metal beams.
Application of capillary optics to neutron radiography
Authors: Podurets K. M. , Mildner D. F. R. , Sharov V. A.
Published: July 2002

We propose two neutron radiographic techniques that make use of the converging beam from a tapered monolithic lens. The first is a focusing technique that enables one to obtain an image of a given cross section within an object. The second technique is neutron radiography that uses a beam emanating from a near point source. Both methods provide an improvement in spatial resolution for neutron radiography.
Optical high voltage measurement using Pockels microsingle crystal
Authors: Santos Josemir Coelho , Taplamacioglu Muslum Cengiz , Hidaka Kunihiko
Published: July 2002

A new optical high voltage sensor using a Pockels microsingle crystal in a longitudinal modulation arrangement is presented. A prototype of the sensor is assembled and shows an advantage of directly measuring voltage levels up to 50 kV without any potential divider in a wide frequency bandwidth of direct current to 116 MHz. In conventional Pockels sensors, acoustic resonance driven by piezoelectric effect introduces oscillatory components to signals obtained from measurements of lightning impulse voltages. In the new sensor, the measured signal is free from the oscillatory components. An accuracy of 1.9% in good agreement with predicted values is obtained from the lightning impulse voltage measurement.
Vacuum arc plasma transport through a magnetic duct with a biased electrode at the outer wall
Authors: Zhang T. , Tang B. Y. , Chen Q. C. , Zeng Z. M. , Chu P. K. , Bilek M. M. M. , Brown I. G.
Published: July 2002

Metal plasma formed by a vacuum arc plasma source can be passed through a toroidal-section magnetic duct for the filtering of macroparticles from the plasma stream. In order to maximize the plasma transport efficiency of the filter the duct wall should be biased, typically to a positive voltage of about 10–20 V. In some cases it is not convenient to bias the duct, for example if the duct wall is part of the grounded vacuum system. However, a positively biased electrode inserted into the duct along its outer major circumference can serve a similar purpose. In this article, we describe our results confirming and quantifying this effect. We also show the parametric dependence of the duct transport on the experimental variables.