bluuebunny/crossref_metadata_2025 huggingface dataset:
Target diagnostics for intense lithium ion hohlraum experiments on Particle Beam Fusion Accelerator II
Authors: Leeper R. J. , Bailey J. E. , Carlson A. L. , Chandler G. A. , Derzon M. S. , Dukart R. J. , Hebron D. E. , Hunter J. A. , Mix L. P. , Moats A. R. , Nash T. J. , Olson W. R. , Rockett P. D. , Ruiz C. L. , Torres J. A. , Wenger D. F. , Olsen R. W. , Barber T. L. , Lake P. W. , Schmidlapp F. A.
Published: July 2002

A review of the diagnostics used at Sandia National Laboratories to measure the parameters of intense lithium ion-beam hohlraum target experiments on Particle Beam Fusion Accelerator II will be presented. This diagnostic package contains an extensive suite of x-ray spectral and imaging diagnostics that enable measurements of target temperature and x-ray output. The x-ray diagnostics include time-integrated and time-resolved pinhole cameras, energy-resolved one-dimensional streaked imaging diagnostics, time-integrated and time-resolved grazing incidence spectrographs, a transmission grating spectrograph, an elliptical crystal spectrograph, a bolometer array, an 11- element x-ray diode array, and an 11-element PIN diode detector array. The incident Li beam symmetry and an estimate of incident Li beam power density can be measured from ion beam-induced characteristic x-ray line emission and neutron emission.
Stopped-flow time-resolved extended x-ray-absorption fine structure technique for studying reaction dynamics in solution
Authors: Yoshida Noboru , Nagamura Toshihiko
Published: July 2002

A microcomputer-controlled x-ray absorption spectrometer was built which can measure 1000 ms resolved extended x-ray-absorption fine structure for dynamic system of the reaction in solution. Further, we built a new stopped-flow apparatus suitable for x-ray absorption spectroscopy in dispersive mode. The spectrometer integrates the x-ray absorption signals over a time interval (gate time) at any time measured from the time of sample mixing. The gate time depends on the concentration of the sample solution and the x-ray intensity from x-ray generator. The raw data on the time resolved-K-edge absorption are presented to demonstrate the feasibility of this spectrometer.
High-sensitivity, high-resolution measurements of radiated power on TEXT-U
Authors: Wen Yizhi , Bravenec R. V.
Published: July 2002

Investigations of a possible radiation drive of edge turbulence in tokamaks require sensitive radiated power measurements having high temporal and spatial resolution. A commercially available 16-element X–UV-enhanced photodiode array having essentially 100% quantum efficiency from ∼25 to ≥6 keV is used. The frequency response is presently limited by the amplifiers to ∼50 kHz, although the ultimate response is expected to be much higher (≳200 kHz). Each element’s view is ∼0.4 cm wide along the major radius at the plasma midplane while the view of the entire array is ∼6.3 cm wide and is scannable over the entire plasma cross section. The details of the system as well as observations of fine spatial structures and fluctuations undetectable by conventional bolometers are presented.
Diagnosing plasma conditions in light ion beam fusion experiments using inner-shell x-ray line emission (abstract)a)
Authors: MacFarlane J. J. , Wang P. , Bailey J. , Mehlhorn T. , Dukart R.
Published: July 2002

Kα emission spectroscopy is an important diagnostic technique used for plasmas created in intense light ion beam experiments.b),c) Emission lines can be produced as 2p electrons drop down to fill 1s vacancies created by the ion beam. Bailey et al.b) reported the first spectroscopic measurements of Kα x-ray satellites in intense proton beam experiments on PBFA-II at Sandia. Kα emission spectra have also recently been observed in intense Li-beam experiments on PBFA-II.d) Two approaches are used to analyze time-integrated x-ray spectra. In the first, CRE calculations are performed to compute synthetic time-integrated spectra using plasma conditions predicted from radiation-hydrodynamic simulations. In the second approach, plasma conditions are deduced from Kα satellite line intensity ratios measured from the highest ionization stages observed in the experiments. Results will be presented from our analysis of recent PBFA-II x-ray spectra.
Quadrature polarimetry for plasma Faraday rotation measurements
Authors: Howard John
Published: July 2002

A quadrature polarimeter for measurement of plasma magnetic field and electron densities is described. The polarization ellipse tilt angle is encoded as a relative phase shift between orthogonally polarized beams. This phase can be recovered using standard quadrature interferometric methods. The results from a benchtop experiment are presented.
Electron temperature measurements from optically gray third harmonic ECE in DIII-D (abstract)a)
Authors: Austin M. E. , Ellis R. F. , James R. A. , Luce T. C.
Published: July 2002

The electron cyclotron emission spectrum on DIII-D is measured using an absolutely calibrated Michelson interferometer. During high performance discharges, electron densities above 9×1013 cm−3 preclude determination of the electron temperature from the second harmonic ECE. Under these conditions the third harmonic X mode is generally optically gray (0.4<τ<3.0) and can be used to determine Te by correcting the emission intensity for optical thickness. Overlap of the central third harmonic frequencies with optically thick inside-edge second harmonic frequencies on DIII-D allows a particularly simple formalism for determining the correction to the emission. To check the accuracy of the method, the Te values derived from the third harmonic can be compared to those from the second for discharges where it is not cutoff. These comparisons are presented along with an evaluation of various sources of error associated with calculations of the optical depth and the radiation transport.
A spectroscopic method to directly measure nonthermal velocity fluctuations (abstract)
Authors: Zurro B. , Vega J. , Burgos C. , Van Milligen B. P.
Published: July 2002

A spectroscopic method to directly measure the nonthermal velocity fluctuations is being studied in the TJ-I tokamak. The method is based on converting velocity in intensity fluctuations by subtracting the signals received at two symmetric positions of a spectral emission line. This is accomplished by means of a multichannel detector in which the channels respond to the line intensity at different wavelengths and positions within a single spectral line. A multichannel plate photomultiplier, with an anode split in 8×8 parts, is optically coupled by means of an anamorphic optical system, to the focal plane of a 1 m spectrometer where the image of a spectral line is formed. Some individual anodes are grouped to configurate four acquisition channels which are fled into four current amplifiers. The 100 kHz bandwidth signals are stored in a digital oscilloscope connected to a VAX computer, where the signals are processed. A simple simulation allows us to relate the differential signal between symmetrical channels to velocity in cases where the radial extension of the emitting ion is comparable to the radial correlation length of the turbulence causing the velocity fluctuations. The influence of the detection statistics on the measurement is analyzed. Preliminary results obtained in the TJ-I tokamak, using this system, will be presented.
Computer control and data acquisition of the heavy ion beam probe (abstract)
Authors: Demers D. R. , Schoch P. M. , Crowley T. P. , Ouroua A.
Published: July 2002

The heavy ion beam probe (HIBP) on TEXT-upgrade and the vertical test stand (VTS) at Rensselaer are to be operated from a virtual control panel using a graphical language interfacea). The system will monitor and control over eighty signals, as well as acquire data using mouse and keyboard inputs. The computer interface utilizes a DEC 5000/240 workstation, two color monitors, SCSI to fiber optic link, and CAMAC crate. Long term goals include remote experimental monitoring and control, and feedback control. The status and visuals of the computer control system and results of implementation on the VTS will be presented.
Sawtooth studies with q-profile measurements on TFTR (abstract)a)
Authors: Levinton F. M. , Batha S. H. , Yamada M. , Zakharov L. , Zarnstorff M. C.
Published: July 2002

The q profile plays a key role for plasma equilibrium and theories of MHD instabilities. With the development of the motional Stark effect (MSE) diagnostic,b) accurate q(r,t) profiles have been measured and utilized for equilibrium and stability analysis. Data have been obtained for several conditions on TFTR including L mode, supershot, current ramps, noninductive current drive, and high βp. Sawtoothing discharges on TFTR have q(0) well below one, and it remains below one throughout the evolution of the sawtooth cycle. This is in contradiction with the widely believed Kadomtsev model. It has also been found that stabilization of sawteeth can be achieved with q(0)<1. The criteria for stabilization have been compared to several theoretical models such as resistive, ideal, and two-fluid MHD. The ω* stabilization from the two-fluid MHD model agrees well with the data from TFTR.
Uncertainty propagation in q and current profiles derived from motional Stark effect polarimetry on TFTR (abstract)a)
Authors: Batha S. H. , Levinton F. M. , Bell M. G. , Wieland R. M. , Hirschman S. P.
Published: July 2002

The magnetic-field pitch-angle profile, γp(R)≡arctan(Bpol/Btor), is measured on the TFTR tokamak using a motional Stark effect (MSE) polarimeter. Measured profiles are converted to q profiles with the equilibrium code vmec. Uncertainties in the q profile due to uncertainties in the γp(R), magnetics, and kinetic measurements are quantified. Subsequent uncertainties in the vmec-calculated profiles of current density and shear, both of which are important for stability and transport analyses, are also quantified. Examples of circular plasmas under various confinement modes, including the supershot and L mode, will be given.
Microwave polarimetry system in the CDX-U tokamak
Authors: Hwang Y. S. , Fredriksen Å. , Qin H. , Forest C. B. , Ono M.
Published: July 2002

An existing microwave interferometer system is modified to add the capability of polarimetry in the CDX-U tokamak. Though this interferometer system can scan vertically and radially, only the vertical view channel is modified to accomodate Faraday rotation measurements, with its radial scanning capability preserved. For our relatively long microwave wavelength, the signal amplitude variation due to refraction is more important than effects due to vibration. An amplitude independent design of Faraday rotation diagnostics has been developed. By using a linearly polarized beam as input and putting a rotating polarizer in the beam after the plasma, birefringency effects are minimized. A digital phase detection technique has been developed for better resolution of the Faraday rotation angle.
Single-chord polarimetry results on RFX (abstract)
Authors: Zilli E. , O’Leary P.
Published: July 2002

A single-chord FIR polarimeter (λ=118.8 μm) has been mounted on RFX and is now under test. The purpose of the diagnostic is to ascertain the feasibility of measuring a Faraday rotation effect in the RFX plasma and to discover what requirements are necessary for a future six-chord diagnostic. The diagnostic should measure small Faraday rotation angles (of the order of a few degrees) and the required resolution is of ±0.2°. The tests carried out reveal various sources of disturbance: electrical disturbance in the signals, vibration effects on the optical components, detector noise, and perturbations on the laser system (a CO2 laser pumping a FIR cavity). Several modifications to the system have been successful either in removing or reducing the effects of these disturbances.
Digital interface for quadrature demodulation of interferometer signals (abstract)a)
Authors: Waller J. , Shi X. H. , Altoveros N. C. , Howard J. , Blackwell B. D. , Warr G. B.
Published: July 2002

We describe a digital interface for processing signals produced by a scanning multichannel far-infrared interferometer/polarimeter for plasma density measurements. The interface samples the interferometer signals in quadrature before digital filtering, demodulation and downloading to a transputer array for real-time tomographic inversion and display.
First testing of the fast kappa diffractometers at National Synchrotron Light Source and European Synchrotron Radiation Facility
Authors: Robinson I. K. , Graafsma H. , Kvick A. , Linderholm J.
Published: July 2002

We present the design and first results of the performance of a new four-circle x-ray diffractometer featuring the less-common ‘‘kappa’’ geometry originally used on the CAD-4 instrument. This geometry permits access to all reciprocal-space settings while the mechanical supports remain entirely on one side of the beam; this is very useful for split ports on bending-magnet beamlines. Our design is able to carry heavy loads, such as a Displex-type cryostat, and operates at relatively high speeds because it uses direct drive servomotors. Considerable attention has been given to the distribution of loads which is optimized for horizontal-axis operation. A sphere of confusion of 50 μm was achieved fairly easily for the mutual alignment of the axes, and this can probably be improved. Our initial tests show that accurate alignment of crystals can be achieved, and reliable measurements have been made on a number of experimental systems. Rocking curves of silicon have been measured, but these are at the limit of the setting accuracy. Arbitrary settings are achieved in about 1 s, but up to an additional 1 s settling time is needed for high accuracy work.
Beam emission imaging system for 2D plasma turbulence measurements
Authors: Thorson T. A. , Durst R. D. , Fonck R. J.
Published: July 2002

A two-dimensional analog to the beam emission spectroscopy (BES) diagnostic has been designed to acquire vorticity and plasma flow-field information by resolving the spatial and temporal intermittency of plasma turbulent structures. The beam emission imaging diagnostic measures collisionally induced neutral beam fluorescence to infer local plasma density variations. It consists of a high-throughput, interline-transfer CCD camera viewing, with narrow spectral bandwidth, a 10 cm high diagnostic neutral beam as it traverses the plasma. The camera is coupled to a gated image intensifier that provides for two images with exposure times up to a few ms to be separated by as little as 10 μs. Sensitivity to density fluctuations of ñ/n≳1.0% is expected using the Phaedrus-T beam operating at 20–25 keV in He0 or D0.
Design of the divertor Thomson scattering system on DIII-D
Authors: Carlstrom T. N. , Foote J. H. , Nilson D. G. , Rice B. W.
Published: July 2002

Local measurements of ne and Te in the divertor region are necessary for a more complete understanding of divertor physics. We have designed an extension to the existing multipulse Thomson scattering system [Carlstrom et al., Rev. Sci. Instrum. 63, 4901 (1992)] to measure ne in the range 5×1018–5×1020 m−3 and Te in the range 5–500 eV with 1 cm resolution from 1 to 21 cm above the floor of the DIII-D vessel (eight spatial channels) in the region of the X point for lower single-null diverted plasmas. One of the existing, 20 Hz, Nd:YAG lasers will be redirected to a separate vertical port and viewed radially with a specially designed f/6.8 lens. Fiber optics carry the light to polychromators whose interference filters have been optimized for low Te measurements. Other aspects of the system, including the beam path to the vessel, polychromator design, real-time data acquisition, laser control, calibration facility, and DIII-D timing and data acquisition interface, will be shared with the existing multipulse Thomson system. An in situ laser alignment monitor will provide alignment information for each laser pulse.
Proposed improvements for torsional wave measurements of density and viscosity
Authors: Friesel M. A.
Published: July 2002

A first-order theory has previously been developed to allow the measurements of density and viscosity of fluids using the time-of-flight of torsional waves in immersed waveguides. In this article the theory has been modified to eliminate the need to calculate fluid-independent constants, via the use of two reference fluids. The effects of temperature differences among the reference and test fluids for moderately low temperatures are also examined. The result is a simple matrix equation which can be solved for the unknown fluid density. Fluid viscosity can be determined using an auxiliary equation.
Magnetic field mapping with an array of nuclear magnetic resonance probes
Authors: Hammer Bruce E.
Published: July 2002

Magnetic field maps can rapidly and accurately be acquired on the surface of a cylinder or sphere with an array of nuclear magnetic resonance (NMR) coils multiplexed to a single radiofrequency receiver. Using an array of NMR probes significantly decreases the time necessary to map B0 and improves field map accuracy because the probes do not move. The spatial variation of the Larmor frequency is used to determine the spherical harmonic components present in the field. A limitation of this approach is that NMR resonant circuits are inherently narrow band which limits the apparatus to a specific field strength and only points in space defined by the array layout. This apparatus can characterize the magnetic fields of high homogeneity dipole magnets, quadrupole magnets, gradient coils, and shims used in NMR imaging systems.
High-speed atomic force microscopy using an integrated actuator and optical lever detection
Authors: Manalis S. R. , Minne S. C. , Atalar A. , Quate C. F.
Published: July 2002

A new procedure for high-speed imaging with the atomic force microscope that combines an integrated ZnO piezoelectric actuator with an optical lever sensor has yielded an imaging bandwidth of 33 kHz. This bandwidth is primarily limited by a mechanical resonance of 77 kHz when the cantilever is placed in contact with a surface. Images scanned with a tip velocity of 1 cm/s have been obtained in the constant force mode by using the optical lever to measure the cantilever stress. This is accomplished by subtracting an unwanted deflection produced by the actuator from the net deflection measured by the photodiode using a linear correction circuit. We have verified that the tip/sample force is constant by monitoring the cantilever stress with an implanted piezoresistor.
Increased uniformity and thermal stability of CoSi2 thin films by Ti capping
Authors: Tung R. T. , Schrey F.
Published: July 2002

A thin (1–3 nm) Ti layer is shown to improve the uniformity and the thermal stability of CoSi2 layers grown on Si substrates. The beneficial effect of the Ti(TiN) cap is demonstrated for a variety of CoSi2 layers, including Ti-interlayer mediated epitaxial (TIME) CoSi2/Si(100), polycrystalline CoSi2/Si(100), and CoSi2/polycrystalline Si. The increased uniformity and stability of the silicide layers are speculated to result from reduced surface and interface diffusion during nitrogen and/or vacuum anneals. In the case of TIME CoSi2/Si(100), both the use of a Ti cap and the removal of a metastable Ti4Co4Si7 overlayer prior to high-temperature anneals are found important for the fabrication of uniform, single-crystal layers.
In situ grazing incidence x-ray diffraction system for clusters deposited on a low-temperature substrate
Authors: Koga Kenji , Takeo Harutoshi
Published: July 2002

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.
Autocalibrating quasistatic M-H hysteresis loop tracer with negligible drift
Authors: Franco V. , Ramos-Martos J. , Conde A.
Published: July 2002

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.
New photothermal deflection method for thermal diffusivity measurement of semiconductor wafers
Authors: Bertolotti M. , Dorogan V. , Liakhou G. , Li Voti R. , Paoloni S. , Sibilia C.
Published: July 2002

The photothermal deflection technique is applied in transverse configuration to measure the thermal diffusivity of semiconductor wafers. The large size of these samples inhibits the possibility to make the probe beam skim the sample at a small height which is required for a direct thermal diffusivity measurement. To overcome this problem, three new experimental schemes are proposed, each one based on a different geometry of the heat diffusion (one-, two-, or three-dimensional scheme). In particular for the 3D experimental scheme, a new mirage setup is described which uses two crystalline prisms 6 mm apart from each other to let the probe beam skim 50±3 μm high over the sample surface, with a spot size of 22 μm. The main advantages of this setup, here discussed, are the obtained low probe beam height which is, moreover, independent of the sample dimensions, and the cheap technology to produce the necessary high-quality prisms. The performances of the new schemes have been tested by comparing, for well-known semiconductor wafers (InSb, InAs, InP, GaAs, GaP, Ge, and Si), the experimentally measured thermal diffusivity with the values reported in the literature.
Signal-to-noise enhancement in optical spectroscopy of single indium ions using amplitude modulation and synchronous detection
Authors: Burt E. , Nagourney W.
Published: July 2002

A technique for reducing background and improving the signal-to-noise ratio in optical spectroscopy of weak atomic transitions is described. In this technique an incident laser is square-wave amplitude modulated and the resonance fluorescence from the atom is then detected out of phase with the excitation when the laser is off. Due to the finite lifetime of the atom’s excited state, appreciable signal is observed when the laser is off and instrumental scattering background is virtually eliminated. Applying this technique to an experiment on single laser-cooled In+ ions, we have observed a factor of 500 reduction in background and a factor of 5 increase in the signal-to-noise ratio.
Gridded retarding pressure sensor for ion and neutral particle analysis in flowing plasmas
Authors: King Lyon B. , Gallimore Alec D.
Published: July 2002

Although classical electrostatic plasma probes can provide detailed information regarding electrons and ions, these devices rely on charge-carrying particles both for energy filtering and for detection. Neutral particles are transparent to such diagnostics. In light of this a new probe design was developed to provide a measurement of the neutral particle flux component of a flowing plasma. The simple design adopted for this probe utilizes a set of electrostatic retarding grids to remove the charged particles from the flow. The neutral particles are sensed within the tube of an off-the-shelf hot cathode ionization gauge. Additionally, by varying the potential on the retarding grids, this same probe configuration can be used to measure the ion energy distribution. Preliminary data from this probe were taken in the exhaust plume of a Hall-current accelerator designed for space propulsion. This probe was found to be a very simple, accurate diagnostic tool for such use. By using this probe in combination with interrelated diagnostics the spatial distribution of energetic charge exchange neutrals was quantified in the plume of an SPT-100 thruster.
Flexible microwave system to measure the electron number density and quantify the communications impact of electric thruster plasma plumes
Authors: Gilchrist B. E. , Ohler S. G. , Gallimore A. D.
Published: July 2002

An advanced microwave interferometric system operating in the Ku (12–18 GHz) band has been implemented for use in very large vacuum chambers to determine the effects of electromagnetic wave propagation through a plasma plume created by a space electric propulsion thruster. This diagnostic tool is used to nonintrusively obtain the local electron number density as well as provide information necessary for understanding impact to communications and other spacecraft electromagnetic systems. The use of a nonintrusive electromagnetic measurement provides highly accurate line integrated density and avoids problems caused by intrusive measurement techniques. If the plasma is symmetrical, local plasma density can also be determined accurately using well known inversion techniques. A network analyzer acts as a transmitter and receiver while a two axis positioning system maps the amplitude and phase variation of a transmitted signal over one plane of the plasma plume. The utilization of a 6 m×9 m vacuum chamber effectively minimizes plasma boundary effects, but the longer cable path lengths have required a frequency conversion circuit to reduce power loss and phase uncertainty at high frequencies. Two studies are presented: the first is a measurement of the local electron density in the plume of a 1 kW arcjet and the second is a measurement of attenuation in the plume of a stationary plasma thruster. Both the arcjet and SPT emit a steady state conical unmagnetized plasma that is radially symmetric. The arcjet peak density is 1015–1016 m−3 along centerline and the SPT peak density is 1016–1017 m−3 along centerline.
Realization and characterization of a transmission line compression circuit for low impedance pulse power generation
Authors: Nassisi Vincenzo
Published: July 2002

A high efficiency pulse compression circuit utilizing transmission lines and transistor switches has been realized. It yielded a time compression factor of 2. An input pulse of 2.8 A and 140 ns long was produced by means of a pulse-forming line and a fast transistor switch. This pulse was compressed using a second fast transistor switch, a storage line, and a load impedance half that of the transmission and storage lines. The output current became 5.2 A. The energy transfer efficiency was limited by the transistor switch capacitance which transmitted the edge of the pulse before the switch closed.
A cell for in-plane, isotropic external stressing of thin films: Inverse magnetoelastic effects
Authors: Callegaro Luca , Puppin Ezio , Petrali Davide
Published: July 2002

We describe a cell to study the effect of isotropic in-plane stresses on the properties of thin films: the working principle is the uniform inflation of the substrate of the film with a pressurized fluid. In order to investigate inverse magnetoelastic effects on thin ferromagnetic films, a setup composed of the cell and a magneto-optical ellipsometer is also described. Preliminary results onto electroplated Ni film are shown.
Analysis of the double exponential behavior in alexandrite for optical temperature sensing applications
Authors: Sun T. , Zhang Z. Y. , Grattan K. T. V. , Palmer A. W. , Collins S. F.
Published: July 2002

An analysis of the fluorescence decay behavior of alexandrite emission, at higher dopant concentrations, has been undertaken for optical sensor application purposes. A double exponential decay behavior of the fluorescence emission has been observed, which differs from the single exponential behavior of alexandrite at lower concentrations of the active Cr 3+ ion. The origin of the phenomenon has been investigated both experimentally and theoretically and found to be produced by the joint contribution from the Cr3+ dopant in both the mirror, as well as in the inversion sites of that ion. The two lifetimes resulting, each having a different temperature dependence, both can be represented through the use of the configurational coordinate model which considers the effect of thermal quenching. The intensity ratio of these two aspects is seen to change regularly with the temperature within the important region for sensing of 273–773 K, and thus provides an alternative means to produce a calibrated fluorescence-based sensor.
A scanning force microscope with atomic resolution in ultrahigh vacuum and at low temperatures
Authors: Allers W. , Schwarz A. , Schwarz U. D. , Wiesendanger R.
Published: July 2002

We present a new design of a scanning force microscope (SFM) for operation at low temperatures in an ultrahigh vacuum (UHV) system. The SFM features an all-fiber interferometer detection mechanism and can be used for contact as well as for noncontact measurements. Cooling is performed in a UHV compatible liquid helium bath cryostat. The design allows in situ cantilever and sample exchange at room temperature; the subsequent transport of the microscope into the cryostat is done by a specially designed transfer mechanism. Atomic resolution images acquired at various temperatures down to 10 K in contact as well as in noncontact mode are shown to demonstrate the performance of the microscope.
Superconducting hexapole/solenoid for SERSE
Authors: Krischel D. , Schillo M. , Hobl A. , Grüneberg H. , Hergesell H.-J.
Published: July 2002

We review the design, fabrication, and test of the coldmass of the superconducting hexapole/solenoid for the source SERSE (superconducting electron cyclotron resonance source) built in a joint venture between INFN, Catania, and CEA/DRFMC, Grenoble. Following the magnetic field specifications we did the optimization of coil shape and positioning to keep the induction in the coil heads at the necessary minimum. The forces acting on the coil heads due to the combined hexapole/solenoid field nevertheless are of highly complex structure. Therefore special attention was given to the structural analysis including 3D coil head simulations. According to ACCEL’s experience with s.c. wigglers and wavelength shifters the 700 mm long racetrack coils were imbedded into a stainless steel structure being completed by a set of structural wedges and shrink rings. After assembling of the quench protection diodes the magnet has been cold tested in a temporary cryostat and after a reasonable number of quenches it achieved all levels of performance for the axial profiles and the hexapolar field specified by INFN. Subsequently the training was continued to the exceptional maximum field of 1.54 T at the position of the plasma chamber wall (radius 65 mm), which is 10% above specification. The completed coldmass has been integrated into its final cryostat and is being tested at CEA.
Beam formation at the Munich atomic beam source
Authors: Hertenberger R. , Eisermann Y. , Hofmann A. , Metz A. , Schiemenz P. , Trieb S. , Graw G.
Published: July 2002

A Stern–Gerlach atomic-beam ion source (ABS) with an electron cyclotron resonance (ECR) ionizer and a Cs gas target as charge exchange units will replace the Munich Lamb–Shift polarized hydrogen source. The goal is to achieve intense negative beams of polarized H− and D− of high brightness for injection into the 14 MV MP tandem accelerator and beam intensity of about 2 μA on the target. At the entrance of the ECR ionizer the observed intensity of the neutral beam of polarized atoms is 6.4±0.4×1016 H/s, equivalent to 10 particle/mA before ionization. Comparing beam transport calculations with beam intensity measurements under various conditions allows a consistent description of the beam formation in the ABS with respect to the degree of dissociation (≃80%), peaking (≃1.6), beam absorption (≃40%), and pumping speeds to be made.
Extraction of molecular negative-ion beams of CN from radio frequency plasma-sputter-type heavy negative ion source for negative-ion beam deposition
Authors: Tsuji Hiroshi , Ishikawa Junzo , Tomita Tetsuo , Yoshihara Takaaki , Gotoh Yasuhito
Published: July 2002

A high current CN negative-ion beam was obtained from a radio frequency plasma-sputter-type heavy negative ion source in a target-gas mode operation and CN negative-ion beam deposition was investigated. CN negative ions of 0.88 mA were safely obtained by using a carbon sputtering target and nitrogen gas instead of cyanogen for ionization. Even in this target-gas mode operation of the source with N2 gas, the work function of the sputtering target surface was effectively decreased by introducing cesium vapor so that the production of CN negative ions was remarkably enhanced. In a CN negative-ion beam deposition on silicon substrate, the nitrogen concentration in deposited layers depended on ion energy and the maximum ratio (N/C) of 0.3 was obtained at an energy of 70 eV. From a Raman spectra with these results, it was found that CN-deposited films were a diamondlike carbon film including nitrogen atoms.
Observation of different Ta and Pt ion groups produced by laser radiation with the intensities of I λ2∼1015 W cm−2 μm2
Authors: Mróz W. , Láska L. , Krása J. , Králiková B. , Mašek K. , Pfeifer M. , Rohlena K. , Skála J. , Parys P. , Wołowski J. , Woryna E. , Fry D. , Stockli M. P.
Published: July 2002

Ions produced in a process of interaction of the intense laser radiation of the iodine laser system PERUN (λ=1.315 μm, EL⩽50 J, τ∼350 ps, Iλ2∼1015 W cm−2 μm2) with the solid state tantalum and platinum targets have the ionization states from z=1 up to z∼50 and energies at least a few MeV. The Thomson parabola (TP) ion spectrograph with a registration system based on the micro channel plate (MCP) used in the experiment, gives a general view of ionization states and energies of all types of ions created in one laser shot. The data registered by the PC, gives on-line information on the obtained experimental results. As shown, the calibration measurements of MCPs, made with Ta ions (MCPs different from these used with the TP), analog particle gain of the MCPs rises with the increase in the ion charge states and energy. This attribute causes an increase in sensitivity of MCPs on the highly charged, high energy ions. The registered ions are composed of a few groups of ions with different charge states and different energies. In the experiment with the TP, the ring, ion collector (IC), coaxial with its axis has been used. From a comparison of the velocities of different ion groups registered by the IC and by the TP, the quantity of ions in different ion groups was estimated.
Scanning force microscope and vacuum chamber for the study of ice films: Design and first results
Authors: Bluhm H. , Pan S. H. , Xu L. , Inoue T. , Ogletree D. F. , Salmeron M.
Published: July 2002

We present the design of a scanning force microscope and vacuum chamber for the growth and imaging of ice films in thermodynamic equilibrium and under controlled super or undersaturation. The apparatus allows measurements in the temperature range from −60 to +80 °C in a controlled water vapor atmosphere. First results on the morphology and the frictional properties of thin ice films on mica cleavage faces are presented. The films are found to grow in a two-dimensional manner, often exhibiting dendritic growth shapes. The lateral force measured on ice is higher than that observed on the surrounding substrate.
An external electronic feedback system applied to a cryogenic μ-calorimeter
Authors: Galeazzi M.
Published: July 2002

In order to improve the maximum counting rate of cryogenic μ-calorimeters used as particle detectors, the application of an external electronic feedback (EEF) system is under development in Genoa, Italy. A description of the experimental setup of such a system and a model which describes the properties of the EEF applied to a current biased μ-calorimeter is reported. The model shows the maximum performance obtainable with such a system, which in principle allows one to improve the detector speed by some orders of magnitude. The model includes also a theoretical noise analysis and the calculation of the intrinsic energy resolution obtained using this kind of system, showing that the EEF does not worsen the energy resolution. The theoretical calculations have been compared with the experimental results obtained in Genoa. The comparison shows a good agreement between theoretical predictions and experimental results. In particular it has been possible to reduce the pulse length, considered as equal to five time constant, from more than 110 ms to less than 4 ms, gaining about a factor of 30 in the detector speed. The corresponding energy resolution with the feedback system is 1.75 times worse than without the feedback system.
Application of high performance inverter circuit to plasma generation and heating in fusion devices
Authors: Watanabe Shinichi , Uesugi Yoshihiko , Ohsawa Shigeyuki , Takamura Shuichi
Published: July 2002

We have constructed a rf power source using static induction transistor (SIT) inverters to generate high heat flux plasmas in the diverter plasma simulator, NAGDIS-II. Since the SIT can enlarge the operating frequency range of the high power inverter above 1 MHz with output power of several tens of kW, SIT inverters can be used to generate rf plasmas and to heat plasmas by exciting low frequency plasma waves, such as Alfven waves and ion cyclotron waves in plasma devices. The rf conversion efficiency of a SIT inverter with matched load is >85% for frequencies up to 1.2 MHz. The third harmonic antenna current is found to be less than −30 dB. Using four sets of inverter power supplies, we can generate more than 56 kW in continuous rf power or 80 kW in 1 s pulses to produce high heat flux plasmas in the diverter plasma simulator.
Nonintrusive rigid body tracking technique for dry particulate flows. Part II. Practical aspects and implementation
Authors: Dave Rajesh N. , Volcy J. , Agarwal J. , Gupta V.
Published: July 2002

A system, based on the principle of magnetic induction coupling, to track a particle nonintrusively in three dimensions is presented. It consists of small transmitters mounted inside the particle being tracked, and a set of receiving antennae surrounding the experimental apparatus. In Part I of the sequence of two papers, the focus is on the theoretical aspects, in particular, on developing a computational technique to solve the inverse problem of finding the three-dimensional position as well as orientation of the particle from the voltages induced in the antennae. In Part II the focus is on the actual system development, including all hardware and data acquisition aspects. The results presented here are comprehensive, as they include details of hardware/electronics, comparison of induced voltage model and actual measurements, and a set of actual tracking results. Through test experiments that include a variety of real-time trajectories, this system is tested and its success is demonstrated. Results of real trajectories of a single ball rising in a mass of other spheres in a vibrated bed are also shown. Although this system is intended for use in experimental studies of dry granular flows, it has wide applicability due to its nonintrusive nature, and is particularly useful when optical tracking techniques are not feasible.
Development of a temperature-programed electron-stimulated desorption ion angular distribution/time-of-flight system for real-time observation of surface processes and its application to adsorbed layers on Ru(001)
Authors: Sasaki Takehiko , Iwasawa Yasuhiro
Published: July 2002

A temperature-programed (TP) electron-stimulated desorption ion angular distribution (ESDIAD)/time-of-flight (TOF) system was developed in order to observe surface processes in real time by ESDIAD images and to measure TOF spectra of desorbing ions for identification of the mass and the kinetic-energy distribution of ions. The instrumentation of this system is described. This system was applied to (∛×∛)R30°-CO/Ru(001) (0.33 ML) and CO-saturated Ru(001) surfaces. As for the (∛×∛)R30°-CO/Ru(001), the increase of the half width at half maximum of the ESDIAD images upon annealing was found corresponding to the thermal excitation of the bending mode and/or hindered translation. On the other hand, as for the CO-saturated surface, the static disorder of the molecular axis of CO was larger, and apparent thermal excitation was not observed. After partial desorption of CO from the CO-saturated surface where the surface changes into the ∛×∛ structure at 400–430 K, the yield of O+ increased due to the change in the adsorption site of CO. TOF spectra for ammonia adlayers (NH3 and ND3) were also measured by the developed system and the isotopic ratios for ESD yields depending on the adsorption states (chemisorbed first layer and physisorbed second layer) were obtained.
Fast movable remotely controlled Langmuir probe system
Authors: Pedrosa M. A. , López-Sánchez A. , Hidalgo C. , Montoro A. , Gabriel A. , Encabo J. , de la Gama J. , Martı́nez L. M. , Sánchez E. , Pérez R. , Sierra C.
Published: July 2002

A versatile remotely controlled fast reciprocating Langmuir probe has been developed for the TJ-II stellarator. The main components of the system are a removable head, containing the measurement tips, and a displacement system that enables the probe to be displaced in vacuum. The probe displacement system has two different components: a slow one (course length⩽0.8 m) to set the probe at the initial measurement position, and a fast one (run length=0.1 m) to obtain the desired measurements within an adjustable time interval during the plasma discharge. The radial movement of the probe is controlled remotely by means of a programmable logical control system, with a radial resolution of better than 1 mm. The fast displacement of the probe (up to 1.7 m/s) is achieved by using a pneumatic system. Its position as a function of time is monitored by means of the on-line response of a linear resistor attached to the fast displacement system.
Plasma networking in magnetically confined plasmas and diagnostics of nonlocal heat transport in tokamak filamentary plasmas
Authors: Kukushkin A. B. , Rantsev-Kartinov V. A.
Published: July 2002

The method of multilevel dynamical contrasting is applied to analyzing available data from tokamak plasmas. The results illustrate a possibility of extending the concept of the plasma percolating networks in dense Z pinches (and other inertially confined plasmas) to the case of magnetically confined plasmas. This extension suggests a necessity to append the conventional picture of the nonfilamentary plasma (which is nearly a fluid described by conventional magnetohydrodynamics) with a “network” component which is formed by the strongest long-living filaments of electric current and penetrate the “fluid” component. Signs of networking are found in visible light and soft x-ray images, and magnetic probing data. A diagnostic algorithm is formulated for identifying the role of plasma networking in observed phenomena of nonlocal (non-diffusive) heat transport in a tokamak.
A beam position sensor for low power infrared laser diodes
Authors: Capineri Lorenzo , Masotti Leonardo , Mazzoni Marina , Toci Guido , Mazzinghi Piero
Published: July 2002

This article presents the design criteria, the prototype development, and application results of a low-cost four quadrants infrared (IR) detector. The detector was specifically developed as a position sensor for the alignment of low power IR laser diode beams, especially for spectroscopic applications. The detector consists of a polyvinilidene difluoride pyroelectric radiation sensor of 4×4 mm2 total surface area and of a four-channel high gain transimpedance amplifier, followed by a narrow bandwidth resonant filter for noise rejection. The overall single pixel responsivity resulted 3590 V root mean square /W̄ at 5.8 μm, and modulation frequency of 85 Hz. The beam spot centroid of a square-wave modulated laser diode emitting 85 μW̄ was determined using an algorithm evaluating the difference signals between diagonal elements along vertical and horizontal scanning directions. An uncertainty in the centroid position of 6 μm, in both directions, was obtained, mainly limited by the digitizing resolution of the 12-bit acquisition system.
Improved apparatus and procedures for the measurement of solubility of rapidly equilibrating solid–liquid systems to 90 °C
Authors: Capewell S. G. , Hefter G. T. , May P. M.
Published: July 2002

An improved apparatus for measuring solubilities of solid–liquid systems at temperatures to 90 °C is described. The apparatus has a high capacity (up to 56 samples) and a long term temperature stability of ±3 mK. The design allows the saturated solution to be multiply sampled and microfiltered at the equilibration temperature, making it particularly suited to rapidly equilibrating systems. The reliability of the apparatus and sampling procedures were tested by measuring the solubilities of NaCl, Na2SO4, and Na2CO3 in water. The data obtained showed a routine precision of ±0.05% relative and agreed to within ±0.1% of recommended International Union of Pure and Applied Chemistry values.
A new sniffer probe for the determination of hydrogen isotope ratios in the W7-AS stellarator
Authors: Zebisch P. , Taglauer E. ,   and the W7-AS Team
Published: July 2002

An improved sniffer probe was constructed for measurements of the hydrogen isotope ratio and impurities in the plasma edge of the W7-AS stellarator. Details of the new design and the probe performance are presented. The new design allows changing the head without breaking the vacuum in the torus. It has a high mechanical stability, effective screening of the magnetic field and high sensitivity. The gas dynamic properties of the probe are analyzed using transmission line calculus, resulting in a rise time of 114 ms for hydrogen. During the 1997 spring measurement campaign, H/D isotope ratio measurements were carried through showing considerable outgassing of the walls during and after the discharge. He glow discharges reduce the isotope ratio drastically. Results from a typical experiment day are presented together with the analytic procedure for determining the isotope ratio in both the plasma edge and in the neutral gas region between the plasma and the vessel walls.