bluuebunny/crossref_metadata_2025 huggingface dataset:
Beam diagnostics with localized space-charge waves
Authors: Wang J. G. , Reiser M.
Published: July 2002

A new method for the diagnostics of charged particle beams by employing localized space-charge waves is presented. The propagation of space-charge waves in the form of localized perturbations can be measured easily and accurately in experiments. The results carry valuable information about many beam parameters such as the wave speed, the geometry factor g for the longitudinal space-charge field, the beam radius, the beam impedance under longitudinal perturbations, etc. The principle of this technique and an experimental example are given in this article.
Determination of material properties by using the reflection pulse method
Authors: Dolocan Voicu
Published: July 2002

New methods based on the reflection pulse technique are developed to study material properties. Using them, Curie temperatures in magnetic and ferroelectric materials, transition temperature and penetration depth in superconductors and characteristics of semiconductors, and semiconductor devices are determined.
Depolarized Rayleigh scattering of polymeric materials and their oligomers: Instrument design, calibration, and data analysis issues
Authors: Sen Sumit , Galiatsatos Vassilios
Published: July 2002

The importance of obtaining dependable values of molecular optical polarizability anisotropy for polymers and their oligomers lies in their subsequent use in the rotational isomeric state theory and in calculations involving the components of the optical polarizability tensor. This work describes a depolarized Rayleigh scattering photometer able to determine optical polarizability anisotropy of oligomers, melts, and polymer compounds in solution with a combination of exceptional accuracy and high sensitivity. Two separate calibration techniques are reported that ensure the accuracy and preciseness of the results obtained from the measurements. Finally, data analysis procedures are reported that show the sensitivity of the results to the internal field correction.
Thermal response of CMOS-micromachined thermistor sensors under constant power and constant current excitation
Authors: Shen Bing , Lai Zhongsheng , Robinson A. M. , Allegretto W.
Published: July 2002

The resistance of a micromachined polysilicon thermistor sensor has been measured under excitation by both a constant current and constant power step. The time-varying and steady-state response of the polysilicon resistor at ambient pressures of 1 atm and 10−4 Torr were observed under various step amplitudes. The increase of resistance above its room-temperature value changed exponentially with time; the time constant varied inversely with the square of the current step amplitude but was constant with power step amplitude. The steady-state change of resistance varied linearly with the applied power under both modes of excitation. The time-varying and steady-state responses were as predicted by a simple analytic model developed. The steady-state operation of these devices at the two pressures permitted us to directly determine the energy losses by heat conduction through the surrounding gas and conduction through the support arms. At 1 atm, up to 90% of the heat loss is by conduction through the gas. The operation of the device was also simulated numerically and results were obtained in reasonably close agreement with experiment. The simulation also allows us to predict the amount of heat flow through the various support arms; 70% of the heat conducted by the support arms flows through 8 of the 20 support arms.
An inexpensive high-voltage regulator for charged-particle optics
Authors: Gostein Michael , Sitz Greg O.
Published: July 2002

An inexpensive regulator circuit for high-voltage but low-current applications, such as biasing electrodes for the manipulation of charged-particle beams, is described. Using multiple regulator circuits running in parallel, numerous outputs can be produced from a single high-voltage supply, resulting in significant cost savings.
Noncontact infrared reflection spectroscopy using optical fibers
Authors: Bunimovich D. , Belotserkovsky E. , Katzir A.
Published: July 2002

Silver halide infrared transmitting optical fibers are used in a noncontact mode to deliver and collect infrared radiation from a thin liquid sample on a highly reflecting substrate. The detected signal is a sensitive measure of the absorption spectrum of the liquid under study. Optimal placement of the fibers with respect to the sample was calculated and experimentally confirmed. The system provides a quantitative infrared spectrum with minimal sample preparation.
A simple, quantitative method for measuring pulsed soft x rays
Authors: Takahama Yoshio , Du Jian , Yanagidaira Takeshi , Hirano Katsumi
Published: July 2002

A simple quantitative image processing system for pulsed soft x rays with time and spatial resolution is described. The system consists of easily obtained commercial components including a microchannel plate–phosphor screen combination, a charge coupled device camera, an image memory board, and a personal computer. To make a quantitative measurement possible, the image processing is used in conjunction with measurement of the ‘‘phosphor screen current.’’ Performance of the system is examined using a soft x-ray source generated with a plasma focus device. The order of intensity, ∼1012 photons/s mm2 mrad2 0.01% BW of Ar K lines is observed for about 20 ns from the pinched plasma in which 3% of Ar is added to the 6 Torr H2.
High-temperature scanning tunneling microscope with a novel sample heater and interchangeable scan heads
Authors: McCann Lowell I. , Smalley Richard M. , Dubson M. A.
Published: July 2002

A UHV-compatible, high-temperature scanning tunneling microscope (STM) with a sample stage incorporating a Si wafer as a resistive heater is described. The design allows for rapid interchange of scanning tubes so that the maximum scan size can be varied. The thermal stability of the microscope is excellent, allowing real-time studies of faceting and grain growth of metal surfaces at temperatures up to 400 °C with a long term drift of ∼0.05 Å/s.
High-precision harmonic magnetic-field measurement and analysis using a fixed angle Hall probe
Authors: Hwang C. S. , Lin F. Y. , Huang T. H. , Jan G. J. , Tseng P. K.
Published: July 2002

A special theoretical concept involving the harmonic magnetic-field measurement and analysis method using a fixed angle Hall probe was developed at the Synchrotron Radiation Research Center (SRRC) for measuring as well as analyzing the triple bending achromat magnets of the storage ring. The method can be used to simulate the harmonic magnetic-field calculation of the two-dimensional (2D) ‘‘magnet’’ program. This method has a quite simple mechanism. The Hall plate was fixed at a 0° angle with respect to the horizontal plane of magnet to measure only the vertical field. Additionally, the 2D nonlinear least-square fitting was used to fit the mapping data so as to find the normal and skew multipole field strength. If necessary, the angle of Hall probe could be rotated 90° precisely for measuring the horizontal field. Consequently, the skew dipole field could be obtained. A real-time Hall-probe automatic magnetic-field measurement system was also developed for fulfilling the concept of the harmonic field measurement. Some special mapping trajectories for different kinds of magnets were discussed to match this special theoretical concept with the analysis methodology. This was done so as to obtain the reliable and accurate harmonic field strength. The accuracy and precision of the harmonic field strength measurement and analysis of this method being better than ±0.01% was confirmed by experimental results.
Improved optical tomography device
Authors: Zintl M. , McWilliams R.
Published: July 2002

We report the development of an improved optical tomography diagnostic which measures the velocity-space distribution of a laboratory plasma in two dimensions. The new device is capable of imaging plasma distributions over a wider range of magnetic fields and plasma column diameters than the previous design, while minimizing the risk of misdiagnosis due to perturbations caused by inserting the device in the plasma. Computer-aided control of the diagnostic allows a greater number of single-dimensional scans to be collected in a shorter amount of time, resulting in increased resolution of the reconstructed image while freeing up more time for the user to perform the experiment. Recent data using the new device are presented to show improvement of resolution gained by doubling the number of total scans. Finally, we present a method to identify velocity-space nonuniformities without the need to reconstruct a complete image.
Gated x-ray imager gain correction using a tapered microchannel-plate stripline
Authors: Watt R. G. , Oertel J. , Archeluta T.
Published: July 2002

Gated imagers used to record x-ray emission in the 1–5 keV range in laser-plasma interaction experiments have suffered from resistive gain degradation between voltage drive pulse input and output ends of a microchannel-plate stripline. The reduction in gain as the pulse travels down the strip results in a lower signal-to-background ratio in the last image on a strip than in the first image. Compensation for this gain nonuniformity using a tapered stripline in place of the normally straight striplines is discussed.
Liquid scintillation detectors for gamma and neutron diagnostic at TEXTOR and results of runaway and sawtooth oscillations
Authors: Hoenen F. , Graffmann E. , Finken K. H. , Barrenscheen H.-J. , Klein H. , Jaspers R.
Published: July 2002

Time and energy resolved neutron and gamma measurements are performed at the TEXTOR tokamak with a fast liquid NE-213 scintillator. To distinguish between neutron and gamma (γ)-ray induced events, pulse shape discrimination is used. To suppress scattered radiation, the detector is installed in well-shielded collimators aligned radially or tangentially to the plasma current. Count rates up to 2–3×105 s−1 can be processed without considerable reduction of n/γ discrimination and without gain instability. To demonstrate the capability of this system, typical results are presented as obtained from plasmas in TEXTOR during sawtooth oscillations, runaway discharges, pellet injection, and neutral beam injection.
Ion temperature measuring probe in a strongly magnetized plasma
Authors: Amemiya H. , Uehara K.
Published: July 2002

A probe for the measurement of the ion temperature in a strongly magnetized plasma is described. The positive-ion current to a cylindrical probe, whose axis is set parallel to the magnetic field, is calculated in the collision-free regime as a function of the ion temperature and the magnetic-field strength. It is assumed that the electron Larmor radius is negligibly small compared to the radius of the cylinder. Only the ion Larmor radius is treated as finite. The ion temperature can be evaluated from the ratio of ion currents of the two cylindrical electrodes with different lengths, whose surfaces are parallel to the magnetic field. The effect of ion drift along the cylinder axis is also considered. Experiments have been made in the edge plasma of a JFT-2M tokamak to test the above probe for determining plasma parameters during ohmic and NBI heatings.
A simple method to perform measurements near the critical temperature in YBCO samples
Authors: Fontana F. , Persico V. , Valentino M.
Published: July 2002

A simple and reliable method to perform measurements of the electronic properties of YBCO samples in the very proximity of the critical temperature Tc is proposed and tested. A high degree of thermal stability of the sample at any desired temperature near Tc is achieved using a pressurized bath of liquid argon (LAr) in a close cryostat. Examples of measurements performed by such a technique are presented.
High-sensitive Pockels field sensor with a dielectric mirror
Authors: Murooka Y. , Nakano T.
Published: July 2002

The highly sensitive field sensor with a Pockels crystal which was devised by us has been modified by using a light reflection technique. By replacing a metallic mirror with a dielectric mirror which is sputtered on one end face of the Pockels crystal, the new field measuring system has an advantage of precisely measuring the field distribution in the long gap discharge. This is the case when the field sensing part consisting of the Pockels crystal is isolated from the main field measuring system and both are connected to each other with a long light guide cable. Based on our experiments, we found that the measurable minimum field strength in the long gap discharge is 2 V/cm with the accuracy of 16 dB and 0.2 V/cm with the critical accuracy of 0 dB. Furthermore, we point out that the size of the field sensing part can be reduced down to 1 mm in diameter by using a dielectric mirror and a light guide cable.
Resonance-tracking servo for an acousto-optic modulator
Authors: Krüger E. , Kersebom T.
Published: July 2002

A new scheme for locking an acoustic resonance of an acousto-optic modulator to the exciting rf field applied for laser mode locking is presented. The resonance of the mode-locking quartz prism is temperature-tuned to match the synthesizer frequency. Deviation from perfect matching is sensed by observing the relative phase of the rf wave reflected at the device, and the error signal is fed back by a servo loop adjusting the heat delivered by a heating transistor to maintain the temperature required for exact resonance. The performance of the resonance-tracking loop was checked on several different resonances of the modulator (used in an argon-ion laser), because switching to another resonance is a simple and attractive way for changing the laser pulse repetition rate (or mode spacing) without replacing the mode-locker unit. Excellent loop response was found in all cases. The new tracking principle provides a widely extended tracking range, improved tracking accuracy and laser stability, and simplifies the laser adjustment.
An adaptive scan generator for a scanning tunneling microscope
Authors: Heuell P. , Kulakov M. A. , Bullemer B.
Published: July 2002

A novel scan generator for a scanning tunneling microscope (STM) has been developed. The instrument compares tunneling current with three thresholds values, to generate an x-scanner signal with a dynamically changeable step size for adaptation to sharp topographical changes. It has two advantages compared to conventional STM scan generators (i) a better protection from a tip crash and (ii) minimization of the image acquisition time. The implementation is made with a digital signal processor (DSP) DSP32C from AT&T, mounted on a commercially available PC AT-compatible plug-in card. Test images of extremely rough surfaces confirm the usefulness of our novel scan generator. The concept could also be used for different scanning probe microscopes.
Ion beam noise reduction method for the MEVVA ion sourcea)
Authors: Oks E. , Spädtke P. , Emig H. , Wolf B. H.
Published: July 2002

The beam extracted from the MEVVA ion source tends to be of a relatively high noise level, particularly for the higher charge states, making beam transport difficult in accelerator application. This paper presents experimental results which show that the use of grids within the ion source in combination with a solenoidal magnetic field can decrease the noise of the extracted beam considerably. The noise reduction can be explained by an increase in plasma density due to the applied magnetic field and space charge limitation of the extracted ion beam current.
Temperature distribution, deformations, and x-ray diffraction in the inclined high heat load monochromator: Analytical solutions
Authors: Kushnir Vladimir
Published: July 2002

Analytical solutions for the temperature distribution and displacement field gradients in the high heat load monochromator are presented. The footprint of the incident x-ray beam on the crystal surface is approximated by an infinitely long narrow strip, which is applicable in the case of the inclined diffraction geometry. The two-dimensional problem in the cross section of the crystal normal to the footprint is considered. The solutions for the temperature distribution and displacement field gradients are found in terms of Fourier integrals. These expressions are also valid for x-ray mirrors. The deviation of the incident beam from exact Bragg position produced by this deformation is calculated. All numerical examples are calculated for the special undulator which is to be installed in the sector III of the Advanced Photon Source.
Analysis of the circular polarization rate delivered by an asymmetric wiggler and a two beryl crystal monochromator—Calculation and experiment
Authors: Lefebvre D. , Sainctavit Ph. , Malgrange C.
Published: July 2002

Synchrotrons are powerful sources of an x-ray beam whose polarization state is well defined. The recent apparition of insertion devices able to produce high flux of circularly polarized light has impulsed new fields of solid-state physics in spectroscopy or diffraction techniques. In this paper, the calculation of circular polarization rates taking into account the characteristics of the synchrotron source and the depolarization effect introduced by the beam monochromatization on crystals is presented here. From measurements of the circular polarization rates by x-ray magnetic circular dichroism at nickel L2,3 edges, the experimental results are in excellent agreement with the calculations.
1 kA low-energy electron-beam source
Authors: Hamagaki Manabu , Hara Tamio , Sadamoto Yoshiro , Ohgo Tadashi
Published: July 2002

A high-current electron beam up to 1 kA has been obtained at an acceleration voltage of 200 V for 1 ms in quasi-steady operation. Maximum power (250 kW) of the electron beam was achieved. The beam current can be controlled independently of the acceleration voltage by changing the discharge current of the plasma cathode. This electron-beam source is useful to pump a high current ion source for neutral beam injection in fusion research.
A computer simulation study on the detection efficiencies of parallel-plate electron multipliers
Authors: Suzuki S. , Konno T.
Published: July 2002

The detection efficiencies of parallel-plate electron multipliers with a parallel electric field (PPEM-parallel) and with a tilted electric field (PPEM-tilt) have been calculated by a Monte Carlo simulation method. The detection efficiencies vary with the geometrical conditions of the dynodes such as the dynode spacing, the dynode displacement, and the dynode length. Under the optimum geometrical conditions that give the maximum mean gains, the PPEM-parallels have a detection efficiency of 75% and the PPEM-tilts have a detection efficiency of 70% for an incident electron energy of 300 eV. These values do not vary with the applied voltage. Detection efficiency versus incident electron energy curves has been obtained for the optimum geometrical conditions. The forms of these curves are almost the same for the PPEM-parallel and the PPEM-tilt and do not change with the applied voltage.
Performance of a liquid-nitrogen-cooled, thin silicon crystal monochromator on a high-power, focused wiggler synchrotron beam
Authors: Rogers C. S. , Mills D. M. , Lee W.-K. , Knapp G. S. , Holmberg J. , Freund A. , Wulff M. , Rossat M. , Hanfland M. , Yamaoka H.
Published: July 2002

An experiment was performed on beamline BL 3 at the European Synchrotron Radiation Facility to test the diffraction performance of a novel internally liquid-nitrogen-cooled, thin silicon crystal monochromator exposed to high heat loads. The beam parameters were chosen to closely match the conditions expected, in terms of absorbed power and beam profile, at the Advanced Photon Source (APS) for the closed gap undulator at 7 GeV and 100 mA. The cooled crystal was oriented at 11.4° in the symmetric Bragg geometry to diffract 30 keV x-rays from the Si(333) planes. The source was a 44-pole wiggler with the insertion device gap set at 25.0 mm corresponding to a deflection parameter, K, of 4.2. A tunable toroidal mirror was used to focus the wiggler beam onto the crystal. Double-crystal rocking curves were measured at several power values using different attenuators. The maximum total power absorbed by the 0.6-mm-thick crystal was 154 W at a storage ring current of 136 mA. The peak power density at normal incidence was about 420 W/mm2 corresponding to an absorbed peak power density on the crystal face of 83 W/mm2. No thermal-induced broadening of the rocking curve was observed above the average measured mounting/fabrication strain of 2 arcsec. Rocking curves were also measured as a function of coolant flow rate and pressure. No systematic broadening occurred due to flow-induced vibrations up to 6 ℓ/min. It has been demonstrated that thin silicon crystals directly cooled with liquid nitrogen can handle high power density synchrotron beams comparable to what is expected for the APS undulators with no appreciable thermal deformation.
Variable-angle ultraviolet total-internal-reflection fluorescence spectroscopy using a white excitation light source
Authors: Toriumi M. , Saito S. , Kawaguchi K. , Aiki K.
Published: July 2002

An apparatus for variable-angle ultraviolet total internal reflection fluorescence (TIRF) spectroscopy is described. TIRF spectroscopy is an analytical technique based on the excitation of fluorescence from a sample by means of an exponentially decaying surface energy wave. The limited penetration depth of the excitation volume results in excitation of fluorescence only near the sample/substrate interface. The angular spectrum makes TIRF spectroscopy suitable for obtaining quantitative information on the depth profile of a sample. In the instrument described here, precise positioning of incident optics with correction of the chromatic aberration due to the xenon light source enables the measurement of the excitation spectrum. The system provides the fluorescence and excitation spectra for study of the physical and chemical properties of thin-film structures. The incident- and observation-angle dependences of those spectra give important information on the depth profiles of the fluorophores in the samples. The performance of the instrument is demonstrated with thin polymer films containing a fluorescent probe of pyrene. Pyrene monomer is found to form the nonuniform depth profile different from that of pyrene excimer.
A novel setup for spectroscopic ellipsometry using an acousto-optic tuneable filter
Authors: Fukarek W. , von Keudell A.
Published: July 2002

A rotating-analyzer ellipsometer for fast measurements at multiple wavelengths as well as for spectroscopic measurements has been developed. The most important novelty of the setup is the use of an acousto-optic tuneable filter (AOTF) as dispersing element. This offers advantages with respect to the speed of measurement, the adjustment of the intensity of the light, the use of lock-in techniques, and the stability and size of the setup. Advantages and limitations of the use of AOTF’s in ellipsometry as well as possible changes in the ellipsometric setup are discussed. The ellipsometer has been mounted on an electron cyclotron resonance plasma deposition chamber. As an example, the deposition of amorphous hydrogenated carbon layers has been studied in situ and are compared to ex situ measurements by variable angle of incidence spectroscopic ellipsometry of the same samples.
Novel method for measuring intense microwave radiation effects on ionic transport in ceramic materials
Authors: Freeman S. A. , Booske J. H. , Cooper R. F.
Published: July 2002

Many experimenters over the past few years have observed rate enhancements when using microwave processing compared to conventional processing. The results have remained somewhat controversial because the driving forces are not constant throughout the experiments and because of the possibility of inaccurate temperature measurement. This paper describes a different experimental approach that avoids the pitfalls of the previous experiments. Specifically, the alternative approach involves fixed driving forces and short duration experiments. Reliable and accurate knowledge of the sample temperature is ensured by restricting the amount of microwave heating to negligible levels and using conventional ohmic heating to control temperature. This approach has allowed us to confirm the presence of a ‘‘microwave effect’’ on kinetic processes in ionic ceramic materials. With this configuration, many further experiments are possible with different materials and conditions.
Comprehensive studies of electrohydrodynamic spraying of liquids
Authors: Krasnov N. V. , Shevchenko S. I.
Published: July 2002

A technique for the comprehensive study of electrohydrodynamic spraying of liquids is offered that makes it possible to control several spraying parameters simultaneously by various physical methods: optical, electrical (current–voltage characteristic), mass spectrometric, and photographic. An unambiguons correlation among the form of a current–voltage characteristic, spraying modes, and the shape of liquid surface has been obtained.
Advances in the design of a thermomechanical analyzer for fibers. I. Instrumental features
Authors: Noui L. , Hearle J. W. S. , Michielsen S.
Published: July 2002

A detailed description of new developments of the flexible thermomechanical analyzer for fibers (FTMA) is presented. The advances consist of a data acquisition system; an improved drive system, with potential for closed loop operation; a single tension transducer for slow and fast changes; reduction of mechanical vibration; use of fast thermocouples. A thorough investigation of the instrument included characterization of the temperature and tension sensing systems, and determination of their detection limits. Comparisons between FTMA performances before and after the introduction of changes clearly illustrate the improvements achieved. The combination of turbulence and inadequate mixing of hot and cold air causes temperature fluctuations, which need to be reduced. Other developments are planned.
Device for electron bunch length measurement in the picosecond region
Authors: Aleksandrov A. V. , Calabrese R. , Ciullo G. , Dikansky N. S. , Guidi V. , Lamanna G. , Lenisa P. , Logachov P. V. , Novokhatsky A. V. , Tecchio L. , Yang B.
Published: July 2002

We designed, created, and tested a device for measuring electron bunch length in the picosecond region. The basic idea behind the method is a circular scanning of the electron bunch in the rotating magnetic field of a TM110 rf cavity. As a result, the longitudinal position of the electrons is transformed into an angular position in a plane orthogonal to the axis. The resolution limit of the instrument is 4 ps (rms).
A double-focus lens interferometer for scanning force microscopy
Authors: Goto Kazuya , Sasaki Minoru , Okuma Shigeru , Hane Kazuhiro
Published: July 2002

We present a laser interferometer for displacement measurement requiring high precision. Consisting of a small number of optical parts, the instrument is simple, compact, and not affected by environmental conditions. Further, with a birefringent double-focus lens, the two interfering beams share a common path and the interference signal is immune to fluctuations of the optical path length. Peak-to-peak noise in a dc to 1 kHz bandwidth is less than 0.02 Å. We applied this interferometer to scanning force microscopy and tested the performance.
Use of parameters estimation method in the frequency domain for the simultaneous estimation of thermal diffusivity and conductivity
Authors: Guimarães G. , Philippi P. C. , Thery P.
Published: July 2002

The present paper presents a new experimental method developed for obtaining, simultaneously, the thermal conductivity and thermal diffusivity of nonmetallic materials. The method is based on signal treatment in the frequency domain. Two fast, high sensitivity heat flux transducers and two surface thermocouples measure the heat flux and temperatures, respectively. Time dependent temperature and heat flux signals at the boundaries define the equivalent complex impedance Z. Fourier transform is applied to these signals and the impedance Z is obtained in the frequency domain. The difference between the experimental values and the values of Z estimated using a theoretical model is then minimized. The result is the simultaneous estimation of the thermal diffusivity and thermal conductivity. The use of both the modulus and the phase of an equivalent complex impedance promotes a separation of parameters, which assures the obtained values of λ and α to be unique. Error analysis and a comparison with the steady-state method are also presented.
High sensitivity double relaxation oscillation superconducting quantum interference devices with large transfer from flux to voltage
Authors: Adelerhof Derk Jan , Kawai Jun , Uehara Gen , Kado Hisashi
Published: July 2002

Double relaxation oscillation superconducting quantum interference devices (SQUIDs) (DROSs) based on Nb/AlOx tunnel junctions have been fabricated and characterized. The estimated relaxation frequencies range from 400 MHz up to 14 GHz. Transfer coefficients from flux to voltage of 2 up to 7 mV/φ0 have been obtained. Both the intrinsic flux noise and the performance in a flux-locked loop with direct-voltage readout have been determined. Special attention is paid to the effect of damping resistors on the sensitivity of DROSs. The intrinsic sensitivity improves with increasing relaxation frequency, leveling off to a value of 13h at relaxation frequencies above 2–3 GHz for SQUID inductances of about 30 pH. This sensitivity is very close to the theoretical maximum sensitivity of 6h of a comparable standard type dc SQUID. In a flux-locked loop based on direct-voltage readout, a noise level of 0.55 μφ0/√Hz corresponding to an energy sensitivity of 34h has been obtained for a DROS with a SQUID inductance of 29 pH.
Compact sample manipulator providing azimuthal and flip rotations for operation between 16 and 1100 K
Authors: Michaud M. , Cloutier P. , Sanche L.
Published: July 2002

We report on the design and performance of a low-temperature sample manipulator for ultrahigh-vacuum surface studies. The arrangement consists essentially of modified commercial sample manipulator coupled to a closed-cycle helium refrigerator. The device allows a metal sample or a substrate, which is electrically isolated, to be cooled down to 16 K and heated up to 1100 K for cleaning and annealing purposes. Besides, the sample can be translated by ±0.5 cm in three perpendicular directions (X, Y, and Z axes), rotated by ±100° azimuthally along the main shaft (Z axis), and flipped over a range of 50° about an axis perpendicular to the main shaft. The sample holder, which includes the rotation supports, is sufficiently compact to be manipulated without hindrance as close as 1.4 cm from a given instrumentation. A simple mathematical model is developed to predict the cooling capacity of the present design or that of similarly constructed devices.
Novel wide-band Doppler LIDAR detection technique
Authors: Stoyanov D. V. , Bratanov B. M. , Stoykova E. V.
Published: July 2002

A novel wide-band Doppler LIDAR detection technique (up to GHz range), by using two sets of digitally selected reference frequencies, is developed. It combines the advantages of two well-known approaches—the analog quadrature detection (low sampling frequency and data rate, highly dynamic range) and the direct digitizing (fully digital controlling and processing without coherent oscillator minimum analog stages, very easy tuning) at the same accuracies as the Doppler estimates. This technique may be applied in airborne and satellite Doppler LIDARs as well as in low-cost ground-based systems using CO2 or solid-state laser sources.
Compact large-range cryogenic scanner
Authors: Siegel Jeffrey , Witt Jeff , Venturi Naia , Field Stuart
Published: July 2002

We describe the construction and operation of a large-range piezoelectric scanner, suitable for various scanning probe microscopies such as magnetic force, atomic force, and Hall probe microscopies. The instrument is compact and inherently thermally compensated. At room temperature, it has a range of over 2 mm; this range is reduced to 275 μm at 4.2 K.
Vertical photon beam position measurement at bending magnets using lateral diodes
Authors: Holldack K. , Peatman W. B. , Schroeter Th.
Published: July 2002

Commercial position sensitive diodes which were designed for measurements with visible light have been used to measure beam position in a white-light beamline, exposing them to the hard-x-ray part of the dipole spectrum. In preliminary studies it was found that the quantum efficiency of the lateral diodes is comparable to that of Si XUV diodes. At 1.5 keV a quantum efficiency of about 100 electrons per photon was measured in the central position. No long-term drifts of the efficiency have been observed. The position sensitivity of the diodes is almost independent of photon energy, but is at least a factor of 2 higher than in the visible range. Hence in a white-light beam, a photon energy window was defined by a water-cooled Al-absorber foil of 200 μm thickness. Behind the foil two lateral diodes were arranged at 3.5 (15 mm length) and 7 m (30 mm length) behind the source. The horizontal position of the diodes was staggered so that the first diode does not occlude the beam to the second one. With this system, the vertical source position in a bending magnet can be detected with 10 μm accuracy while the emission angle can be detected down to values of 2 μrad.
A variable temperature ultrahigh vacuum atomic force microscope
Authors: Dai Q. , Vollmer R. , Carpick R. W. , Ogletree D. F. , Salmeron M.
Published: July 2002

A new atomic force microscope (AFM) that operates in ultrahigh vacuum (UHV) is described. The sample is held fixed with spring clamps while the AMF cantilever and deflection sensor are scanned above it. Thus, the sample is easily coupled to a liquid nitrogen cooled thermal reservoir which allows AFM operation from ≊100 K to room temperature. AFM operation above room temperature is also possible. The microscope head is capable of coarse x-y positioning over millimeter distances so that AFM images can be taken virtually anywhere upon a macroscopic sample. The optical beam deflection scheme is used for detection, allowing simultaneous normal and lateral force measurements. The sample can be transferred from the AFM stage to a low energy electron diffraction/Auger electron spectrometer stage for surface analysis. Atomic lattice resolution AFM images taken in UHV are presented at 110, 296, and 430 K.
A one-dimensional numerical study of ultrashort-pulse reflectometry (abstract)a)
Authors: Cohen Bruce I. , Afeyan Bedros B. , Chou A. E. , Luhmann Neville C.
Published: July 2002

This article presents a first analysis elucidating theoretical aspects of ultrashort-pulse reflectometry. It is studied by means of the numerical integration of a one-dimensional full-wave equation for ordinary modes propagating in a plasma. The numerical calculations illustrate the potential of using the reflection of ultrashort-pulse microwaves as an effective probe even in the presence of significant density fluctuations. The difference in time delays of differing frequency components of the microwaves can be used to deduce the density profile. The modification of the reflected pulses in the presence of density fluctuations is examined and can be understood based on considerations of Bragg resonance. A simple and effective profile-reconstruction algorithm using the zero crossings of the reflected pulse and subsequent Abel inversion is demonstrated. The robustness of the profile reconstruction algorithm in the presence of a sufficiently small amplitude density perturbation is assessed.
Performance simulations of the medusa neutron detector array (abstract)
Authors: Kremens R. L. , Russotto M. A. , Tudman S.
Published: July 2002

A 960-channel neutron detector array is under construction to measure various neutron reaction products from direct-drive laser-driven inertially confined fusion experiments. Analytical and Monte-Carlo model simulations have been completed which demonstrate the usefulness of this diagnostic for broad classes of fusion experiments. The modeling accounts for neutron production rate and spectra from the target and detector and acquisition electronics response. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460 and the University of Rochester. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.
Time response of a type IIa natural diamond photoconductor to long-pulse low-intensity soft x rays
Authors: Coleman J. W. , Lierzer J. R. , Petrasso R. D.
Published: July 2002

For the study of soft x rays from plasmas and laser-plasma interactions, type IIa diamond photoconductor detector (PCD) is an important diagnostic for emissions from z pinches, [R. B. Spielman, Rev. Sci. Instrum. 63, 5056 (1992)], synchrotons, and laser-produced plasmas [D. R. Kania et al., Rev. Sci. Instrum. 61, 2765 (1990)]. Among diamond’s advantages are its time response (in the picosecond-to-nanosecond range for high-intensity fast pulses of soft x rays [D. R. Kania et al., J. Appl. Phys. 68, 124 (1990)]), and its band gap of 5.45 eV (which reduces its visible and near-uv sensitivity to near zero). We have investigated type IIa PCD using low-intensity slow pulses generated by a pulsed e beam hitting a copper target, with repetitions up to 50 kHz. The time response in this case is presented, leading to a proposal for a new type of diamond PCD for tokamaks, where the single detector has an array capability for position sensing and energy analysis.
Reciprocity in magnetic force microscopy
Authors: Wright C. D. , Hill E. W.
Published: July 2002

A theoretical treatment for contrast formation in the magnetic force microscope is given which relies on calculation of the force acting on the sample, rather than the more usual method which calculates the force acting on the microscope tip. The equivalence of this reciprocal force method is demonstrated by calculating the theoretical image for longitudinal step and arctangent magnetization transitions in thin-film recording media. The reciprocal force approach leads naturally to unambiguous definitions for the resolution of the magnetic force microscope and it is shown that conventional resolution measures, such as impulse response, line-spread function and step response, used in many other forms of microscopy, may be readily applied to the magnetic force microscope.
Design of improved electric potential fluctuation detector for 2 MeV heavy ion beam probe on TEXT (abstract)
Authors: Russell W. G. , Schoch P. M. , Crowley T. P. , Schatz J. G.
Published: July 2002

The present detector system used for the TEXT heavy ion beam probe (HIBP) is not sensitive to potential fluctuations of magnitude below 10−5×Vacc where Vacc is the accelerator voltage. With the upgrade of the TEXT HIBP to 2 MeV, the minimum detectable fluctuation is on the order of 10 V under optimum conditions. A new detector system has been proposed, and a proof-of-concept experiment has indicated that it should be sensitive to fluctuations on the order of 1 V. The new system separates the ion beam entering the energy analyzer into ten smaller beams. The fluctuations in each smaller beam are measured individually, effectively increasing the signal by a factor of 10 without increasing detector noise. A version of the new detector system is presented that is designed specifically for the high-energy analyzer of the 2 MeV TEXT HIBP. In addition to the improved detector set, this design includes a standard detector set for side-by-side comparison, as well as for measuring other plasma parameters.
Microwave scattering diagnostic on the Advanced Toroidal Facility torsatron (abstract)a)
Authors: Shats M. G. , Likin K. M. , Wilgen J. B. , Harris J. H. , Sarksyan K. A. , Baylor L. R. , Bell J. D. , Bigelow T. S. , Dunlap J. L. , Goldfinger R. C. , Ma C. H.
Published: July 2002

A 2 mm scattering diagnostic used to study density fluctuations of the electron cyclotron resonance heated plasma in the Advanced Toroidal Facility is described. A four-channel flexible antenna design was chosen to monitor fluctuations within the wave number range of 3<k⊥<20 cm−1 and to locate the scattering volume anywhere in the stellarator minor cross section. Special attention was paid to the system calibration and to the normalization of the k spectra. Analysis of the diagnostic noise showed that the main source of spurious signal was a scattering from high-level edge turbulence driven by the second-harmonic radiation from the gyrotron used for plasma heating. This spurious signal was suppressed using waveguide filters and rearrangement of the microwave circuit elements. Evidence in support of direct scattering from a well-defined plasma volume was found. Good correlation of the scattered waves’ intensity with the density scale length was observed. Use of a dual-homodyne circuit configuration made is possible to determine that the plasma density fluctuations were propagating in the electron diamagnetic direction.
Enhanced spatial localization of collective scattering measurements in the DIII-D tokamak
Authors: Rettig C. L. , Doyle E. J. , Peebles W. A. , Burrell K. H. , Groebner R. J. , Osborne T. H. , Luhmann N. C.
Published: July 2002

Collective scattering measurements on DIII-D have been complicated by significant toroidal and poloidal plasma rotation which produces large and inhomogeneous radial electrical fields which in turn Doppler shift the spectra of the scattered radiation. From independent measurements of the radical electric field profile, the radial variation of the fluctuation magnitude can be approximated from the frequency spectrum of the scattered radiation so the improved resolution is related to the scale length of the radial electrical field. Such improved spatial resolution will allow the interaction between local gradients and the fluctuation level to be investigated in more detail.
Horizontal-view interferometer on TEXT-Upgrade
Authors: Jiang Y. , Brower D. L.
Published: July 2002

The first experimental results from the horizontal-view, multichannel, heterodyne FIR interferometer system on TEXT-Upgrade are reported. The initial system employs parabolic beam-expansion optics and a 15 cm array with minimum channel spacing of 1.5 cm. Profiles of the plasma electron density will be presented. In addition, small-amplitude density perturbations resulting from sawteeth and tearing modes are examined. Due to the double pass of the laser beam through the plasma and the large distance of the detector array (2.5 m) from the plasma, refractive effects can be important. A ray tracing code is developed to correct the measured profiles.
Development of inside launch reflectometer systems on the DIII-D tokamak (abstract)a)
Authors: Doyle E. J. , Rhodes T. L. , Doane J. L. , Peebles W. A.
Published: July 2002

Inside launch (high field side) reflectometry is necessary for routine core access on DIII-D and is a very attractive option for ITER and TPX. For high temperature reactor relevant plasmas, relativistic corrections for the left-hand cutoff (inside launched) are relatively small, whereas these substantially affect the location of the normal right hand cutoff. On DIII-D, core access using the right hand cutoff is restricted to low density plasmas, while O-mode polarization is incompatible with flat H-mode density profiles. Routine core access can, however, be obtained using the left-hand cutoff and inside launch. On ITER and TPX, outside launch X-mode systems need to operate at high frequency, ∼100–250 GHz, such that the left-hand cutoff, which is at much lower frequency, ∼0–75 GHz, is an attractive option for high density operation. In addition, inside launch reflectometry can be used to investigate plasma asymmetries; on DIII-D an inboard/outboard asymmetry in turbulence response is observed at the L-H transition. An upgraded inside launch reflectometer system was recently installed on DIII-D, specifically to investigate the use of the left hand X-mode cutoff and inside launch for profile and turbulence measurements in reactor relevant plasmas. This system will also provide routine core access for reflectometry on DIII-D.
Comparative study of x-ray sources characterizing x-ray instrumentation
Authors: Li C. K. , Petrasso R. D. , Wenzel K. W. , Lo D. H. , Borrás M. C.
Published: July 2002

A study of x-ray sources for the purpose of characterizing x-ray instrumentation is presented. Specifically, in the soft x-ray wavelength region, we compare a proton-induced x-ray emission (PIXE) source to a conventional electron-beam x-ray source, and to a radioactive α fluorescence x-ray source. We find that PIXE has intense line radiation with respect to background continuum [C. K. Li et al., Rev. Sci. Instrum. 63, 4843 (1992)]. This desirable feature, as well as others, will make PIXE potentially a useful tool for characterizing x-ray detectors, optics, and filter.
High-resolution measurement of the He-β spectra of heliumlike chromium for possible diagnostic of laser-produced plasmas
Authors: Decaux V. , Beiersdorfer P. , Elliott S. , Osterheld A. , Clothiaux E.
Published: July 2002

High-resolution He-β spectra of heliumlike chromium have been recorded in an effort to provide accurate atomic data useful for the development of diagnostics of the electron temperature and density for laser-produced plasmas. The He-β spectra are of particular interest for these very-high-density plasmas (ne≥1024 cm−3) because, unlike the He-α and Ly-α transition, they are optically thin and can be used to determine the parameters of the compressed fuel. In addition, high-Z elements such as chromium will be needed for higher-temperature plasmas to be produced in future laser facilities. The present measurement was performed on the Livermore electron-beam ion trap with a low electron density ne≤5×1012 cm−3 and is used to calibrate in the low-density limit the theoretical calculations employed in modeling the high-ne spectra.
Characterization of Nova plasmas using an x-ray spectrometer with temporal and spatial resolution
Authors: Back C. A. , Kauffman R. L. , Bell P. M. , Kilkenny J. D.
Published: July 2002

Spectroscopic diagnostics have great potential to obtain high temperature measurements of plasmas created in inertial confinement fusion targets. The plasmas may be over 1 mm in size and therefore, one of the first steps in making better spectroscopic measurements has been to develop a spectrograph which takes advantage of gated technology by coupling a Bragg crystal to a microchannel plate. The crystal disperses the x rays, while slits add the ability to image the plasmas in the perpendicular direction. The characteristics of this diagnostic, TSPEC, are evaluated for laser-produced plasmas. Recent data will be presented from colliding plasmas and large-scale hohlraums which indicate that imaging can greatly enhance the ability to diagnose these plasmas.
Comparison of phosphors for broadband plasma emission detectors
Authors: Zurro B. , Ibarra A. , McCarthy K. J. , Acuña A. U. , Sastre R.
Published: July 2002

A comparative study of several luminescent materials which have potential interest for broadband plasma radiation detectors covering the vacuum ultraviolet (VUV) and x-ray ranges has been carried out. Among the studied phosphors Y2O2S:Tb (P-45) exhibits the highest sensitivity, which has been seen to be more than one order of magnitude higher than the standard VUV phosphor-sodium salicylate, over the whole spectral range.