bluuebunny/crossref_metadata_2025 huggingface dataset:
High sensitivity mass spectrometer system for contaminant measurement in high purity gases
Authors: Ma Y. , Liu B. Y. H. , Lee H. S. , Mauersberger K. , Morton J.
Published: July 2002

A mass spectrometer beam system using a double focusing sector analyzer and an electron impact ion source has been developed for trace analysis. The molecular beam, formed through a focusing glass capillary array, serves as the gas inlet of the system. Closed cycle cryopumps and ion pumps are used to generate the high vacuum. System roughing is achieved using sorption pumps. Clean and oil free vacuum was obtained by nonmechanical pumping. System normal mode sensitivity is about 107 counts/s/Torr. System low pressure mode sensitivity can be three orders of magnitude higher when sample pressures are below 30 mTorr. A parts-per-billion range system detection capability was accomplished. Slow response time for adsorptive species measurements is a major drawback of the sample inlet system.
Vibrating wire magnetic susceptometer
Authors: Asti G. , Solzi M.
Published: July 2002

The growing interest in the field of nanoscale magnetic systems, especially regarding thin films and multilayers, emphasizes the need for sensitive measurement techniques. A new type of magnetic susceptometer, based on an alternative field gradient, is described. The mechanical resonating element is a long, thin, metallic wire. A complementary component generates a large local field gradient while keeping the field intensity as low as possible. The basic configuration of a typical instrument is presented and a general theoretical treatment is given concerning the magnetic force, the mechanical sensitivity of the vibrating system, and the vibration sensor.
An optical interferometer for gas bubble measurements
Authors: Gelmetti Andrea , Bellini Tommaso , Lago Paolo , Corti Mario
Published: July 2002

A compact and stable interferometer for the measurement of the radius of a gas bubble in a liquid is described. The system combines a very high sensitivity in radius change measurements (1 Å) with a good determination of the absolute value of the radius itself.
Asymmetric 2-bounce monochromator for quasi-fixed offset
Authors: Schildkamp W. , Meron M.
Published: July 2002

In many monochromatic x-ray applications, it is important to maintain a constant direction of the monochromatized beam, preferably parallel to the direction of the original beam. For the most exacting applications, independent-crystal two-bounce monochromators can be used. These however, are costly and cumbersome. Therefore, in less demanding situations or when space is at premium, two-bounce channel-cut monochromators are commonly used. Unfortunately, while the direction of the beam emerging from a channel-cut monochromator is fixed, the beam offset varies with the angle of incidence, i.e., with the energy of the monochromatic beam. This complicates experiments in which it is important to maintain the beam on a fixed spot of the sample. We show, however, that the variation of beam offset in channel-cut monochromators can be greatly reduced by introducing a small amount of asymmetry into the cut. The exact amount of asymmetry (typically a few degrees) depends, of course, on the crystal and the energy range. We will present a full mathematical analysis and a design of a working monochromator based on this scheme.
Advances in temperature derivative control and calorimetry
Authors: Hemmerich J. L. , Loos J.-C. , Miller A. , Milverton P.
Published: July 2002

Temperature stabilization by inertial feedback control has proven a powerful tool to create the ultrastable environment essential for high resolution calorimetry. A thermally insulated mass, connected to a base through Seebeck effect sensors (thermopiles) is used as a reference to control the base temperature. The thermopile signal is proportional to both the heat capacity of the reference mass and the derivative Θ̇ of the base temperature Θ. Using vacuum insulation and bismuth telluride thermopiles, we designed and tested temperature derivative sensors (TDSs) with sensitivities up to 3300 V s K−1. Standard industrial controllers with approximately ±1 μV input noise and stability, permit control of temperature derivatives to ±3×10−10 K s−1. Single-cup thermoelectric calorimeters coupled to the TDS-controlled base permitted measurement of heat flow from samples in a power range from 3 μW to 10 W with high accuracy (±100 ppm), resolution (±0.2 μW), and reproducibility (±1 μW). The design of two instruments is described in detail. Their performance is demonstrated on a variety of measurements, e.g., the determination of sample heat capacities with temperature ramp rates Θ̇=±5×10−6 K s−1, the half-life of a 3 g tritium sample in a uranium getter bed, the decay heat of depleted uranium, and the heat evolution of epoxy resin.
EUV and soft x-ray transmission microscope (abstract)
Authors: Watts R. N. , Lucatorto T. B. , Liang S. T. , Polack F. , Scheinfein M. R.
Published: July 2002

We present preliminary performance results for a new type of imaging microscope operating in the EUV and soft x-ray regions. This microscope is a true transmission microscope in which an unmagnified image of the sample is formed by differential absorption of the x-ray beam as it passes through the sample. The unmagnified photon image is converted into low energy secondary electrons at a thin CsI photocathode, and the subsequent electron pattern is magnified and imaged using a simple 3-lens system. Conversion of the magnified electron patern into visible photons occurs at a fine grain phosphor viewed by a CCD detector/computer combination that allows parallel detection of the original photon image in near real time with approximately 1000× magnification. The microscope has a theoretical resolution of 20 nm and a potentially wide range of uses including biology, materials science studies, and investigations into magnetic dichroism effects. The design and preliminary imaging results of the microscope will be presented and future directions discussed.
Pixel array detector for time-resolved x-ray scattering (invited)
Authors: Rodricks Brian G. , Barna Sandor L. , Gruner Sol M. , Shepherd John A. , Tate Mark W. , Wixted Robert L.
Published: July 2002

This paper describes the development of a large area hybrid pixel detector designed for time-resolved synchrotron x-ray scattering experiments in which limited frames, with a high framing rate, are required. The final design parameters call for a 1024×1024 pixel array device with 150-micron pixels that is 100% quantum efficient for x-rays with energy up to 20 keV, with a framing rate in the microsecond range. The device will consist of a fully depleted diode array bump bonded to a CMOS electronic storage capacitor array with eight frames per pixel. The two devices may be separated by a x-ray blocking layer that protects the radiation-sensitive electronics layer from damage. The signal is integrated in the electronics layer and stored in one of eight CMOS capacitors. After eight frames are taken, the data are then read out, using clocking electronics external to the detector, and stored in a RAM disk. Results will be presented on the development of a prototype 4×4 pixel electronics layer that is capable of storing at least 10,000 12-keV x-ray photons for a capacity of over 50 million electrons with a noise corresponding to 2 x-ray photons per pixel. The diode detective layer and electronics storage layer along with the radiation damage and blocking layers will be discussed.
Double-crystal monochromator as the first optical element in BESSRC-CAT beamlines (abstract)
Authors: Beno Mark A. , Ramanathan Mohan
Published: July 2002

The first optical element in the BESSRC-CAT beamlines at the Advanced Photon Source will be a monochromator, so that a standard design for this critical component is advantageous. The monochromator we have designed is a double-crystal, fixed-exit scheme with a constant offset designed for UHV operation, thereby allowing windowless operation of the beamlines. The crystals are mounted on a turntable with the first crystal at the center of rotation. A mechanical linkage is used to correctly position the second crystal and maintain a constant offset. The main drive for the rotary motion is provided by a vacuum-compatible Huber goniometer isolated from the main vacuum chamber. Rotary motion of the primary monochromator stage is accomplished by using two adjacent vacuum chambers connected only by the small annular opening around a hollow stainless steel shaft, which connects the Huber goniometer to the turntable on which the crystals are mounted. The design of the monochromator is such that it can accommodate both water and liquid nitrogen cooling for the crystal optics. The basic design for the monochromator linkage mechanism will be presented along with details of the monochromator chamber. The results of initial optical tests of the monochromator system using tilt sensors and a precision autocollimator will also be given.
Operational experience at the Advanced Light Source (invited)
Authors: Jackson Alan
Published: July 2002

The Advanced Light Source (ALS) has been operational for users since October 1993 when white light from a bend magnet was delivered to the Center for X-Ray Optic’s (CXRO) x-ray microprobe end station. Since then, the ALS has installed and commissioned three undulators and their beamlines (including monochromators and post-monochromator focusing optics), and eight bend-magnet beamlines, including one dedicated to machine diagnostics. Apart from one serious outage, when scheduled beam was not available to users for 17 days, the ALS has enjoyed remarkable operating statistics, with typically 95% of scheduled beam time delivered to the users. Beam quality has also been very good. With a vertical emittance measured at 0.06 nm-rad, the electron beam is kept stable to about one-tenth of its transverse dimensions, in the face of changing error fields in the insertion devices (as their main fields are varied), temperature variations, and floor vibration. The longitudinal motion of the beam, which leads to an increase in the electron beam energy spread and thence to a degradation of the undulator spectra, has recently been brought under control by the addition of an innovative feedback system. This paper focuses on those aspects of electron beam stability that we find most affect the ALS users: beam size and position, and energy spread.
Plans for conversion of SURF II to SURF III (abstract)
Authors: Hamilton A. D. , Furst M. L. , Hughey L. R. , Madden R. P. , O’Brian T. R. , Proctor J. E.
Published: July 2002

The Synchrotron Ultraviolet Radiation Facility (SURF II) at the National Institute of Standards and Technology, Gaithersburg, MD, USA, has served as a primary radiometric standard in the vacuum ultraviolet region since its conversion from a synchrotron to an electron storage ring in 1974. The magnet iron, however, dates back to an original betatron design of the late 1940s. The advent of both modern materials and methods of finite element analysis have made possible the design of magnets offering far greater dc performance than the existing SURF system. In this paper we discuss the general design and plans to convert SURF II to SURF III, which will offer reduced radiometric uncertainty, an increase in energy from 300 MeV to 385 MeV, a modernized control system, and two new beamlines, which are not presently possible. Anticipated new beamline activities include a substantial new effort devoted to radiometric improvements from IR to far UV and development of stations for microspectoscopy and electroreflectance.
Why cryogenically cooled, thin crystals handle extremely high power densities
Authors: Knapp G. S. , Jennings G. , Beno M. A.
Published: July 2002

Recently, a new type of cryogenically cooled high heat load monochromator was proposed [Knapp et al., Rev. Sci. Instrum. 65, 2792 (1994)] and developed at Argonne National Laboratory [Knapp et al., Rev. Sci. Instrum. 66, 2138 (1995)] and tested [Rogers et al., Rev. Sci. Instrum. 66, 3494 (1995)] at the European Synchrotron Radiation Facility (ESRF). These tests showed that powers of 153 W and power densities of 450 W/mm2 cause only negligible strain. These powers and power densities are larger than will be absorbed by the first crystal on an undulator beamline at the Advanced Photon Source (APS). In our earlier work, we suggested that the crystal might show strain at much lower values of the powers and power densities. We now can explain the ESRF results in terms of the unique role the negative thermal expansion coefficient of Si plays in minimizing strain.
Magnet system of the SPring-8 booster synchrotron
Authors: Yonehara H. , Suzuki H. , Ueyama Y. , Aoki T. , Fukami K. , Tani N. , Hayashi S. , Kaneta T. , Abe H. , Okanishi K. , Ohtsuchi S. , Hosoda N. , Hirata Y. , Nagafuchi T. , Chugun T. , Kubo H. , Yokomizo H.
Published: July 2002

The construction of the SPring-8 booster synchrotron was started in 1993. The synchrotron has a two-fold symmetric lattice composed of 40 FODO cells. There are 30 normal cells and 2 straight sections, and it is composed of 64 bending magnets. The integral values of the magnetic field of the bending magnets were measured, and adequate results were obtained. The power supply of the bending magnets, which must be operated following a trapezoidal excitation-curve of the output current, is being constructed and tested now. This report presents the results of the integral values of the magnetic field of the bending magnets and the excitation-curve measurement of the power supply.
A new compact double crystal monochromator for high energy synchrotron radiation and ultrahigh vacuum operation
Authors: Middleton F. H. , Emmel G. R. , Feyzi F. , Gregerson G. M.
Published: July 2002

The UW-Madison Physical Sciences Laboratory proposed a unique double crystal monochromator to the Advanced Photon Source and UNI-CAT that has resulted in two development projects for the instrument. These two very similar designs are capable of accepting inclined geometry, other high heat load optics, and sagittal focusing crystals by provisions of ample space for such optical elements. The monochromator is a compact instrument. It has a single rotational stage that does not require a track system to access the crystals yet will fit in the confined back space at APS by having only 300 mm distance between the beam centerline and back of the instrument. The frame footprint is only 0.74 m x 0.84 m. The instrument is truly UHV rated for vacuum in the 1.0E−10 Torr range by virtue of its unique internal mechanisms for linear positioning and rotational adjustment of crystals. The design may be modified for operation at low energy synchrotron radiation in the 0.8 to 4.0 keV range requiring higher Bragg angles.
A high-temperature octopole ion guide for measuring absolute cross sections of ion–metal atom reactions
Authors: Levandier Dale J. , Dressler Rainer A. , Murad Edmond
Published: July 2002

We describe in detail a high-temperature octopole/collision cell apparatus for studying ion–molecule reactions involving nonvolatile target species, including metals. The system can be operated at temperatures up to ∼1200 K and features coaxially heated octopole rods and a heated collision cell in which the vapor of a nonvolatile target material is generated by evaporation from a bulk sample contained therein. The poles are heated independently of the cell and are maintained at a higher temperature to prevent condensation of the sample on the poles. This ensures a well characterized operating temperature that is necessary for absolute cross-section measurements. The apparatus design permits two independent methods for the determination of the target vapor density. The absolute Na+N2+ charge transfer cross section has been measured for collision energies in the range 0.1–2.25 eV. These results represent the first guided-ion beam measurement of an absolute ion–metal atom reaction cross section, and are compared to earlier studies conducted with other methods.
Monolithic nonlinear transmission lines for ultrashort and moderate pulse reflectometry (abstract)
Authors: Zhang W.-M. , Hsia R. P. , Chen Z.-T. , Jiang F. , Domier C. W. , Luhmann, Jr. N. C.
Published: July 2002

Monolithic nonlinear transmission lines can be employed as ultrashort pulse (1–5 ps rise/fall time) generators to extend ultrashort pulse reflectometry (USPR) to high field tokamaks such as TFTR, Alcator C-MOD, and ITER. Multiple barrier varactor devices have been successfully employed as high power and high speed devices in this application. Monolithic NLTLs can also be employed to simplify moderate pulse reflectometry systems, in which NLTLs may be employed as broadband frequency multipliers. Theoretical and experimental investigations will be presented.
Transmission line studies for ITER compatible reflectometers
Authors: Wagner D. , Kasparek W. , Gantenbein G. , Manso M. E. , Sanchez J. , Donné A. J. H.
Published: July 2002

Corrugated circular transmission lines are considered as high performance, low loss, broadband lines for reflectometry on ITER. These lines are proposed as a possible solution for the equatorial low-field-side system and as a part (receiver-vacuum vessel) of the transmission lines for the high-field side and the out-of-midplane reflectometer system, because of their restricted access. Theoretical and experimental studies show the good properties of these lines: low losses, a smooth characteristic transmission, and a very low level of parasitic reflections. Quasioptical systems are also proposed as a solution for the coupling of several microwave emitter receivers, working in a fundamental waveguide, into a single broadband corrugated line.
Determination of internal radio frequency electric field profiles via millimeter wave reflectometry in the DIII-D Tokamak
Authors: Lee J. H. , Doyle E. J. , Luhmann, Jr. N. C. , Peebles W. A. , Petty C. C. , Pinsker R. I. , Rhodes T. L.
Published: July 2002

Millimeter wave reflectometry was employed to determine radio frequency wave electric field profiles in the DIII-D Tokamak. The method utilizes spatially localized X-mode reflectometer measurements in the 65–73 GHz frequency range to detect coherent fluctuations in magnetic field and density driven at the fast magnetosonic wave (FW) frequency (60 MHz). The FW electric field profiles were determined by adopting a geometric optics approach, which is appropriate for interpreting reflectometer data where the perturbing wavelength is longer than the probing wavelength. Successful measurements from this system were utilized to investigate FW propagation effects on DIII-D. The FW launch directionality necessary for current drive was confirmed at a position toroidally close to the FW antenna.
Neutron diagnostics in compact helical system
Authors: Isobe M. , Sasao M. , Osakabe M. , Fujita J. , Okamura S. , Kumazawa R. , Minami, T. , Matsuoka K. , Takahashi C.
Published: July 2002

An efficient neutron diagnostic system has been established and applied to deuterium experiments on compact helical system. A neutron counter was installed at the center of the torus, and the detection efficiency was about two orders of magnitude higher than the values of most toroidal fusion devices. The effect of the stray magnetic field on the operation of a proportional counter was experimentally confirmed to be negligibly small. The ion temperature, as low as 400 eV, was obtained from neutron measurement with a time resolution of 1 ms. The decay time of neutron emission rate after the termination of a 1% deuterium-doped beam was measured and the confinement time of neutral beam-injected fast ions was estimated. The fast ion confinement was clearly improved by strengthening the toroidal magnetic field.
Calibration issues of the Tokamak Fusion Test Reactor multichannel neutron collimator
Authors: von Goeler S. , Johnson L. C. , Bitter M. , Efthimion P. C. , Roquemore A. L.
Published: July 2002

The calibration procedures for the detectors in the neutron collimator are reviewed. The absolute calibration was performed for the NE451 detectors, in situ, by moving a DT neutron generator in the Tokamak Fusion Test Reactor (TFTR) vacuum vessel across each sight line. This calibration was transferred to other detectors in the same channel. Four new sight lines have been installed at a different toroidal location, which view the plasma through the vacuum vessel port cover rather than through thinned windows. The new detectors are cross calibrated to the NE451 detectors with a “jog shot” procedure, where the plasma is quickly shifted in major radius over a distance of 30 cm. The jog shot procedure shows that scattered neutrons account approximately for 30% of the signal of the new central channels. Corrections for detector nonlinearity are discussed. The neutron source strength from the collimator agrees within 10% with the source strength from global neutron monitors in the TFTR test cell.
Design of radial neutron spectrometer array for the International Thermonuclear Experimental Reactor
Authors: Nishitani T. , Kasai S. , Iguchi T. , Takada E. , Ebisawa K. , Kita Y.
Published: July 2002

We designed the radial neutron spectrometer using a new type DT neutron spectrometer base on a recoil proton counter-telescope technique aiming ion temperature measurement for the International Thermonuclear Experimental Reactor (ITER). The neutron spectrometer will be installed on the well collimated neutron beam line. A large area recoil proton emitter is placed parallel to the incident neutron beam and microchannel collimating plates are inserted between the radiator and the recoil proton detectors away from the neutron beam in order to limit the scattering angle of protons to the proton detectors. Here a very thin polyethylene film and a silicon surface barrier detector are employed as the radiator and proton detector, respectively. The energy resolution and detection efficiency are estimated to be 2.5% and 1×10−5 counts neutron−1 m2, respectively, for the DT neutron through Monte Carlo calculations. Five units of the spectrometers will be installed just outside the biological shield, will include a fan array using penetrations inside the bioshield and a precollimator in the horizontal port. The lifetime of the proton detectors is estimated to be about one year in the basic performance phase of ITER by neutron transport calculations using the Monte Carlo neutron and photon transport code (MCNP).
Tritium to deuterium ratio measurement by collective Thomson scattering
Authors: Richards R. K. , Hutchinson D. P. , Ma C. H.
Published: July 2002

A technique is proposed for the determination of the tritium to deuterium density ratio in ITER using collective Thomson scattering at a wavelength of 10 μm. The measurement is made by viewing the component of scattered laser power nearly perpendicular to the magnetic field giving rise to ion cyclotron modulation of the scattered spectrum. The tritium/deuterium ratio may be inferred by a deconvolution of the scattered laser power. Due to the narrow bandwidth of the scattered signal and the spatially varying magnetic field, a narrowband heterodyne imaging array receiver will be required to observe the scattered spectrum.
Multipass/multipulse Thomson scattering on CDX-U (abstract)
Authors: Stutman D. , Hwang Y. S. , Menard J. , Choe W. , Ono M. , Petrov Y. , Gusev V. , Mukhin E.
Published: July 2002

A multipass/multipulse Thomson scattering system has been implemented on CDX-U in collaboration with the Ioffe Institute, St. Petersburg. The system consists of a low energy (1.5– 2.5 J), passively Q-switched ruby laser, and a multipass optical cavity enclosing the plasma. Multiple reflections of the beam within the cavity increase by about an order of magnitude the number of scattered photons, allowing temperature density to be measured with good accuracy even at very low plasma density. By feeding the returned beam back into the laser, the system can deliver several pulses over a 1 ms period. However, the experiments on CDX-U show that a mechanical shock wave reaching the multipass system affects the feedback and laser output per pulse drops significantly. Therefore we operate the system by fine tuning the laser cavity, so that output is practically independent of feedback from multipass cavity. Also, by optimizing the transmission of the passive Q-switch and the pumping power, we obtain that laser output is concentrated in single large pulse of 2–2.5 J energy. We achieve circulating energy in the plasma in excess of 12 J per pulse, while minimizing at the same time stray light. As shown by results from CDX-U, this enables in some cases better than 10% accuracy, despite relatively low plasma density conditions.
Initial operation of the divertor Thomson scattering diagnostic on DIII–D (abstract)
Authors: Carlstrom T. N. , Hsieh C. L. , Stockdale R. , Nilson D. G. , Hill D. N.
Published: July 2002

The first Thomson scattering measurements of ne and Te in the divertor region of a tokamak are reported. These data are used as input to boundary physics codes such as UEDGE and DEGAS and to benchmark the predictive capabilities of these codes. These measurements have also contributed to the characterization of tokamak disruptions. A Nd:YAG laser (20 Hz, 1 J, 15 ns, 1064 nm) is directed vertically through the lower divertor region of the DIII–D tokamak. A custom, aspherical collection lens (f/6.8) images the laser beam from 1 to 21 cm above the target plates into eight spatial channels with 1.5 cm vertical and 0.3 cm radial resolution. Two-dimensional mapping of the divertor region is achieved by sweeping the divertor X-point location radically through the fixed laser beam location. Fiber optics carry the light to polychromators whose interference filters have been optimized for low-Te measurements. Silicon avalanche photodiodes measure both the scattered and plasma background light. Temperatures and densities are typically in the range of 5–200 eV and 1–10×1019 m−3, respectively. Low temperatures, Te<1 eV, and high densities, ne>8×108 cm−3 have been observed in detached plasmas. Background light levels have not been a significant problem. Reduction of the laser stray light permits Rayleigh calibration. Because of access difficulties, no in-vessel vacuum alignment target could be used. Instead, an in situ laser alignment monitor provides alignment information for each laser pulse. Results are compared with Langmuir probe measurements where good agreement is found except for regions of high ne and low Te as measured by Thomson scattering.
A prototype imaging second harmonic interferometer
Authors: Jobes F. C. , Bretz N. L.
Published: July 2002

We have built a prototype imaging second harmonic interferometer, which is intended to test critical elements of a design for a tangential array interferometer on C-Mod6. The prototype uses a pulsed, 35 mJ, 10 Hz multimode, Nd:YAG laser, LiB3O5 doublers, a fan beam created by a cylindrical lens, four retroreflector elements, and a CCD camera as a detector. The prototype also uses a polarization scheme in which the interference information is eventually carried by two second harmonic beams with crossed polarization. These are vector summed and differenced, and separated, by a Wollaston prism, to give two spots on the CCD. There is a pair of these spots for each retroreflector used. The phase information is directly available as the ratio of the difference to sum the intensities of the two spots. We have tested a single channel configuration of this prototype, varying the phase by changing the pressure in an air cell, and we have obtained a 5:1 light to dark ratio, and a clear sinusoidal variation of the ratio as a function of pressure change.
A high sensitivity two-color interferometer for pulsed power plasmas (abstract)
Authors: Weber B. V. , Fulghum S. F.
Published: July 2002

A high sensitivity, high bandwidth, two-color interferometer (1064 and 532 nm) has been tested on the Hawk pulsed power generator at the Naval Research Laboratory. The phase resolution is 10−5 waves with a rise time of 3 ns, a new capability for diagnosing plasmas, and neutrals in pulsed power experiments. The two-color feature is used to distinguish phase shifts from free (plasma) electrons and bound (neutral and ion) electrons. Simultaneous electron and neutral density measurements were demonstrated in a plasma opening switch (POS) experiment. The ability to measure small phase shifts with fast rise time were demonstrated in a plasma filled diode experiment. The high sensitivity and vibration isolation enable neutral gas distribution measurements from supersonic nozzles used in plasma radiation source experiments. Examples of these measurements and future applications are described.
X-ray spectroscopy of plasmas created by the Nike KrF laser
Authors: Aglitskiy Y. , Lehecka T. , Deniz A. , Hardgrove J. , Seely J. , Brown C. , Feldman U. , Pawley C. , Gerber K. , Bodner S. , Obenschain S. , Lehmberg R. , McLean E. , Pronko M. , Sethian J. , Stamper J. , Schmitt A. , Sullivan C. , Holland G. , Laming M.
Published: July 2002

The x-ray emission from plasmas created by the Naval Research Laboratory Nike KrF laser was characterized using spectroscopic instruments. The targets were thin foils of aluminum and titanium and were irradiated by laser energies in the range 100–1500 J. Using a spherical-crystal imaging spectrometer operating in the 1–2 keV x-ray region, the density, temperature, and opacity of aluminum plasmas were determined with a spatial resolution of 10 μm in the direction perpendicular to the target surface. The spectral line ratios indicated that the aluminum plasmas were relatively dense, cool, and optically thick near the target surface.
Target-induced damage considerations in the design of ICF diagnostics (abstract)
Authors: Turner R. E. , Anderson A. T. , Estabrook K. , Gerassimenko M. , Serduke F. J. D.
Published: July 2002

We have recently performed an empirical study of issues associated with target-induced damage, with emphasis on the next-generation NIF target chamber. However, some conclusions are also applicable to present day experimental diagnostics. We will discuss three topics: (1) degradation of the diagnostic due to the buildup of unwanted materials; (2) physical damage to the diagnostic from target debris; and (3) the potential for the diagnostic to create debris, which can cause subsequent damage to chamber optics. In the first category, we have measured both target material (Au,Cu) and ablated diagnostic material (Ta, Pb) which has subsequently redeposited on x-ray filters, changing their opacity. We have also measured the deposition of Al, from x-ray ablation from a nearby mounting fixture, onto a fused silica optic. Damage to diagnostics on Nova, sufficient to result in their failure, tends to be restricted to that caused by nonvaporized debris from large copper shields, gas fill tubes, etc. However, NIF targets will have a significantly larger impulse associated with the expanding gold hohlraum. We have measured the impulse associated with Nova hohlraums, for benchmarking code calculations. We will briefly discuss the implications of the third category in the design of NIF diagnostics.
The high resolution video capture system on the alcator C-Mod tokamak
Authors: Allen A. J. , Terry J. L. , Garnier D. , Stillerman J. A. , Wurden G. A.
Published: July 2002

A new system for routine digitization of video images is presently operating on the Alcator C-Mod tokamak. The PC-based system features high resolution video capture, storage, and retrieval. The captured images are stored temporarily on the PC, but are eventually written to CD. Video is captured from one of five filtered RS-170 CCD cameras at 30 frames per second (fps) with 640×480 pixel resolution. In addition, the system can digitize the output from a filtered Kodak Ektapro EM Digital Camera which captures images at 1000 fps with 239×192 resolution. Present views of this set of cameras include a wide angle and a tangential view of the plasma, two high resolution views of gas puff capillaries embedded in the plasma facing components, and a view of ablating, high speed Li pellets. The system is being used to study (1) the structure and location of visible emissions (including MARFEs) from the main plasma and divertor, (2) asymmetries in gas puff plumes due to flows in the scrape-off layer (SOL), and (3) the tilt and cigar-shaped spatial structure of the Li pellet ablation cloud.
Nuclear diagnostics in support of inertial confinement fusion experiments (invited)
Authors: Moran M. J. , Hall J.
Published: July 2002

As the yields of inertial confinement fusion (ICF) experiments increase to National Ignition Facility levels new diagnostic techniques for studying details of fusion burn behavior will become feasible. The new techniques will provide improved measurements of fusion burn temperature and history. Improved temperature measurements might be achieved with magnetic spectroscopy of fusion neutrons. High-bandwidth fusion reaction history will be measured with fusion-specific γ-ray diagnostics. Additional energy-resolved γ-ray diagnostics might be able to study a selection of specific behaviors during fusion burn. Present ICF yields greater that 1013 neutrons are sufficient to demonstrate the basic methods that underlie the new techniques. As ICF yields increase, the diagnostics designs can be adjusted accordingly in order to provide clear and specific data on fusion burn performance.
Thomson scattering measurements in the RFX reversed field pinch
Authors: Bassan M. , Bilato R. , Giudicotti L. , Pasqualotto R. , Sardella A.
Published: July 2002

The first systematic measurements of the electron temperature (Te) spatial profile have been obtained in the reversed field pinch experiment RFX with a single pulse Thomson scattering (TS) diagnostic. Scattered light from a ruby laser pulse (E⩽15 J, Δt=30 ns) is collected through three objectives from 10 positions along a diameter in the plasma equatorial plane, with a spatial resolution of 2.5 cm. Plasma discharges with current in the range 700–900 kA have been investigated finding evidence of a quite flat Te profile. Data dispersion significantly greater than experimental uncertainties provides an indication of remarkable plasma fluctuations. Results are in good agreement with Te measurements from other single chord spectroscopic diagnostics (SiLi detector and SXR double filter), showing a reliable operation down to an electron density ne=3×1019 m−3. Integration of this apparatus with a ND:YLF laser system for multipulse Thomson scattering measurements, sharing the same input optics, is under way.
Data processing techniques for density profile evaluation from FM–CW reflectometry
Authors: Varela P. , Silva A. , Manso M. , Santos J. , Nunes F.
Published: July 2002

Microwave reflectometry is an important diagnostic to measure the plasma density profile on present fusion experiments and on next devices like ITER. Several data processing techniques, currently employed to evaluate the density profile, use filtering algorithms to overcome the effect of plasma fluctuations. However, in these processes the detailed profile structure may be altered or even lost. In order to study this problem we applied two different data analysis methods to experimental results obtained in ASDEX, when a locked magnetohydrodynamic mode is present. The first method uses a software implementation of a frequency discriminator to estimate continuously the evolution of the group delay versus frequency and the second applies a sliding fast Fourier transform method to determine an averaged group delay curve. It is shown that the profile exhibits a density plateau due to the magnetic island, which can be lost due to filtering or averaging procedures. Next we perform a numerical study for a profile with a small rotating density plateau, disturbed by random noise to simulate the effect of plasma fluctuations. The frequency discriminator is used to obtain group delay sweeps from consecutive sweeps and a two-dimensional (2-D) regularization technique is applied to the multiple samples. It is shown that the 2-D method has advantages in the routine evaluation of the detailed profile structure masked under the effect of plasma turbulence, due to the combined averaging (over space and time), based on the correlation between neighboring data points.
Neural network evaluation of tokamak current profiles for real time control (abstract)
Authors: Wróblewski Dariusz
Published: July 2002

Active feedback control of the current profile, requiring real-time determination of the current profile parameters, is envisioned for tokamaks operating in enhanced confinement regimes. The distribution of toroidal current in a tokamak is now routinely evaluated based on external (magnetic probes, flux loops) and internal (motional Stark effect) measurements of the poloidal magnetic field. However, the analysis involves reconstruction of magnetohydrodynamic equilibrium and is too intensive computationally to be performed in real time. In the present study, a neural network is used to provide a mapping from the magnetic measurements (internal and external) to selected parameters of the safety factor profile. The single-pass, feedforward calculation of output of a trained neural network is very fast, making this approach particularly suitable for real-time applications. The network was trained on a large set of simulated equilibrium data for the DIII-D tokamak. The database encompasses a large variety of current profiles including the hollow current profiles important for reversed central shear operation. The parameters of safety factor profile (a quantity related to the current profile through the magnetic field tilt angle) estimated by the neural network include central safety factor, q0, minimum value of q, qmin, and the location of qmin. Very good performance of the trained neural network both for simulated test data and for experimental data is demonstrated.
Data acquisition system for Alcator C-Mod
Authors: Fredian T. W. , Stillerman J. A. , Greenwald M.
Published: July 2002

The Alcator C-Mod experiment requires an efficient data handling system to acquire and distribute the large number of measurements recorded during each pulse of the tokamak. Over 2000 signals amounting to over 80 megabytes of data are stored and distributed to 40 workstations for display and analysis. With machine pulses occurring every 10 to 15 min, most of the information must be distributed within 2 to 3 min after the pulse to enable the experimentalist to adjust the control settings for the next pulse. In addition to the local control room data distribution requirements, the system must also provide data access to remote sites which monitor diagnostics installed on the Alcator C-Mod experiment. This article will describe the hardware and software used to accomplish data handling tasks.
Force measurement using vibrational spectroscopy
Authors: Johnson Ward , Alers G. A.
Published: July 2002

The stress dependence of ultrasonic velocities is used as the physical basis for a device that measures large forces. A solid aluminum cylinder serves as a load-bearing element, and noncontacting electromagnetic-acoustic transducers are used to excite and detect resonant vibrational modes. The problem of vibrational damping at the ends of the cylinder is solved by making the diameter slightly larger in a central section, so that certain resonant modes are “trapped,” with negligible amplitude at the ends. Nearly complete temperature compensation is achieved by taking the ratio of two resonant frequencies with approximately the same temperature dependence but with much different stress dependencies. The measurement of force with vibrational spectroscopy provides several advantages over conventional resistive strain gages, including greater resolution, insensitivity to transducer and bond degradation, durability in harsh environments, and insensitivity to bending moments. The resolution in strain is approximately 4×10−8. The upper limit of measurable stresses approaches the yield strength of the aluminum cylinder; this is approximately 325 MPa, which corresponds to a strain of 4×10−3.
A single, small particle launch system by electrothermal gun and microsabot
Authors: Yoshida Hiro , Hoshi Yoshinobu , Uematsu Kazuo , Kitazawa Yukihito
Published: July 2002

A new particle launch system for impact tests of materials without disturbing test environment, such as temperature and external loads, is developed. The system is composed of a electrothermal gun with 2.5 kJ power supply, sabot–particle separation unit, velocity measuring device, furnace, and tensile load unit. By using this system, single, small particle of milli- to submillimeter size is launched. In the present study a samarium–cobalt magnetic sphere is chosen as the impact particle because of the simplicity of the direct velocity measurement by the induction current method. The particle is installed on a microsabot of weight ranging from 70 to 220 mg. Temperature, tensile load, and particle velocity range, respectively, up to 1400 °C, 19 600 N, and 1000 ms−1. For sabot–particle separation, two configurations of tapered end and flat end sabot stoppers are tested. The main results are as follows: (1) The flat end sabot stopper is found out to be useful for the present velocity range. (2) An empirical formula of Vp=362PC0.5 m−0.5 is given, where Vp is particle velocity in ms−1, P is applied voltage in kV, C is capacity of the power supply unit in μF, and m is mass of the microsabot in mg. (3) Vp is not always the same as the sabot velocity in bore due to the sabot–particle separation process. (4) The separation process may cause appreciable rotations of the impact particle. This launch system can be applicable for the particle impact tests of ceramic materials held under elevated temperatures and external load condition.
Approach to a window coating problem by in situ transmission monitoring and laser blow-off cleaning developed in the JT-60U Thomson scattering system
Authors: Yoshida H. , Naito O. , Hatae T. , Nagashima A.
Published: July 2002

For solving a window coating problem, an in situ window transmission monitoring by inferring it precisely from a known attenuation of the deposited film has been developed in the JT-60U Thomson scattering system. Also the practicability of an in situ window cleaning based on a laser blow-off technique has been investigated extensively. The coated film composition could be guessed to be a resin such as polyacrylonitrile with a small amount of metals. The existence of chromatic upper limit has been found in the recovered transmission after the blow-off cleaning, which gives systematic errors only of less than 3% to an apparent measurement of both electron density and temperature at 10 keV or less. The attenuation itself is unchanged before and after the laser blow-off cleaning. A complementary use of both methods will provide the Thomson scattering measurement of high Te plasmas with durable reliability and sufficient precision in the existing tokamaks and the International Thermonuclear Experimental Reactor.
Absorption spectroscopy characterization measurements of a laser-produced Na atomic beam
Authors: Ching C. H. , Bailey J. E. , Lake P. W. , Filuk A. B. , Adams R. G. , McKenney J.
Published: July 2002

A pulsed Na atomic beam source developed for spectroscopic diagnosis of a high-power ion diode is described. The goal is to produce a ∼1012-cm−3-density Na atomic beam that can be injected into the diode acceleration gap to measure electric and magnetic fields from the Stark and Zeeman effects through laser-induced fluorescence or absorption spectroscopy. A ∼10 ns full width at half-maximum (FWHM), 1.06 μm, 0.6 J/cm2 laser incident through a glass slide heats a Na-bearing thin film, creating a plasma that generates a sodium vapor plume. A ∼1 μs FWHM dye laser beam tuned to 5890 Å is used for absorption measurement of the Na I resonant doublet by viewing parallel to the film surface. The dye laser light is coupled through a fiber to a spectrograph with a time-integrated charge-coupled-device camera. A two-dimensional mapping of the Na vapor density is obtained through absorption measurements at different spatial locations. Time-of-flight and Doppler broadening of the absorption with ∼0.1 Å spectral resolution indicate that the Na neutral vapor temperature is about 0.5–2 eV. Laser-induced fluorescence from ∼1×1012 cm−3 Na I 3s-3p lines observed with a streaked spectrograph provides a signal level sufficient for ∼±0.06 Å wavelength shift measurements in a mock-up of an ion diode experiment.
Optimal design of reflectometer density profile measurements using a radar systems approach (invited) (abstract)
Authors: Doyle E. J. , Kim K. W. , Peebles W. A. , Rhodes T. L.
Published: July 2002

Reflectometry is an attractive and versatile diagnostic technique that can address a wide range of measurement needs on fusion devices. However, progress in the area of profile measurement has been hampered by the lack of a well-understood basis for the optimum design and implementation of such systems. Such a design basis is provided by the realization that reflectometer systems utilized for density profile measurements are in fact specialized forms of radar systems. In this article five criteria are introduced by which reflectometer systems can be systematically designed for optimal performance: range resolution, spatial sampling, turbulence immunity, bandwidth optimization, and the need for adaptive data processing. Many of these criteria are familiar from radar systems analysis, and are applicable to reflectometry after allowance is made for differences stemming from the nature of the plasma target. These criteria are utilized to critically evaluate current reflectometer density profile techniques and indicate improvements that can impact current and next step devices, such as ITER.
A hammer-action micropositioner for scanning probe microscopes
Authors: Blackford B. L. , Jericho M. H.
Published: July 2002

The hammer-action effect produced by the closing of a miniature electromechanical relay was used to propel a rod along a track by the stick–slip inertial slider effect, with step sizes in the range of 30–500 nm and at frequencies up to 75 Hz. The rod was held tightly against the track by spring loaded balls so that the device worked well in any orientation, including vertical motion against gravity. The device was tested as the coarse approach mechanism in a scanning tunneling microscope, at room temperature and liquid nitrogen temperature. The voltage sensitivity actually increased as the temperature was lowered, which is a vast improvement over the piezoelectrically driven micropositioners previously reported in the literature. Further advantages over the piezotranslators are the simple square pulse driving voltage, the much reduced sensitivity to slider surface contaminations, and the improved rigidity. Motion in two- or three-dimensions would be possible by using two or three such translators mounted orthogonally.