bluuebunny/crossref_metadata_2025 huggingface dataset:
Tokamak Physics Experiment diagnostic plans (invited)
Authors: Medley S. S.
Published: July 2002

A superconducting Tokamak Physics Experiment (TPX) whose mission is to develop the scientific basis for a compact and continuously operating tokamak fusion reactor is being designed by an integrated U.S. national team. Key physics features such as strong shaping, a double-null poloidal divertor, full noninductive current drive, and current profile control capability will be used to explore improvements in energy confinement and beta limit scaling in high-aspect-ratio plasmas with a high bootstrap current fraction. Steady-state operation of TPX permits these studies to be extended to time scales significantly exceeding the global current-relaxation time and the plasma-wall equilibrium time. The diagnostic requirements are determined by the TPX mission and supporting objectives, such as optimization of plasma performance through active control of the current profile and of the plasma-wall interactions. Diagnostic measurements are needed to characterize the plasma behavior over the full range of conventional tokamak plasma parameters with appropriate spatial and temporal resolution as well as for control and monitoring of aspects of the machine operation such as the plasma position and shape, plasma current, vacuum vessel currents, electron density and temperature, and the divertor and limiter temperatures. In addition, several diagnostic capabilities that are especially critical for the TPX project will be discussed.
Miniature low-temperature high-frequency filters for single electronics
Authors: Courtois H. , Buisson O. , Chaussy J. , Pannetier B.
Published: July 2002

Single-electron devices are now very promising for high-accuracy and high-sensitivity electrical measurements, based on the quantification of the macroscopic charge in metallic nanostructures. The ultimate performance of these devices can only be attained by a careful filtering of the measurement circuit at very low temperature (20 mK). A new kind of wide-band high-frequency filter integrated on a copper block has been designed and studied. This original substrate provides a massive and well-thermalized electric ground plane in the vicinity of the filter. Attenuation measurements show that one has to carefully design the filter box in order to avoid the transmission of electromagnetic modes through the filter box. An improved filter showed −95 dB attenuation at 20 GHz, without any increase of the transmission at high frequency.
CO2 laser heating instrumentation at CHESSa)
Authors: Brister Keith , Bassett William
Published: July 2002

A new instrument constructed at the high-pressure facility at CHESS provides a simple mechanism to group MCA data on the basis of a rapidly varying sample temperature. This system allows powder diffraction from samples at simultaneous high pressures and high temperatures in a diamond-anvil cell. The instrument consists of a laser beam delivery system and incandescent light collection optics to analyze the resulting graybody spectra. A portion of the incandescent light controls into which multichannel analyzer group the x-ray-diffraction pattern accumulates. We illustrate the performance of the system with recent experiments.
Diagnosis of pusher-fuel mixing for high growth-factor implosions (abstract)a)
Authors: Landen O. L. , Hammel B. A. , Keane C. J. , Murphy T. J. , Hay R. G. , Lerche R. A. , Nelson M. B. , Cable M. D. , Kilkenny J. D. , Dittrich T. R. , Levedahl W. K. , Suter L. , Haan S. W. , Hatchett S. P. , McEachern R. , Cook R. , Wallace R. J.
Published: July 2002

The degradation in implosion performance of surface-pitted, indirectly driven Br-doped capsules which have been intentionally designed to be susceptible to large hydrodynamic instability growth has been systematically and reproducibly measured by a wide array of x-ray and neutron diagnostics. Primary and secondary neutron yields, and x-ray line ratios and durations from Ar and Ti fuel and pusher dopants are presented, showing clear sensitivity to increasing surface roughness and by inference, increasing pusher-fuel mix. The sensitivity of core x-ray emissivity and neutron bang-times to micron variations in capsule ablator thickness is also demonstrated. The experimental trends are compared to expectations based on two different models for the effects of instability growth at the pusher-fuel interface (atomic mixing versus Rayleigh–Taylor bubble-and-spike growth).
Ion-assisted pulsed-laser deposition
Authors: Reade R. P. , Church S. R. , Russo R. E.
Published: July 2002

Ion bombardment on the surface of a substrate during deposition of a thin film [ion-assisted (IA) deposition] is used to control thin-film crystalline orientation and phase. Ion-assisted deposition is demonstrated with the relatively new pulsed-laser deposition (PLD) technique, a method of thin-film growth that has shown promise for the synthesis of high-temperature superconductor and other complex oxide films. A versatile vacuum chamber with independent control of ion-gun parameters was developed for ion-assisted pulsed-laser deposition (IAPLD). Control of crystalline orientation and alignment of yttria-stabilized zirconia and CeO2 layers for use in YBa2Cu3O7−δ superconductor devices is demonstrated using this IAPLD technology.
A fiber-optics-based light scattering instrument for time-resolved simultaneous static and dynamic measurements
Authors: Egelhaaf S. U. , Schurtenberger P.
Published: July 2002

A fiber-optics-based multiangle light scattering instrument is presented, which permits time-resolved static and dynamic measurements. The scattered light is simultaneously collected at nine fixed directions using single and few mode fibers. Furthermore, a continuous range of scattering angles between 3.6° and 144.1° is obtained by changing the direction of the incident beam. The instrument is thus ideally suited for determinations of form and structure factors, which demand precise measurements over a large range of scattering angles, as well as for studies of aggregation phenomena or structural transitions, which require time-resolved multiangle measurements.
Status report on the electron cyclotron resonance ion sources used for the production of radioactive ion beams at Louvain-la-Neuve
Authors: Gaelens M. , Decrock P. , Huyse M. , Van Duppen P. , Loiselet M. , Ryckewaert G.
Published: July 2002

Two single-stage, 6 GHz electron cyclotron resonance (ECR) ion sources are currently in use at the ARENAS project at Louvain-la-Neuve. One of them is used to ionize radioactive elements to low charge states (1+ to 4+) before injection in the postaccelerator cyclotron. High intensity beams of 6He, 11C, 13N, 18Ne, and 19Ne are being produced. Recently the source has been adapted for the ionization of 18F and the first experiment with this beam has been performed. A second ECR source, almost identical to the first, is used in combination with the Leuven isotope separator on-line. It produces stable and radioactive beams at 50*q keV. Mass separated beams of 13N, 14O, and 15O can be produced using a high-temperature carbon target. An upgrade of this type of ECR source is now under construction. It consists mainly of increased magnetic fields and the capability for insertion of a heated cavity.
Construction of mini-ECRIS for the JAERI 400 kV ion implanter
Authors: Saitoh Y. , Yokota W.
Published: July 2002

A very compact 10 GHz ECRIS for production of medium-multiply charged ions was designed and manufactured in order to extend the beam energy from the 400 kV ion implanter at JAERI. To install the ion source at a high-voltage terminal where the available space and electric power feeding are limited, a magnetic field is formed only by permanent magnets (NdFeB), and a rf power up to 15 W is supplied by a transistor amplifier. The magnet measures 12 cm in length, and 3 cm and 11 cm in inner and outer diameter, respectively. The maximum mirror field is 5500 G and the total electric power consumption of the source is below 180 W. A beam current of 1.6 μA was observed for Ar4+ in test operations. The design and the results of the first operation at a test bench are reported.
An orthotropic source of thermal atoms
Authors: Dinneen Timothy , Ghiorso Albert , Gould Harvey
Published: July 2002

A source of thermal atoms that emits 100% of its atoms into a narrow beam with small angular divergence is described. It uses both surface ionization and surface neutralization in conjunction with electric fields to selectively emit a highly directional (orthotropic) beam of neutral atoms. The source can be modulated electronically and lends itself to scanning. This orthotropic source is ideal for the efficient use of rare atomic species, is well suited for atomic clocks, is essential for the efficient delivery of radioactive atoms to optical traps, and has the potential to produce ultrahigh intensity beams of stable atoms.
Method and a simple apparatus for rapid simultaneous measurement of resonance frequency and Q factor of a quartz crystal
Authors: Wajid Abdul
Published: July 2002

The quartz crystal microbalance is finding many novel uses beyond its traditional utility as a thin film deposition controller. In many situations where the quartz crystal is immersed in a viscous fluid, it is desirable to measure the crystal’s Q factor in addition to its resonance frequency. Here, we describe a simple method for simultaneous measurement of the resonance frequency, the quality factor, and the activity or relative amplitude of oscillation of a quartz crystal in vacuum and in gaseous environment. The hardware, comprising of a synthesized sine wave generator and a phase detector, passively interrogates the crystal to determine its resonance frequency and activity. The passive measurement system can detect a resonance even when the crystal is heavily damped. Representative measurement results for an AT-cut quartz crystal in a number of gases at various pressures are presented. The methodology described here may be readily applied to quartz crystals immersed in a liquid.
Technique for measuring magnetic filling factors with applications to cryogenic magnetic resonance experiments
Authors: Hayden M. E. , Hardy W. N.
Published: July 2002

We describe a new cavity perturbation technique for accurate measurement of rf magnetic filling factors, which is especially relevant to cryogenic magnetic resonance experiments. The sample volume is filled with liquid O2 which perturbs both the magnetic and electric rf fields within the electromagnetic resonator or cavity. The electric perturbation is subsequently accounted for by replacing the liquid O2 with liquid Ar which has nearly identical dielectric properties. The procedure may be refined using the dielectric properties of liquid N2 whereby the depolarizing factor associated with the sample volume may be estimated. In contrast to conventional techniques, the method usually requires little or no modification of the magnetic resonance apparatus. An ancillary result of our work has been the determination of the paramagnetic loss tangent for liquid oxygen near 80 K at 1.4 and 5.3 GHz.
Measurement of doubly differential electron distributions induced by atomic collisions: Apparatus and related instrumental effects
Authors: Bernardi G. , Suárez S. , Fregenal D. , Focke P. , Meckbach W.
Published: July 2002

We describe the experimental setup at Centro Atómico Bariloche for the measurement of doubly differential electron distributions, in energy and angle of emission, induced by atomic collisions. We present detailed information about the performance of the equipment including a discussion of instrumental effects that could have affected the measured spectra.
Phase sensitive detection of light reflected from a Fabry–Pérot interferometer
Authors: Bava E. , Massari F.
Published: July 2002

We present an analysis of the Fabry–Pérot response to a phase-modulated light in the reflection mode, by considering the general problem of the lock-in detection at the pth harmonics of the rf modulating frequency. Suitable frequency modulation conditions for servo-locking purposes are obtained and the values of modulation index which maximize the sensitivity for the first, third, and fifth harmonics are found. Moreover, we investigate the effects of the residual amplitude modulation introduced by the electro-optic frequency modulator, the presence of laser amplitude and frequency noise, and the dependence of the achievable closed-loop frequency fluctuation spectrum on the modulation index and detection noise.
Analytical correction of temperature in a logarithmic electrometer using light-emitting diodes
Authors: Acharya Y. B. , Aggarwal A. K.
Published: July 2002

The current–voltage characteristics of logarithmic amplifiers depend considerably on the ambient temperature. A theoretical correction has been estimated considering the temperature dependence of various parameters in the diode equation. A log electrometer using light-emitting diodes has been fabricated and its I–V characteristics are obtained experimentally for calibration and also to determine the device constant. If a measurement is obtained at a temperature other than the one for which calibration has been done, the theoretical correction can be applied to get the correct value. It has been shown that the theoretically corrected readings lie within ±4% of the experimentally obtained data in the temperature range of 5–60 °C for the operating current range of 10−12–10−4 A. The alternative can be to introduce temperature compensation circuitry into the logarithmic amplifier. However, this makes the electrometer circuit more complex. The proposed theoretical correction method may find applications where space and power are at a premium and the accuracy requirement is not very stringent.
A simple technique for the evaluation of a vertex using interference phenomena in the shadow region
Authors: Kanai N.
Published: July 2002

We have studied the dependence of the finish of the vertex of a wedge on the diffraction pattern experimentally. It is found that the three ray interference pattern in the shadow region of the samples arises from the rounded vertex of the wedge. The method reported in this article is shown to be a valuable technique to evaluate the finish of a vertex of a small wedge with an obtuse angle.
Combined ultrahigh vacuum scanning tunneling microscope scanning electron microscope system
Authors: Memmert U. , Hodel U. , Hartmann U.
Published: July 2002

We describe a combined ultrahigh vacuum scanning tunneling microscope (STM)–scanning electron microscope (SEM) system, which allows to position the STM tip with respect to the sample within an area of 5 mm×5 mm under SEM control. While the SEM resolution is sufficient to clearly resolve sub-μm structures on the samples, the STM features atomic resolution on semiconductor surfaces. The combination of SEM and STM allows high-resolution studies on inhomogeneous samples in materials research as well as the use for micro- and nanoelectronic device characterization or device modification. The STM performance was checked by atomically resolved imaging of Si(111) (7×7) surfaces. The STM/SEM combination and its application in device characterization is demonstrated by the investigation of vertically grown resonant tunneling diodes on an AlAs/GaAs basis. Due to its performance the system has a high potential for high-resolution imaging in materials research, for novel device characterization and nanoscale structuring or modification of very small devices.
Rate-scanning modified adiabatic calorimeter
Authors: Moon I. K. , Jeong Y. H.
Published: July 2002

We have developed a continuous cooling method, as a simple modification of adiabatic calorimetry which typically operates in the heating mode, with the capability of varying the scanning rate in the range of 0.01–2 K/min. This method allows us to determine the absolute value of specific heat of a liquid or solid during cooling as well as during heating in the temperature range between 100 and 400 K. The typical specific heat data of a supercooled liquid [Ca(NO3)2]0.4(KNO3)0.6 agree well with results by other methods.
Design studies on a vacuum bellows assembly with radio frequency shield for the KEK B factory
Authors: Suetsugu Y. , Ohshima K. , Kanazawa K.
Published: July 2002

A bellows assembly with a radio frequency (rf) shield has been designed and developed for the KEK B factory (KEKB). The rf shield is the usual finger type but has a special spring finger to press contact fingers onto the beam tube. A test of the mechanical performance using a trial model shows good results. Further experimental studies are focused on the two key points of the finger-type rf shield, that is, the contact force of fingers and the length of slits between adjacent fingers. First, to reduce the excess abrasion at contact points, the necessary contact force is studied experimentally utilizing microwaves. Abnormal heating is checked by transmitting a 508 MHz cw microwave through a trial model in a coaxial line. Arcing at the contact point in vacuum is observed by transmitting a 2856 MHz pulse microwave in a rectangular waveguide equipped with a model piece of the rf shield. A contact force of 50 g/finger is found to be necessary. Second, the optimum slit length is studied with a strategy to minimize the higher order mode (HOM) power leaked from the beam tube into the inside of the bellows while keeping a sufficient sliding stroke. The coupling coefficient, β, of the rf shield is measured experimentally from the Q value of a TE mode resonance in a cylindrical cavity connected to the bellows assembly. Using the measured dependence of β on the slit length, a rough estimation of leaked HOM power is tried for the KEKB. The expected leaked power is about 6–18 W for a slit length of 20 mm, which is in the allowable range. The results obtained through these experiments are reflected to the design for the KEKB: the contact force of 80–100 g/finger will be adopted finally considering the manufacturing error of typically ±10 g/finger in our test and leaving a margin for higher frequencies. The nominal slit length will be set to be 20 mm, keeping the expansion/contraction of ±10 mm.
Ion beam deceleration characteristics of a high-current, mass-separated, low-energy ion beam deposition system
Authors: Shimizu S. , Sasaki N. , Ogata S. , Tsukakoshi O.
Published: July 2002

Ion beam deceleration characteristics of a newly developed high-current, mass-separated, low-energy ion beam deposition system that utilizes an acceleration-deceleration method was studied. For realizing a high current ion beam of a mA level with energies down to 10 eV, the system developed is provided with a new ion beam deceleration system consisting of three cylindrical electrodes. Computer-simulated ion beam trajectory study indicates that ion beam convergence in the deceleration system required for suppressing the blowup of the ion beam due to the space charge effect depends on the electric potential distribution applied to these three electrodes. An Ar+ ion beam as high as 5.1 mA which is the highest ion current ever reported in the mass-separated, low-energy ion beam deposition system could be obtained at an ion energy of 100 eV under the optimum deceleration condition. Ion energy dependence of the Ar+ ion current at the target showing ion current decrease with the reduced ion energy was investigated utilizing a computer-simulated ion beam trajectory study.
Space-flight digital signal processor system for on-board processing of experiment data
Authors: Haas D. G. , Siefring C. L. , Baumback M. M. , Rodriguez P.
Published: July 2002

We have developed a digital signal processor (DSP) system to extend the capabilities of a variety of scientific instruments used to make in situ ionospheric plasma measurements from sounding rockets and spacecraft. The DSP system is extremely flexible due to the use of a field programmable gate array, sigma-delta analog-to-digital converters, and a highly integrated single-chip DSP. Using virtually identical circuitry, we have operated DSP systems processing data from low-frequency electric field detectors, Langmuir probes, and several radio-frequency receivers on several sounding rockets and spacecraft with different digital telemetry interfaces. The DSP system provides three major improvements to our instruments: (1) reduced telemetry bandwidth (data) requirements, (2) improved signal-to-noise ratio, and (3) digital antialiasing filtering. We describe our DSP system and show three examples of how we have implemented it with our instruments. Similar systems should be of interest to researchers in many fields of research.
A simple subnanosecond rise time test generator with variable pulse width and amplitudes up to 1 kV
Authors: Schuette A. , Rodrigo H.
Published: July 2002

A variable pulse length high voltage generator with rise times of 850 ps is described. The principle of operation of this generator is discussed. Also discussed are the uses of the generator and the limitations and ways of improving the fall time of the generated pulse. The main advantage of the generator presented here is its simplicity and low cost.
On the temporal resolution of multitau digital correlators
Authors: Phillies George D. J.
Published: July 2002

This article treats a class of systematic errors in determining the intensity–intensity correlation function S(t) with a digital correlator. Errors in determining S(t) will lead to incorrect computations of apparent diffusion coefficients and size distributions for micelles, vesicles, and other supramolecular assemblies. Systematic errors in interpreting the spectrum Sd(tm) measured by real correlators, in terms of the true spectrum S(t), are minimized by optimum interpretations of the delay time tm of each correlator channel. This identification is more complex for multitau correlators than for simple linear correlators. For a multitau correlator with current and delayed sampling times T and θ, and a delay channel beginning τ after the beginning of the zero-time sampling channel, the optimum choice is tm=τ−T/2+θ/2. The so-called ‘‘half-channel’’ correction tm=τ+θ/2 is erroneous. For the ‘‘zero delay channel’’ seen on some correlators, the most appropriate identification is tm=T/3.
High sensitivity image intensifier tube device for hard-x-ray detection
Authors: Dupuis V. , Cavailler C. , Noré D. , Jourdain M.
Published: July 2002

We present an x-ray detector with a high sensitivity in the 1–20 MeV x-ray range. This device consists of a scintillator coupled with a microchannel plate image intensifier tube working in the visible range. The performance of the hard-x-ray detector is described. The modulation transfer function, the characteristic curve, and the detection threshold were measured. Using an x-ray flash generator in the 4 MeV x-ray range, we have been able to record images of dense spheres for dose levels as low as 1.5 μGray. Similar experiments have been realized with a linear accelerator for different x-ray spectra (10 and 20 MeV). Our results demonstrate that this device works in a range where the most sensitive intensifying screens and films, usually used on flash radiography, are inoperative.
Low-energy Rutherford backscattering-ion channeling measurement system with the use of several tens keV hydrogen and a time-of-flight spectrometer
Authors: Hasegawa Masataka , Kobayashi Naoto , Hayashi Nobuyuki
Published: July 2002

We have developed a low-energy Rutherford backscattering spectrometry (RBS)-ion channeling measurement system for the analysis of thin films and solid surfaces with the use of several tens keV hydrogen ions and a time-of-flight spectrometer which was originally developed by Mendenhall and Weller. The depth resolution of our system is better than that of a conventional RBS system with MeV helium ions and silicon surface barrier detectors. This measurement system is very small in size compared to the conventional RBS-ion channeling measurement system with the use of MeV He ions, because of the small ion accelerator for several tens keV ions. The analysis of crystalline thin films which utilizes ion channeling effect can be performed with the use of this low-energy RBS-ion channeling measurement system. The in situ observation of the thermal reaction between iron and silicon substrate with the use of this measurement system is also demonstrated.
A high-voltage transmission-line pulse transformer with very low droop
Authors: Graneau P. N. , Rossi J. O. , Brown M. P. , Smith P. W.
Published: July 2002

The design, construction, and operational characteristics of a 200 kV transmission line pulse transformer is described. The transformer is wound using a new winding method that enhances the isolation of the output of the transformer from the input. As a result, pulse droop is substantially reduced, minimizing pulse distortion in the transformer. The ways in which both pulse rise time and droop can be further improved are investigated using a simple model for the transformer. The frequency response performance of the transformer is also described and modeled. As a result, it is shown that this type of transformer has the potential to be used as a high-frequency, continuously excited power transformer.
Low noise position sensitive detector for optical probe beam deflection measurements
Authors: Spear Jonathan D. , Russo Richard E.
Published: July 2002

We report the design of an optical position sensor that uses two discrete photodiodes electrically connected in parallel, with opposing polarities. A lens provides optical gain and restricts the acceptance angle of the detector. The response of the device to displacements of an optical spot is similar to that of a conventional bicell type position sensitive detector. However, the discrete photodiode design enables simpler electronic amplification with inherently less electrical noise than the bicell. Measurements by the sensor of the pointing noise of a focused helium–neon laser as a function of frequency demonstrate high sensitivity and suitability for optical probe beam deflection experiments.
Measurement of fast surface photovoltage relaxation
Authors: Hlávka J. , S̆vehla R.
Published: July 2002

A new version of the measuring circuit is presented which makes it possible to measure fast surface photovoltage relaxation in a simple way. An explanation of the experimental arrangement is given as well as illustrating the results.
A sapphire cell for neutron scattering at elevated pressures
Authors: Zielinski Richard G. , Paulaitis Michael E. , Kaler Eric W.
Published: July 2002

A pressure cell for cold neutron scattering from liquid solutions at elevated pressures is described. The scattering cell is constructed entirely of sapphire in order to transmit neutrons that scatter at angles as large as 29° while being optically transparent. The cell has been hydrostatically tested to 330 bar. In addition, it is surrounded by an aluminum jacket that permits heating and cooling of the sample to within ±0.05 °C of the setpoint from 25 to 35 °C, as measured by an in situ platinum RTD. This cell has been successfully used for scattering from surfactant/D2O/CO2 mixtures at pressures up to 90.7 bar.
A neutron camera for ITER (invited)
Authors: Marcus F. B. , Jarvis O. N. , Loughlin M. , Sadler G. , Stott P. , Adams J. M. , Bond D. S. , Hawkes N. P. , Watkins N. , Batistoni P. , Rapisarda M. , Elevant T. , Johnson L. , de Kock L. , Walker C.
Published: July 2002

Based upon JET experience, the measurement of multichannel collimated neutron fluxes and of the neutron spectrum gives time-dependent information on spatial profiles of neutron emission and alpha–particle birth, the total neutron emission (fuel burn-up rate), plasma position, effects of plasma instabilities, triton burn-up, ion temperature, and fuel densities. The design for a horizontally viewing neutron camera for ITER is based upon the prototype and upgrade versions of the JET neutron emission profile monitor and the JET spectrometers. It is proposed that vertically stacked modules are installed in the ITER biological shield in a fan shaped viewing geometry, aimed at a focal point located at the slit opening of a preshield designed to reduce the streaming neutron flux. Each module contains a pair of sight lines with adjustable collimation, allowing for multiple detector neutron flux monitoring and neutron spectroscopy over a wide operating range. The modular system allows flexibility in detector choice and viewing geometry.
Implosion symmetry and ρ
R
measurements on the National Ignition Facility from nascent 27–31 MeV tertiary protons (invited) (abstract)
Authors: Petrasso Richard D.
Published: July 2002

Tertiary protons with birth energies from ∼27 to 30.8 MeV result from the implosion of ignition-scale inertial confinement fusion targets, such as those planned for the National Ignition Facility (NIF). Measurement of the tertiaries’ slowing can provide a determination of the imploded areal density of the fuel capsule, as well as implosion asymmetry that results from anisotropy of the areal density and plasma temperature. In order to determine the utility of tertiaries for all phases of the NIF, we analyze three representative cases: a gas capsule (0.7 kJ yield); a cryogenic fuel capsule that fails to ignite (15 kJ); and a cryogenic fuel capsule that ignites and burns (13 000 kJ). In each case, tertiaries escape from the capsule and convey critical information about implosion dynamics. In addition, we show that for some gas-capsule implosions anticipated on OMEGA, tertiaries may be the only species of energetic charged particles that can determine the fuel areal density. Presently, we are building a charge-coupled device (CCD)-based charged particle spectrometer for OMEGA and for NOVA. In addition to the tertiaries, the spectrometers are sensitive to a variety of the energetic charged particles, such as knock-on protons, deuterons, and tritons, and He3-burnup protons. In fact the latter set of charged particles will usually be the dominant signal. We will describe the basic features of the spectrometers and the measured response of the CCDs to 1–5 MeV protons, 1–5 MeV alphas, and 14 MeV neutrons (and associated gammas), the latter constitute the principal source of noise. This work is done in collaboration with C. K. Li, D. Hicks, and F. Seguin of MIT; with B. Burke of LL/MIT; with M. Cable, S. Pollaine, S. Haan, T. Bernat, T. Phillips, and J. Kilkenny of LLNL; with J, Knauer, S. Cremer, C. Verdon, and B. Kremens of University of Rochester; and with C. Ruiz and R. Leeper of SNL. This work is supported in part by LLNL Subcontract B313875 and University of Rochester Subcontract 410025-G.
HPGe well-type detectors for neutron activation measurements on the Frascati Tokamak Upgrade tokamak
Authors: Bertalot L. , Damiani M. , Esposito B. , Lagamba L. , Podda S. , Batistoni P. , De Felice P. , Biagini R.
Published: July 2002

We describe an improvement of the neutron activation system in operation on the Frascati Tokamak Upgrade (FTU) tokamak for the measurement of the total neutron yield. A HPGe well-type detector (200 cm3 active volume) is used to detect the photoemission from neutron activated samples (115mIn 336.2 keV γ rays from DD neutrons on indium for FTU). Due to their high geometrical efficiency, HPGe well-type detectors are particularly suited to the FTU low-level activity measurements. A particular effort has been devoted to the calibration of the measuring system. In particular, a multi-γ calibration source (59–1332 keV energy range) with a density of 7.31 g/cm3 consisting of a stack of indium foils has been prepared. This assures that the shape and volume of the calibration source are the same as those of the samples used in the actual measurements. The full-energy-peak efficiency at the 115mIn 336.2 keV line is 0.197 with an overall uncertainty of 2% (1σ). For a better characterization of the detector response as a function of the sample density, a further calibration source with the same geometry has been prepared in a gel aqueous solution (density ∼1 g/cm3). The calibration curves for the well-type detector at the two different density values are compared.
Review of diagnostic methods for TFTR D–T radiation shielding and neutronics studies
Authors: Kugel H. W. , Ascione G. , Gilbert J. , Azziz N. , Goldhagen P. , Reginatto M. , Shebell P. , Kumar A.
Published: July 2002

The methods and instrument systems used for TFTR D–T radiation shielding and neutronics studies involving signal strengths ranging over 10 orders of magnitude are reviewed. Neutron and gamma dose-equivalent, fluence, spectral, and materials activation measurements have been performed at various locations from the TFTR vessel to the nearest property lines. The detection systems include 3He, BF3, and 235U proportional counters in moderated spheres, Bonner sphere arrays, advanced thermoluminescent detectors, argon ionization chambers, intrinsic Ge gamma detectors, and activation foil spectrometry methods.
Energy spectrum of thermonuclear neutrons
Authors: Ballabio L. , Gorini G. , Kallne J.
Published: July 2002

The neutron energy spectrum from d+t and d+d reactions in a thermonuclear fusion plasma is investigated with the help of a combination of analytical and numerical (Monte Carlo) methods. The energy moments of the neutron spectrum are analytically determined as a function of ion temperature (Ti) and the spectral shape is numerically determined over an intensity span of about 6 orders magnitude. The results are presented in the form of tables and interpolation formulas valid in the range 0<Ti<100 keV for use in the advanced diagnostic interpretation of potential high accuracy neutron spectrometry measurements on burning tokamak plasmas.
Neutron time-of-flight signals from expanding or contracting spherical sources
Authors: Murphy T. J. , Chrien R. E. , Klare K. A.
Published: July 2002

The width of the energy distribution of fusion-produced neutrons is often used as an indication of the temperature of the reacting ions. The Doppler broadening of the neutron energy is due to the center-of-mass velocity of reacting ion pairs and is characterized by the ion temperature for a Maxwellian distribution of ions with zero collective velocity. If there is bulk fluid motion or turbulence characterized by a velocity on the order of the ion thermal speed, a significant additional broadening may be introduced. Suggestions of this phenomenon have been observed for two classes of laser targets. The first is a “gas bag” target, in which a deuterated hydrocarbon gas is contained in a thin spherical membrane and illuminated uniformly. The second target is an ICF capsule with a deuterated plastic inner layer. In both cases, measured neutron energy distributions were wider than expected from theoretical ion temperatures and if interpreted as indicative of the ion temperature, are inconsistent with the neutron yields observed.
Proton recoil detector of fusion neutrons using natural diamond
Authors: Maqueda R. J. , Barnes Cris W. , Han S. S. , Staples P. A. , Wagner R. S.
Published: July 2002

Diamond, with its high radiation damage resistance, is an attractive alternative to silicon for neutron measurements in next step fusion experiments. A 200-μm-thick type IIa natural diamond with Ti/Au contacts was tested at the LAMPF-WNR facility by time-of-flight neutron energy identification. The crystal, having a carrier lifetime of up to 1 ns, was arranged in a low-energy-resolution, high-sensitivity proton recoil telescope consisting of a polyethylene radiator and a low-energy-proton Teflon filter. This arrangement is similar to the triton burnup monitor of Croft et al. [Rev. Sci. Instrum. 64, 1418 (1993)], where a silicon photodiode was used as a recoil proton detector. The observed sensitivity for 14 MeV neutrons (DT) is (1.25±0.15)×10−3 counts/neutron. However, a high contribution of neutron-induced events in the diamond, mainly carbon (A=12) recoils, was observed. A one-dimensional calculation for the detector response to carbon recoil and proton deposition is compared to the measurements. Poor energy resolution of the diamond detector precludes pulse height discrimination between direct 2.5 MeV neutrons events and proton events corresponding to 14 MeV neutrons. Therefore, an overall DT/DD neutron sensitivity ratio of only ∼6.5 is achieved. This value is much lower than the ratio of 540 reported by Croft et al. in their silicon (A=28) monitor.
The OMEGA laser electronic timing system
Authors: Kremens R. L. , Canosa J. T. , Brown D. , Hinterman T. , Letzring S. L. , Litchfield M. , Lonobile D. , Roides R. G. , Thomas M. , Weaver R.
Published: July 2002

A high-precision, computer-controlled electronic timing system has been built for the OMEGA inertial confinement fusion laser. The timing system consists of five modular subcomponents and is easily expandable to produce any number of delay channels. The timing from the system is synchronized by a distributed clock, which is derived from the radio-frequency-signal that drives the mode-locked laser master oscillator. The system produces IEEE RS-170 television synchronization signals and several subfrequencies for operating different parts of the laser. Performance of the system and cost will be discussed.
SODA: The reduced database for the TdeV tokamak
Authors: Côté A. , Michaud D. , Caumartin J. , de Villers P. , Gauthier Y. , Gauvreau J.-L. , Larsen J.-M.
Published: July 2002

SODA which stands for Système d’Organisation des Données et d’Analyse, is a general database for TdeV. SODA has the following goals: to produce a database of a reduced set of physical data; to ensure that these data are validated; to record all the parameters relevant to tokamak operation and experiments; to facilitate the retrieval of data using given selection criteria; and to improve data accessibility and analysis. The relational database ORACLE™ has been chosen to provide flexibility and to accommodate the increasing expectations of the TdeV researchers. In-house expertise allows custom-made tables and centralized data management. In the process of creating SODA several new interfaces for the scientific coordinator, machine operator, and diagnosticians have been added to provide a better definition of the experiment for the archiving system. The database includes the more relevant machine and diagnostic parameters, plasma perturbations (rf, biasing, gas…), mean and standard deviation of physical signals, plasma profiles, and code results (equilibrium…) for selected time windows in a discharge. Users of the X-window interface of SODA are not required to know the database structure or the SQL language. SODA has been operating successfully for over a year and its capabilities are continuously expanding.
New infrared thermal imaging camera diagnostic
Authors: Ciotti M. , Alessandrini C. , De Angelis A. , Vitale V. , Bernd S. , Maruccia G. , Greco V. , Molesini G.
Published: July 2002

The first-wall components of the next-generation machines will have to support very high thermal loads. Different solutions have been proposed to handle the energy flux in the scrape-off layer and to prevent the tiles from overheating. The necessity to monitor the tile surface temperature to prevent their damage has stimulated the development of reliable optical diagnostics, in spite of the severe constraints imposed by the hostile reactor environment. We have implemented a new infrared thermal imaging system on the Frascati Tokamak Upgrade machine. It has: (1) high dynamics to allow measurements in the whole temperature range covered during plasma operation; (2) high temporal resolution (<1 ms) for measurements during fast events as well as edge localized modes (ELMs) and disruptions; (3) high spatial resolution to discover hot spots, which can seriously affect plasma operations.
Measurements of edge density profiles on TdeV using the injection of laser-ablated lithium atoms
Authors: Abel G. , Stansfield B. , Michaud D. , Ross G. G. , Lachambre J. L. , Gauvreau J. L.
Published: July 2002

An atom injector using laser blow off of lithium is installed on TdeV to obtain the radial edge profile of electron density near the throat of the top divertor. The profile is reconstructed from the emissivity of the LiI (2p 2P→2s 2S) transition at 670.8 nm. A short review of the diagnostic is given describing the experimental setup, the measurement procedures, and the density profile reconstruction method. Effects of plasma biasing on the edge electron density profile and the response of the edge profile to the line-average central electron density are shown to illustrate the diagnostic capabilities.
Generation of 1 ns excimer laser output pulse by direct wave clipping
Authors: Shiqing Xiang , Qihong Lou , Jingxing Dong , Yanping Mang , Zhijiang Wang
Published: July 2002

In this article, a 1 ns excimer laser pulse was obtained successfully from an ultraviolet preionized XeCl laser using a direct wave-clipping technique with some improvements over the conventional scheme in consideration of obtaining more suitable discharge and steeper front edge of original light pulse. The effects of laser operation stability and optical setup of the experiment scheme on output characteristics are discussed.
Probing fe(v) by Thomson scattering on W7-X
Authors: Kühner G. , Knauer J. P. , Ringler H.
Published: July 2002

Thomson scattering is a widely used standard diagnostic for Te,ne measurements in fusion plasmas. Experience on W7-AS has shown, however, that during strong electron cyclotron resonance heating, the scattering spectra can be distorted by superthermal electrons. In addition, model calculations have shown that the distortion depends on the local magnetic field geometry. The Thomson diagnostic planned for W7-X provides for the first time, sufficient access to the vacuum vessel to probe several scattering geometries, allowing for scattering vectors parallel, perpendicular, and oblique with respect to the magnetic field. Furthermore, a detection system with high spectral resolution is foreseen so that there will be a good chance to reconstruct the two-dimensional electron distribution fe(v⊥,v∥).
Electron cyclon emission imaging of electron temperature profiles and fluctuations (invited)(abstract)
Authors: Cima G. , Deng B. , Domier C. W. , Geck W. R. , Hsia R. P. , Liang C. , Jiang F. , Luhmann, Jr. N. C. , Brower D. , Watts C.
Published: July 2002

Electron cyclotron emission (ECE) is a powerful diagnostic in a high performance/high magnetic field, magnetic confinement experiment, for a number of reasons. The most important one is probably due to the spatial localization of the ECE source, as opposed to most passive plasma diagnostics which perform line integrated measurements. The novel technique of ECE imaging, made possible by the existence of new arrays of high frequency mixers, fully exploits this property of ECE. A description of the device, an analysis of its characteristics, and a review of its preliminary results on TEXT-U will be given.
A two-dimensional regularization algorithm for density profile evaluation from broadband reflectometry
Authors: Nunes F. , Varela P. , Silva A. , Manso M. , Santos J. , Nunes I. , Serra F. , Kurzan B. , Suttrop W.
Published: July 2002

Broadband reflectometry is a current technique that uses the round-trip group delays of reflected frequency-swept waves to measure density profiles of fusion plasmas. The main factor that may limit the accuracy of the reconstructed profiles is the interference of the probing waves with the plasma density fluctuations: plasma turbulence leads to random phase variations and magneto hydrodynamic activity produces mainly strong amplitude and phase modulations. Both effects cause the decrease, and eventually loss, of signal at some frequencies. Several data processing techniques can be applied to filter and/or interpolate noisy group delay data obtained from turbulent plasmas with a single frequency sweep. Here, we propose a more powerful algorithm performing two-dimensional regularization (in space and time) of data provided by multiple consecutive frequency sweeps, which leads to density profiles with improved accuracy. The new method is described and its application to simulated data corrupted by noise and missing data is considered. It is shown that the algorithm improves the identification of slowly varying plasma density perturbations by attenuating the effect of fast fluctuations and noise contained in experimental data. First results obtained with this method in ASDEX Upgrade tokamak are presented.
Neural network tool for rapid recovery of plasma topology
Authors: Tribaldos V. , van Milligen B. Ph.
Published: July 2002

A general method for the rapid recovery of plasma topology based on a neural network fit of the normalized magnetic flux is presented. We propose a general method for coordinate inversions that is based on a neural network fit of the normalized magnetic flux. The neural network provides a flexible and compact base for representing the plasma topology and allows the evaluation of spatial derivatives by analytic methods (as opposed to finite-difference methods), making it faster than other techniques. We present examples of this technique for both two-dimensional plasmas (tokamak D shaped, X point) and stellarators.
Passive frequency and intensity stabilization of extended-cavity diode lasers
Authors: Talvitie H. , Pietiläinen A. , Ludvigsen H. , Ikonen E.
Published: July 2002

Studies are reported on frequency drifts in extended-cavity diode lasers caused by external effects, such as changes in temperature and air pressure. A laser system operating at 780 nm has been constructed utilizing low expansion materials and such mechanical structures that compensate for the external effects. By placing the laser system in a pressure-proof and temperature-controlled housing, a relative frequency stability of better than 10−10 (40 kHz) is obtained for integration times of 10 μs to 10 s. The drift of the laser frequency caused by spectral aging of the diode laser is about 3 MHz/h. As a consequence of high passive stability, the variations of the laser intensity are also greatly reduced to a relative drift value of 4×10−5/h.
Two-dimensional Cherenkov emission array for studies of relativistic electron dynamics in a laser plasma
Authors: Gordon D. , Lal A. , Wharton K. , Clayton C. E. , Joshi C.
Published: July 2002

In laser-produced plasmas there are several effects which will scatter a longitudinally probing relativistic electron beam. In vacuum, the laser itself will ponderomotively defocus the electron beam, while in plasma the ponderomotive force can dig an ion channel which would focus the electron beam. In the cases of plasma wave excitation via the beat-wave or wake-field mechanisms, the thermalization of the electron distribution function can lead to large scale magnetic fields via the Weibel instability. One way of studying such phenomena is to time resolve the transverse current distribution of the electron beam after it exits the plasma. A wire mesh has insufficient time resolution for this purpose, so we instead use a mesh of optical fibers. When the electron beam strikes the fiber mesh, Cherenkov radiation is generated within whichever fibers have current running across them. The Cherenkov radiation from all the fibers can then be analyzed on a streak camera. This allows the reconstruction of j(x,y,t) where j is the current density. We have successfully implemented this technique in the study of beat-excited laser plasmas.