bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resolution ruby laser Thomson scattering diagnostic for the W7-AS stellarator
Authors: Knauer J. P. , Pasch E. , Kühner G. ,   the W7-AS Team
Published: March 2003

After reconstruction, the ruby Thomson scattering diagnostic for the W7-AS stellarator is now in operation to again cover the complete plasma cross section (420 mm), where the former photomultiplier-based polychromator system has been replaced by two individual Littrow-type polychromator setups (focal length 50 cm), using intensified charge coupled device cameras for light detection. A single-pulse ruby laser with high pulse energy is used as a light source. The light scattered by the plasma electrons is imaged upon a set of 45 fiber bundles. 30 bundles provide a high spatial resolution of 4 mm at the inner edge of the plasma. The remaining part of the view chord is observed with a spatial resolution of 20 mm. At the output, the fiber bundles form the entrance slits of the Littrow-type spectrometers. The spectral resolution of the edge spectrometer can be modified by exchanging the diffraction grating. Depending on the installed diffraction grating (600 or 1800 lines/mm) a total wavelength range of 80 nm (suitable for plasma edge investigations) or 320 nm (suitable for gradient investigations) can be surveyed. The spectral intensity and geometrical calibration of the presented diagnostic setup can be done in situ by means of a neon spectral lamp and a calibrated tungsten strip lamp. The absolute sensitivity calibration for the system is achieved using either Raman (at 723.8 nm) or Rayleigh (at laser wavelength) scattering as hydrogen gas filled up in the vacuum vessel (up to 100 mbar). Examples of electron density and temperature profiles measured under different plasma conditions are presented.
Two-dimensional correlation measurements of electron cyclotron emission fluctuations on the stellarator Wendelstein 7-AS
Authors: Bäumel S. , Michel G. , Hartfuß H. J. , Rodriguéz-Girones Arboli M. , Hartnagel H. L.
Published: March 2003

The miniaturization of receiver arrays permits the arrangement of numerous poloidally staggered radial sightlines of an electron cyclotron emission (ECE) diagnostic for the measurement of the electron temperature and its fluctuations, making two-dimensional (2D) imaging of the electron temperature and its fluctuations caused by plasma turbulence possible. For the stellarator W7-AS, the development of a fully monolithic microwave integrated circuit 150 GHz subharmonic mixer array is under development. As a first step, a 2D ECE system for the measurement of electron temperature fluctuations using four individual horn-reflector arrangements in conjunction with multichannel heterodyne radiometers was installed and set into operation. With Gaussian beam optics and four poloidally staggered sightlines, electron temperature fluctuations could be characterized in radial and poloidal directions simultaneously. First observations in purely electron cyclotron resonance heated stellarator plasmas reveal a broadband drift-wave feature. Earlier experiments showing a decrease of the electron temperature fluctuation level with increasing heating power were confirmed. Additionally, it was revealed, using the 2D ECE correlation radiometer, that an increased velocity shear might account for the decrease of the coherence length and thus for the reduction of the electron temperature fluctuation level.
Optimization of the FM-CW reflectometry W-band antenna for core density profile measurements on ASDEX Upgrade
Authors: Hacquin S. , Wagner D. , Manso M. , Borreicho J. , Farinha L.
Published: March 2003

A numerical study of the focused hog-horn antenna used for the W-band channel of the ASDEX Upgrade frequency modulated continuous wave reflectometry system is performed here. A mode matching code is used to accuretely model wave propagation in waveguide and antenna structures. Then the field distribution (amplitude and phase) in the horn aperture given by this code is used as an input for other codes computing wave propagation in the plasma. Evaluating the received energy in the antenna, we first analyze plasma effects as the nonalignment between the antenna and the plasma equatorial plane. We show in the case of an unfocused antenna that ray-tracing results are in qualitative agreement with full wave calculations. Simulations also confirm that hog-horn antennas allow improving the measurement performances in comparison with unfocused antennas. The role of location of the focusing point of a hog-horn antenna (depending on the antenna design) is then studied. It appears that the focusing point position should be optimized to maximize the energy received in the antenna. Finally, we show that a new design for the W-band antenna on the ASDEX Upgrade broadband reflectometry system could improve the performances of this diagnostic.
Design of a flexure for surface forces apparatus
Authors: Devaprakasam D. , Biswas S. K.
Published: March 2003

We report the design of a variation of a double cantilever flexure system used for the measurement of displacement and force in surface force apparatus (SFA). The new force sensor is called dual double cantilever. The simple cantilever flexure suffers rotation, sideways deflection, and thermal expansion at the free end when loaded normally and asymmetrically. In the double cantilever these errors are minimized to a second order. In the dual double cantilever flexure the stiffness is enhanced 16 times as that of a single cantilever flexure but the rotation, sideways deflection, and thermal expansion at the free end are brought to many orders below the instrument resolutions. The new design enables the measurement of deflection by optical and capacitive sensing methods. The stiffness and the strain of the aluminum alloy [AUG1(2024)] flexure were estimated [dimensions, length (l=50.5 mm), breadth (b=10.5 mm), and thickness (t=1.2 mm)] by finite element method and were also validated experimentally. The finite element method was also used to create a map for the selection of a flexure geometry relevant to the properties of material under investigation by a SFA or a nanoindenter.
Radial wave number spectrum of density fluctuations deduced from reflectometry phase signals
Authors: Heuraux S. , Hacquin S. , da Silva F. , Clairet F. , Sabot R. , Leclert G.
Published: March 2003

A method to extract the radial wave-number spectrum of the density fluctuations from the reflectometry phase signal is proposed and the main points to interpret it are described. The method buildup is based on reflectometry studies devoted to phase or amplitude variations induced by coherent density perturbations. These previous analyses show that all the wave numbers up to the Bragg detection limit kf (fluctuation radial wave number) <2ko (incident wave number in vacuum) contribute to the phase fluctuations. Although the main part comes from the vicinity of the cutoff layer the entire probing zone contributes to the phase fluctuations. The phase fluctuations dependencies in kf and L (length of the density gradient) found in the literature for the O mode have been estimated for the X mode in the Bragg backscattering zone in the case of extensive density perturbations. The assumptions used to establish this diagnostic and its limitations are discussed. The numerical study with a FDTD code in two-dimensional configuration including the reflectometer antenna shows that the contribution of the poloidal wave number can be neglected in the studied cases. The method used to recover the kf spectrum from the Tore Supra swept reflectometer data and the results are presented.
Applying the CO2 laser collective Thomson scattering results from JT-60U to other machines
Authors: Richards R. K. , Hutchinson D. P. , Bennett C. A. , Kondoh T. , Miura Y. , Lee S.
Published: March 2003

A collective Thomson scattering (CTS) system based on a pulsed CO2 laser is being developed to demonstrate the feasibility of alpha-particle diagnostics. Tests on this system are being conducted on the JT-60U tokamak. The system consists of a pulsed laser (15 J in 1:s at 10.6:m) and a wide band (∼8 GHz) heterodyne receiver with a quantum-well infrared photodetector [Liu et al., IEEE Electron Device Lett. 16, 253 (1995)]. Stray light is reduced by a notch filter containing hot CO2 gas. The heterodyne receiver is absolutely calibrated using a large area blackbody radiation source [Bennett et al., Appl. Opt. 27, 3324 (1988)]. Results from the tests on JT-60U indicate a larger than expected noise background, especially for the lower velocity measurements determined by the smaller frequency shifts from the laser line. These results are used to estimate the signal-to-noise ratio that would be expected for a CTS diagnostic installed on other devices; ITER (“the way” in Latin), Joint European Torus-Enhanced Performance JET-EP, and axially symmetric divertor experiment (ASDEX). Calculations and possible system improvements are presented.
Temporal evolution of temperature and density profiles of a laser compressed core (invited)
Authors: Ochi Y. , Golovkin I. , Mancini R. , Uschmann I. , Sunahara A. , Nishimura H. , Fujita K. , Louis S. , Nakai M. , Shiraga H. , Miyanaga N. , Azechi H. , Butzbach R. , Förster E. , Delettrez J. , Koch J. , Lee R. W. , Klein L.
Published: March 2003

Temporal evolutions of the electron temperature and density profiles in the inertial confinement fusion core plasma were obtained through a combination of experimental technology to create a uniform core, diagnostics developments, and a data analysis technique to obtain an optimal solution. In the experiment, time- and space-resolved x-ray spectroscopic measurements were carried out; an x-ray streak spectrograph and a monochromatic x-ray framing camera provided temporal evolution of x-ray spectrum and monochromatic emissivities, respectively. The spectrum and emissivity profile were iteratively fitted as a function of electron temperature, density, and space. Then, optimal solutions were successfully extracted with the help of Niched–Pareto genetic algorithm. Temporal behavior between those data is well corrected by comparing spatially and spectrally integrated intensities. The resultant profiles were compared with hydrocode simulations, showing that spatially averaged electron temperature and density evolutions are well replicated by the simulations, but their detail spatial profiles do not agree with them.
Proton imaging detection of transient electromagnetic fields in laser-plasma interactions (invited)
Authors: Borghesi M. , Schiavi A. , Campbell D. H. , Haines M. G. , Willi O. , Mackinnon A. J. , Patel P. , Galimberti M. , Gizzi L. A.
Published: March 2003

Due to their particular properties (small source size, low divergence, short duration, large number density), the beams of multi-MeV protons generated during the interaction of ultraintense (I>1019 W/cm2) short pulses with thin solid targets are most suited for use as a particle probe in laser–plasma experiments. In particular, the proton beams are a valuable diagnostic tool for the detection of electromagnetic fields. The recently developed proton imaging technique employs the beams, in a point-projection imaging scheme, as an easily synchronizable diagnostic tool in laser–plasma interactions, fields, with high temporal and spatial resolution. The broad energy spectrum of the beams coupled with an appropriate choice of detector (multiple layers of dosimetric film) allows temporal multiframe capability. By allowing, for the first time, diagnostic access to electric-field distributions in dense plasmas, this novel diagnostic opens up to investigation a whole new range of unexplored phenomena. Results obtained in experiments performed at the Rutherford Appleton Laboratory are discussed here. In particular, the article presents the measurement of highly transient electric fields related to the generation and dynamics of hot electron currents following ultraintense laser irradiation of targets. The experimental capabilities of the technique and the analysis procedure required are well exemplified by the data presented.
Energy-resolved neutron imaging for inertial confinement fusion
Authors: Moran M. J. , Haan S. W. , Hatchett S. P. , Izumi N. , Koch J. A. , Lerche R. A. , Phillips T. W.
Published: March 2003

The success of the National Ignition Facility program will depend on diagnostic measurements which study the performance of inertial confinement fusion (ICF) experiments. Neutron yield, fusion-burn time history, and images are examples of important diagnostics. Neutron and x-ray images will record the geometries of compressed targets during the fusion-burn process. Such images provide a critical test of the accuracy of numerical modeling of ICF experiments. They also can provide valuable information in cases where experiments produce unexpected results. Although x-ray and neutron images provide similar data, they do have significant differences. X-ray images represent the distribution of high-temperature regions where fusion occurs, while neutron images directly reveal the spatial distribution of fusion-neutron emission. X-ray imaging has the advantage of a relatively straightforward path to the imaging system design. Neutron imaging, by using energy-resolved detection, offers the intriguing advantage of being able to provide independent images of burning and nonburning regions of the nuclear fuel. The usefulness of energy-resolved neutron imaging depends on both the information content of the data and on the quality of the data that can be recorded. The information content will relate to the characteristic neutron spectra that are associated with emission from different regions of the source. Numerical modeling of ICF fusion burn will be required to interpret the corresponding energy-dependent images. The exercise will be useful only if the images can be recorded with sufficient definition to reveal the spatial and energy-dependent features of interest. Several options are being evaluated with respect to the feasibility of providing the desired simultaneous spatial and energy resolution.
Goals for and design of a neutron pinhole imaging system for ignition capsules
Authors: Wilson D. C. , Christensen C. R. , Morgan G. L. , Wilke M. D. , Bradley P. A. , Gobby P. L.
Published: March 2003

Neutron yield at the National Ignition Facility (NIF) or the Laser MegaJoule (LMJ) will range from 1019 for a capsule that ignites and burns well to below 1015 for one that fails to ignite. Expected image sizes in deuterium–tritium (DT) neutrons decrease with the neutron yield. At 1018–1019 yields the capsules have ignited and are burning main fuel, producing images with full width at half maximum (FWHM) of ∼100 μm which require a 200 μm field of view and would need 10 μm resolution. Marginally igniting capsules, with yields of 1017 to 1018, burn the hot spot and some main fuel. Their neutron images are smaller, ∼60 μm FWHM, and require ∼120 μm field of view, with 7 μm resolution needed. Below ∼1017, the capsule fails to ignite and a field of view of ∼100 μm suffices to image the hot spot which might be ∼30 μm FWHM with a resolution of ∼5 μm. Images in downscattered neutrons are as large or larger than the time integrated images, have ∼5% of the brightness, and require correspondingly larger fields of view and are useful at lower resolution. A neutron imaging system can be designed to meet these requirements. One design for a neutron aperture is symmetric, biconic, with no clear opening. The opening angle of the cone defines the aperture’s effective area, point spread function, and hence the resolution. The field of view is determined by the cone angle and the distance from the capsule, and hence is coupled to the aperture resolution. Detector resolution determines the required magnification and thereby the minimum capsule to detector distance. At NIF a 20 cm long tungsten aperture with its front face 15 cm from the capsule could produce images with 5 μm resolution at yields down to 1016 in directions normal to the indirect drive Hohlraum axis. Image noise levels could be comparable to those already achieved on the Omega laser. Imaging in downscattered DT neutrons, typically 9.4–13 MeV and several percent in number compared to the DT neutrons, requires a detector with relatively fast decay time to recover after the arrival of the 14 MeV neutrons. The larger, fainter images reflecting the cold, main DT fuel, which demand less resolution, might be imaged through a second aperture with larger effective area located in the same pinhole assembly. In addition to a line of sight normal to the Hohlraum axis, a second line of sight along the axis is needed to diagnose nonaxisymmetric asymmetries.
Neutron images recorded with high-resolution bubble detectors
Authors: Lerche R. A. , Izumi N. , Fisher R. K. , Disdier L. , Bourgade J.-L. , Rouyer A. , Jaanimagi P. A. , Sangster T. C.
Published: March 2003

Neutron images have been successfully recorded with “gel-type bubble detectors.” 14 MeV fusion neutrons emitted from laser-irradiated inertial confinement fusion targets formed coded images in proof-of-principle experiments conducted at the OMEGA laser facility. In the detector, small (∼50 μm diameter) bubbles form when high-energy neutrons collide with the detector material. Each collision produces only one bubble whose position can be determined with a precision of better than 25 μm. Additionally, bubble detectors are insensitive to x-ray and gamma-ray background. For these ride-along experiments, bubble detectors were simply inserted between the imaging aperture and the scintillation detector of the primary experiment. Recorded images for high-yield (6×1013) targets show the bubble detector’s potential for high resolution. More complex “liquid” bubble detectors are expected to have efficiencies of ∼1% (versus 0.001% for gel-type) while maintaining the desirable characteristics of the gel-type units. This article discusses the bubble detector, the characteristics that make them an attractive recording device for neutron imaging, and initial bubble detector images. Simulation of the image statistics and the potential impact of bubble detectors on image system design are also discussed.
Ten-inch manipulator-based neutron temporal diagnostic for cryogenic experiments on OMEGA
Authors: Stoeckl C. , Glebov V. Yu. , Roberts S. , Sangster T. C. , Lerche R. A. , Griffith R. L. , Sorce C.
Published: March 2003

Measurements of the neutron emission from inertial confinement fusion implosions provide important information about target performance that can be compared directly with numerical models. For room-temperature target experiments on OMEGA at the Laboratory for Laser Energetics (LLE) the neutron temporal diagnostic (NTD), originally developed at Lawrence Livermore National Laboratory, is used to measure the neutron burn history with high resolution and good timing accuracy. The NTD is mechanically incompatible with cryogenic target experiments because of the standoff required to remain clear of the cryogenic target handling system, A cryogenic-compatible neutron temporal diagnostic (cryoNTD) has been designed for LLE’s standard ten-inch manipulator diagnostic inserters. This instrument provides high-resolution neutron emission measurements for cryogenic implosions. Experimental results of the performance of cryoNTD compared to NTD on room-temperature direct-drive implosions and on cryogenic implosions are presented.
Development of a gated scintillation fiber neutron detector for areal density measurements of inertial confinement fusion capsules
Authors: Izumi N. , Lerche R. A. , Phillips T. W. , Schmid G. J. , Moran M. J. , Koch J. A. , Azechi H. , Sangster T. C.
Published: March 2003

A detector for fuel areal density measurements in inertial confinement fusion capsules has been designed. Observation of neutrons scattered in an imploded deuterium capsule (0.27–0.6 MeV) is a promising method for areal density measurements in the National Ignition Facility DD surrogate capsules. In order to detect scattered neutrons, we need to (1) suppress interference due to the strong direct neutron burst and (2) suppress the background produced by neutrons scattering on nontarget material (mainly from the target chamber). In our detector system, we suppress direct neutrons by gating the detector. We suppress the nontarget background neutrons by placing the detector outside the target chamber and limiting the view of the detector with collimators. In addition, we are developing a lithium-glass scintillation-fiber detector (LG-SCIFI) to detect the scattered neutrons. The LG-SCIFI will work as a multichannel scintillator array. The scintillation signal will be amplified by a microchannel plate image intensifier, which is gated to accept signals only in a specific time-of-flight window for the scattered neutrons. The gated scintillation image will be recorded by a charge-coupled device. Since the detector is segmented, neutron detection events will be clearly identified as bright spots in the gated image.
Development of in-vessel neutron monitor using micro-fission chambers for ITER
Authors: Yamauchi M. , Nishitani T. , Ochiai K. , Morimoto Y. , Hori J. , Ebisawa K. , Kasai S. , Walker C.
Published: March 2003

A neutron monitor using micro-fission chambers to be installed inside the vacuum vessel has been designed for the International Thermonuclear Experimental Reactor (ITER). The monitoring system needs to be insensitive to the changes of the plasma position and the profile, and the locations behind upper and lower outboard blankets were selected as appropriate based on the neutron transport calculations with the Monte Carlo code for neutron and photon transport (MCNP). Employing both pulse counting and Campbelling modes in the electronics, the ITER requirement of 107 dynamic range with 1 ms temporal resolution will be accomplished. The system meets the 10% accuracy required for the fusion power monitor. A set of a U235 micro-fission chamber with 12 mg UO2 and a fissile-material-free “blank” detector to eliminate noise issues arising from γ rays, etc. were fabricated based on the design. The vacuum leak rate of the chamber with the mineral insulated (MI) cable, resistances between the central conductor and outer sheath, and mechanical strength up to 50 G acceleration were tested to meet the design criteria. The output signals for γ rays were measured with the Co60 γ-ray irradiation facility at Japan Atomic Energy Research Institute (JAERI)-Takasaki and the influence was estimated to be less than 0.1% of the signals for neutrons. Excellent linearities between count rates, square of Campbelling voltage, and neutron fluxes were confirmed in the temperature range from 20 °C (room) to 250 °C with the Fusion Neutronics Source (FNS) facility of JAERI. The influence of the surrounding material was studied with the shielding blanket mock-up, and it was verified that the chamber provides an effective response although the sensitivity was enhanced by slow-downed neutrons. As a result, it was concluded that the present micro-fission chamber is applicable to ITER power monitoring.
Neutron activation system using water flow for ITER
Authors: Nishitani T. , Ebisawa K. , Kasai S. , Walker C.
Published: March 2003

A neutron activation system with flowing water using the O16(n,p)16N reaction has been designed for the International Thermonuclear Experimental Reaction (ITER) neutron yield monitor with temporal resolution, based on the experimental results carried out at the fusion neutronics source (FNS) facility of the Japan Atomic Energy Research Institute. On ITER, irradiation ends will be installed in the filler shielding module between the blanket modules at the equatorial ports. The gamma-ray counting stations will be installed on the upstairs of the pit outside the biological shield. BGO (Bi4Ge3O12) scintillation detectors will be employed to measure 6.13 MeV gamma rays emitted from N16. The distance between the irradiation end and the counting station is ∼20 m. The performance of the neutron activation system has been evaluated by using the neutron Monte Carlo code MCNP-4b with the JENDL 3.2 library. The reaction rate of O16(n,p)16N was calculated not only at the irradiation end but also along the transfer line, which showed that the temporal resolution would be less than the ITER requirement of 100 ms including turbulent diffusion effects for the flow velocity of 10 m/s. With a flow velocity of 10 m/s, this system can measure the fusion power from 50 kW to 1 GW of the ITER operation by using two gamma-ray detectors; one detector faces the water pipe directly, and another has a collimator for higher-neutron yield. Also the calculation shows that the reaction rate is relatively insensitive to the change of the plasma position.
Conceptual design of beam-ion profile diagnostics for the DIII-D tokamak
Authors: Heidbrink W. W. , Cross W. D. , Krasilnikov A. V.
Published: March 2003

Three diagnostic concepts that measure the radial profile of deuterium beam ions are assessed. One diagnostic exploits 3 MeV protons that are lost on their first orbit. Since beam-plasma reactions usually predominate in the discharges of interest, the beam-ion density profile can be inferred from the d-d fusion reaction profile. The relatively modest plasma current (∼1.6 MA) implies that a significant fraction of the charged d-d fusion reaction products are unconfined. The second diagnostic employs a neutron collimator. For this diagnostic, neutron scattering is a major concern. Both fusion product diagnostics are sensitive to uncertainties in the thermonuclear rate, so the anomalous beam-ion transport must exceed DB≳1.0 m2/s to be detectable. The third diagnostic employs an array of natural diamond detectors that is configured to measure the signal from beam ions that charge exchange with neutrals in a modulated heating beam. The sensitivity to uncertainties caused by pitch-angle scattering of the beam ions can be minimized by a prudent choice of detection angle. Because of attenuation of the escaping neutrals the effective resolution is DB∼0.5 m2/s.
Thin foil Faraday collectors as a radiation hard fast lost-ion diagnostic
Authors: Cecil F. E. , Aakhus-Witt A. , Hawbaker J. , Sayers J. , Bozek A. , Heidbrink W. W. , Darrow D. S. , Debey T. M. , Marmar E.
Published: March 2003

We are investigating thin foil Faraday collectors as a diagnostic for lost fast ions from tokamak fusion plasmas. Prototype devices have been recently installed in the National Spherical Torus Experiment and DIII-D. Initial results from these devices indicate a loss of energetic ions from a variety of plasma conditions. Results from a device installed immediately outside a thin Be window on ALCATOR C-mod, as a test on the response to moderately intense fluxes of soft x rays indicate an upper limit of about 2×10−22 A/photon/cm2 at a plasma electron temperature of 1.8 keV. An important property of the diagnostic is the expected ability to operate under fairly high neutron/gamma radiation backgrounds. We have tested this expectation by measuring the current from a thin (2.5 μm) Ni foil placed in the core of a TRIGA fission reactor. At a maximum steady-state power of 950 kW (1013 n/cm2/s), a current of 1.2 nA/cm2 was measured.
The TOFOR spectrometer for 2.5 MeV neutron measurements at JET
Authors: Hjalmarsson A. , Conroy S. , Ericsson G. , Giacomelli L. , Gorini G. , Henriksson H. , Källne J. , Tardocchi M. , Weiszflog M.
Published: March 2003

Neutron emission spectroscopy has been demonstrated to be a powerful plasma diagnostic at tokamaks. This was shown with the magnetic proton recoil spectrometer developed for measurement of the 14 MeV neutron emission from deuterium–tritium (DT) plasmas at the Joint European Torus (JET). For diagnosis of D plasmas, a 2.5 MeV spectrometer is needed with a factor of 100 higher efficiency to maintain the count rate because of the lower neutron emission rate. The time-of-flight (TOF) technique has the right attributes for these measurements. However, previous instruments have not achieved the full potential of the technique, especially, with respect to count rate capability. A TOF spectrometer for optimized rate (TOFOR) has been conceptually defined and is now under design and development for construction and use at JET. The TOFOR design goal is a count rate capability of about 300 kHz which should be attainable in high power D discharges at JET. The TOFOR project is now in a research and development stage where the instrument is being characterized through neutron transport calculations and test experiments. The tests aim to determine the response of the plastic scintillator elements from which TOFOR will be constructed. This contribution will present the TOFOR design principles, the results of the simulations and test measurements, and the steps taken to reach the optimized design.
Calibration experiments of He3 neutron detectors for analyzing neutron emissivity in the hot-ion mode on the GAMMA 10 tandem mirror
Authors: Kohagura J. , Cho T. , Hirata M. , Watanabe H. , Minami R. , Numakura T. , Yoshida M. , Ito H. , Tatematsu Y. , Yatsu K. , Miyoshi S. , Ogura K. , Kondoh T. , Nishitani T. , Kwon M. , England A. C.
Published: March 2003

Under the international fusion cooperating research, He3 neutron detectors in the GAMMA 10 tandem mirror are calibrated by the use of a Cf252 spontaneous fission neutron source (8.96×104 n/s). The calibration experiments are carried out with a “rail system” placed along the magnetic axis of the GAMMA 10 central-cell region, where hot ions in the plasma experiments with the bulk temperatures of ∼10 keV are produced. As compared to a previous neutron monitoring system with a BF3 detector in GAMMA 10, the present He3 systems are designed with about two orders-of-magnitude higher neutron-counting efficiency for analyzing a neutron emissivity from the plasmas in a single plasma discharge alone. Two He3 systems are installed near the middle and the end of the central cell so as to identify the central-cell hot-ion axial profile. The filling pressure of He3, the effective length, and the diameter of the detector are designed as 5 bar, 300 mm, and 50 mm, respectively. The detector output spectra are carefully analyzed by the use of a preamplifier, a shaping amplifier, as well as a multichannel analyzer for each He3 detector. In the present article, the neutron-counting data from the two He3 detectors due to the on-axis Cf252 scan are interpreted in terms of the d−2 intensity dependence (d being the distance between the detector and the neutron source) as well as the effects of the central-cell magnetic coils and the other machine structural components.
Diagnostics and steady-state high power operation
Authors: Laviron Clément ,   and the Tore Supra Team
Published: March 2003

TORE SUPRA has now been upgraded to handle high power plasmas for very long duration. It came back into operation in 2001, and the goals are to extend the performances, in power and in duration, to be expressed in terms of energy. The design is such that a plasma discharge of 25 MW during 1000 s could be sustained, with actively cooled components in a steady-state condition. This corresponds to 25 GJ, orders of magnitude above other existing tokamaks and relevant to ITER conditions. The importance of diagnostics for missions other than physics understanding increases, such as machine operation or safety control. All TORE SUPRA diagnostics have been revisited to take into account these new constraints. Only a few of them did not need to be modified, most had to be adapted, upgraded, or even completely rebuilt. The main constraint deals with the thermal load on diagnostic components, the need to optimize the geometry and develop specific protections often with active cooling. The specific developments now implemented and operational on TORE SUPRA will be presented. Another requirement concerns the need for more control loops in order to maintain optimized modes of plasma operation for very long periods. Diagnostics are operated in real time, with the ability to transmit any kind of pertinent information on a fast time scale. This requires strict procedures, higher reliability, and stability of calibration of the relevant diagnostics. In addition, data can be accessed in real time, without waiting for the end of the pulse.
Diagnostics for FIRE: A status report
Authors: Young Kenneth M.
Published: March 2003

The mission for the proposed fusion ignition research experiment (FIRE) device is to “attain, explore, understand and optimize fusion-dominated plasmas.” Operation at Q⩾5, for 20 s with a fusion power output of ∼150 MW is the major goal. Attaining this mission sets demands for plasma measurement which are at least as comprehensive as on present tokamaks, with the additional capabilities needed for control of the plasma and for understanding the effects of the alpha-particles. Because of the planned operation in advanced tokamak scenarios, with steep transport barriers, the diagnostic instrumentation must be able to provide fine spatial and temporal resolution. It must also be able to withstand the impact of the intense neutron and gamma irradiation. There are practical engineering issues of minimizing radiation streaming while providing essential diagnostic access to the plasma. Many components will operate close to the first wall, e.g., ceramics and mineral insulated cable for magnetic diagnostics and mirrors for optical diagnostics; these components must be selected and mounted so that they will operate and survive in fluxes which require special material selection. The measurement requirements have been assessed so that the diagnostics for the FIRE device can be defined. Clearly, a better set of diagnostics of alpha-particles than that available for TFTR is essential, since the alpha-particles provide the dominant sources of heating and of instability-drive in the plasma.
Data acquisition and analysis system for the TPE-RX reversed-field pinch
Authors: Koguchi H. , Yagi Y. , Hirano Y. , Shimada T. , Sakakita H. , Sekine S.
Published: March 2003

Data acquisition and analysis systems for a reversed-field pinch (RFP) machine, the toroidal pinch experiment (RX) [TPE-RX, R/a=1.72/0.45 m, Ip<1 MA (designed)], are presented. Many kinds of diagnostic systems are installed on TPE-RX, and 392 signal channels at maximum from the diagnostic systems are routinely acquired by using the Computer Automated Measurement and Control system. The data are acquired through a serial highway into a front-end computer. A custom made, special computer program system, called DAQR, has been developed for the data acquisition routine. Software libraries are also developed for the data analyses of the plasma parameters, perturbed mode structures of the RFP plasma, and radiation from plasma.
Real-time analysis of charge-exchange spectroscopy data at JET
Authors: Heesterman P. J. L. , Sall I. , Giraud C. , Zastrow K-D. , Meigs A. , Felton R. , Joffrin E.
Published: March 2003

An algorithm has been implemented at Joint European Torus (JET) for real-time analysis of data from the charge-exchange diagnostic. TI and rotation data are produced and can be used in control feedback experiments. The algorithm used has been validated by comparison with previous off-line analysis.
X-ray induced fluorescence measurement of density distributions in a metal–halide lighting arc
Authors: Curry J. J. , Adler H. G. , Shastri S. D. , Lee W.-K.
Published: March 2003

The use of x-ray induced fluorescence to measure elemental densities in a metal–halide lighting arc is described. High-energy synchrotron radiation generated on the Sector 1 Insertion Device beam line at the Advanced Photon Source induces K-shell fluorescence in a high-pressure plasma arc. The detected fluorescence is spectrally resolved, so that multiple elemental species are observed simultaneously. Absolute calibration of the measured densities is straightforward and robust. The penetrating nature of high-energy photons allows these measurements to be made in situ, with the arc contained by an optically translucent polycrystalline alumina (Al2O3) arc tube and a glass vacuum jacket. Spatial distributions extending from one end of the arc tube to the other and from the arc core all the way to the wall have been obtained for all the principal elements in the arc. A volume element measuring 1 mm × 1 mm × 1 mm is resolved in the present work, with significantly better spatial resolution possible. Densities as low as 2×1016 cm−3 have been observed. X-ray induced fluorescence is useful for the observation of many important high-pressure plasma lighting chemistries including those containing Hg, Tl, Dy, Tm, Ho, Cs, Sn, I, and Xe.
Hypervelocity dust beam injection for internal magnetic field mapping
Authors: Wang Zhehui , Wurden G. A.
Published: March 2003

Injecting neutral atoms into high-temperature plasmas forms the basis for several important diagnostics, such as motional Stark effect and charge exchange recombination spectroscopy. We describe an alternative approach to seeding the plasma with neutrals, via “hypervelocity dust beam injection” (HDBI), using micron-sized dusts. Among its many potential applications, HDBI mapping of two-dimensional internal magnetic fields inside medium-sized (50–500 eV) plasmas is discussed in detail. Electrostatic acceleration at ∼100–200 kV will launch a stream of (0.2–10 μm-sized) dust grains of lithium or carbon to hypervelocities (1–10 km/s). Each dust grain, acting as a “microcomet” in the plasma, forming a plume (tail), which if photographed, will reveal the direction of the local magnetic field, with anywhere from 10–100 microcomets in the plasma at any time, a full profile of the B-field direction could be obtained per high resolution image. Due to the small dust grain size, the perturbation to the plasma will be minimal. HDBI could be a simple low cost approach to obtain internal magnetic field information in plasmas with magnetic field structures that are significantly different than vacuum fields, such as in spherical tokamaks, FRC's, RFP's, and spheromaks.
Initial neutral particle analyzer measurements of ion temperature in the National Spherical Torus Experiment
Authors: Medley S. S. , Bell R. E. , Petrov M. P. , Roquemore A. L. , Suvorkin E. V.
Published: March 2003

The neutral particle analyzer (NPA) diagnostic on the National Spherical Torus Experiment (NSTX) utilizes a PPPL-designed E∥B spectrometer which measures the energy spectra of minority H and bulk D species simultaneously with 39 energy channels per mass species and a time resolution of 1 ms. The calibrated energy range is E=0.5–150 keV and the energy resolution varies from ΔE/E=3%–7% over the surface of the microchannel plate detector. The NPA measures thermal Maxwellian ion spectra to obtain line integrated ion temperatures, Ti. For line integral electron densities below neL∼3.5×1019 m−2, good agreement is observed between the line integrated NPA Ti and the central Ti(0) measured by the spatially localized charge exchange recombination spectroscopy (CHERS) diagnostic. However, with increasingly higher neL the NPA Ti falls below the central Ti(0) measured by CHERS because the charge exchange neutral emissivity weights the line integrated NPA measurement outboard of the plasma core. An analytic neutral analysis code, DOUBLE, has been applied to the NPA data to correct for this effect and restore agreement with Ti(0) measured by CHERS. A description of the NPA diagnostic on NSTX and initial ion temperature measurements along with an illustration of application of the DOUBLE code are presented.
Fast neutral pressure measurements in NSTX
Authors: Raman R. , Kugel H. W. , Provost T. , Gernhardt R. , Jarboe T. R. , Bell M. G.
Published: March 2003

Several fast neutral pressure gauges have been installed on the National Spherical Torus Experiment (NSTX) to measure the vessel and divertor pressure during inductive and coaxial helicity injected plasma operations. Modified, Princeton divertor experiment-type Penning gauges have been installed on the upper and lower divertors. Neutral pressure measurements during plasma operations from these and from two shielded fast microion gauges at different toroidal locations on the vessel midplane are described. A new unshielded ion gauge, referred to as the in-vessel neutral pressure gauge is under development.
Observations of differences in the spatial-profile symmetry-of ion-confining potentials in the cases with and without the central-cell density increase during an ion-plugging period
Authors: Yoshida M. , Cho T. , Hirata M. , Ito H. , Kohagura J. , Yatsu K. , Miyoshi S.
Published: March 2003

Temporal evolution of radial profiles of end-loss-ion currents, ion temperatures, and ion-confining potentials φc is investigated in the GAMMA 10 tandem mirror by the use of our newly designed electrostatic ion-energy-spectrometer arrays. In tandem-mirror experiments, plasma-confining potentials produced by electron-cyclotron heatings (ECH’s) play one of the most critical roles in the improvement of simple-mirror plasma confinement. For the observations of these confining potentials, the development of ion-diagnostics equipment providing clear energy spectra without disturbances from ECH produced energetic electrons is of essential importance, since conventional multigrided Faraday cup signals are seriously influenced by such incident electrons. Each spectrometer unit in our developed array has a specific structure with obliquely placed multiple grids with respect to the direction of the ambient lines of magnetic force for plasma confinement. The relation between the spatial profiles of end-loss-ion fluxes IELA and those of φc is investigated by the use of these newly designed ion-energy-spectrometer arrays installed in both end regions of GAMMA 10. The first remarkable finding of axisymmetric profiles of φc having a good correlation with axisymmetric plugging distributions in IELA along with the central-cell density nc increase is made; while, the contrary result without nc increase even during a plugging period is found with asymmetric profiles of φc with asymmetric plugging profiles in IELA. In the article, detailed data comparison between the two is reported by the use of each single-plasma discharge with the developed ion-spectrometer arrays.
A novel electrostatic ion-energy spectrometer by the use of a proposed “self-collection” method for secondary-electron emission from a metal collector
Authors: Hirata M. , Nagashima S. , Cho T. , Kohagura J. , Yoshida M. , Ito H. , Numakura T. , Minami R. , Kondoh T. , Nakashima Y. , Yatsu K. , Miyoshi S.
Published: March 2003

For the purpose of end-loss-ion energy analyses in open-field plasmas, a newly developed electrostatic ion-energy spectrometer is proposed on the basis of a “self-collection” principle for secondary-electron emission from a metal collector. The ion-energy spectrometer is designed with multiple grids for analyzing incident ion energies, and a set of parallelly placed metal plates with respect to lines of ambient magnetic forces in an open-ended device. One of the most important characteristic properties of this spectrometer is the use of our proposed principle of a “self-collection” mechanism due to E×B drifts for secondary electrons emitted from the grounded metal-plate collector by the use of no further additional magnetic systems except the ambient open-ended fields B. The proof-of-principle and characterization experiments are carried out by the use of a test-ion-beam line along with an additional use of a Helmholtz coil system for the formation of open magnetic fields similar to those in the GAMMA 10 end region. The applications of the developed ion-energy spectrometer for end-loss-ion diagnostics in the GAMMA 10 plasma experiments are demonstrated under the conditions with simultaneous incidence of energetic electrons produced by electron-cyclotron heatings for end-loss-plugging potential formation, since these electrons have contributed to disturb these ion signals from conventional end-loss-ion detectors.
CVD diamond as a high bandwidth neutron detector for inertial confinement fusion diagnostics
Authors: Schmid G. J. , Griffith R. L. , Izumi N. , Koch J. A. , Lerche R. A. , Moran M. J. , Phillips T. W. , Turner R. E. , Glebov V. Yu. , Sangster T. C. , Stoeckl C.
Published: March 2003

We characterize the response of chemical vapor deposition (CVD) diamond detectors to inertial confinement fusion (ICF) neutrons generated at the OMEGA laser fusion facility in Rochester, NY. Four detectors are tested: three utilizing “optical grade” CVD diamond, and one utilizing “electronic grade” CVD diamond. Using a 50 Ω measurement system, we find that the optical grade wafers, biased to 1000 V/mm, have an average sensitivity of 0.24 μV ns/n for 2.5 MeV (DD fusion) neutrons and 0.62 μV ns/n for 14.0 MeV (DT fusion) neutrons. At the same E field, the electronic grade wafer has a sensitivity of 0.56 and 1.43 μV ns/n for 2.5 and 14 MeV neutrons, respectively. Linear dynamic range for the optical grade material is shown to be at least 105. Average full width at half maximum response times, as measured with pulsed laser and 3 GHz scope, are 376 and 880 ps for optical and electronic grades, respectively. These characteristics make CVD diamond suitable for ICF applications such as neutron time-of-flight spectroscopy, bang time measurements, and ion temperature measurements.
First observation of Moiré fringes in a proton beam generated by a 100 fs laser pulse
Authors: Mackinnon A. J. , Patel P. K. , Price D. W. , Hicks D. , Borghesi M. , Romagnani L.
Published: March 2003

High contrast Moiré fringes have been observed when two gratings were inserted into a proton beam produced from the interaction of a 100 TW laser beam with a thin solid foil. Moiré fringes with modulation close to 20% were observed in protons with energies between 4 and 7 MeV. The fringes were rotated with respect to a collimated optical test beam, a finding consistent with the protons originating from a point source close to the original target surface. These important results indicate that proton Moiré can be used as a high precision diagnostic of proton beam deflections from electric and magnetic fields in plasmas.
Thin foil calorimeter calibration using a 2 MV Van de Graaff accelerator
Authors: Freeman C. G. , Burke D. R. , Erhardt R. J. , DeCiantis J. L. , Padalino S. J. , Knauer J. P.
Published: March 2003

The Laboratory for Laser Energetics at the University of Rochester uses a set of thin foil calorimeters to study the absorbed energy in direct-drive inertial confinement fusion. Each calorimeter consists of two tantalum foils and a copper reference plate of equivalent thermal mass. The foils are approximately 25 μm thick and have a frontal area of approximately 1 cm2. A set of type-E thermocouples is used to make three differential temperature measurements (foil 1-reference, foil 2-reference, and foil 1-foil 2). We have developed a technique to calibrate the response of these thin foil calorimeters “off-line” using proton beams of 800 keV from the 2 MV Van de Graaff accelerator located at the Geneseo Nuclear Structure Laboratory. The calibration constants obtained for 16 calorimeter foils are clustered within ±10% of 7 mV/J. The uncertainty in each measurement is typically less than 5%.
Diagnosing the velocity-space separatrix of trapped particle modes
Authors: Kabantsev A. A. , Driscoll C. F.
Published: March 2003

Trapped particle modes in pure electron plasmas are similar to modes in neutral plasmas and exhibit damping due to velocity diffusion across the separatrix between trapped and untrapped particles, as commonly occurs in neutral plasmas. Applied rf voltages cause resonant perturbation of particle velocities near the separatrix, giving a greatly enhanced mode damping. This diagnostic technique can determine the velocity-space separatrices for either electrostatic or magnetic trapping, or determine the particle distribution function along the separatrix.