bluuebunny/crossref_metadata_2025 huggingface dataset:
A neural networks framework for real-time unfolding of neutron spectroscopic data at JET
Authors: Ronchi E. , Conroy S. , Sundén E. A. , Ericsson G. , Hjalmarsson A. , Hellesen C. , Johnson M. G. , Weiszflog M. ,   JET-EFDA Contributors
Published: November 2008

A determination of fast ion population parameters such as intensity and kinetic temperature is important for fusion reactors. This becomes more challenging with finer time resolution of the measurements, since the limited data in each time slice cause increasing statistical variations in the data. This paper describes a framework using Bayesian-regularized neural networks (NNs) designed for such a task. The method is applied to the TOFOR 2.5MeV fusion neutron spectrometer at JET. NN training data are generated by random sampling of variables in neutron spectroscopy models. Ranges and probability distributions of the parameters are chosen to match the experimental data. Results have shown good performance both on synthetic and experimental data. The latter was assessed by statistical considerations and by examining the robustness and time consistency of the results. The regularization of the training algorithm allowed for higher time resolutions than simple forward methods. The fast execution time makes this approach suitable for real-time analysis with a time resolution limit in the microsecond time scale.
Design and initial operation of multichord soft x-ray detection arrays on the STOR-M tokamak
Authors: Xiao C. , Niu T. , Morelli J. E. , Paz-Soldan C. , Dreval M. , Elgriw S. , Pant A. , Rohraff D. , Trembach D. , Hirose A.
Published: November 2008

Two miniature pinhole camera arrays for spatially and temporally resolved measurements of soft x-ray emission have been designed and installed on the STOR-M tokamak. Each array consists of a photodiode array, with one array viewing vertically and one viewing horizontally through a plasma cross section. Preamplifiers with fixed gains of 105V∕A and custom built amplifiers with variable gains are used for signal amplification. Digitizers with 14bit resolution and 3MS∕s sampling rate are used for data acquisition. In the initial operation, an Al foil with a thickness of 1.8μm installed for one array and Be filter of 7.6μm installed for the other array are used to test signal strength. Initial tests have identified sawtooth oscillations and 20kHz fluctuations, which are also detected by Mirnov coils, superimposed on the sawtooth oscillations.
High resolution fast wave reflectometry: JET design and implications for ITER
Authors: Cupido L. , Cardinali A. , Igreja R. , Serra F. , Manso M. E. , Murari A. ,   JET-EFDA Contributors
Published: November 2008

The measurement of the fuel mixture remains a very difficult task in thermonuclear plasmas, where the hydrogen isotopes are fully stripped and do not emit line radiation. On the other hand, direct determination of the ion species mix will be essential in the reactor to keep the mixture close to 50∕50 and maximize the fusion output. In this paper, the design of fast wave reflectometry for JET is reviewed to show the potential of such a method in the perspective of ITER. The main design elements of the antenna and the detection system, based on vectorial measurements, are reported. The main challenges to such a diagnostic, mainly the intrinsic ion cyclotron emission from the plasma and the extensive use of ion cyclotron radiofrequencies as additional heating, are addressed in detail. The overall design indicates that the proposed system would be able to provide a measurement of the fuel ratio with spatial resolution in the range of few centimeters and temporal resolution in the range of 1ms in the vast majority of JET scenarios.
Magnetic diagnostics for the first plasma operation in Korea Superconducting Tokamak Advanced Research
Authors: Lee S. G. , Bak J. G. , Ka E. M. , Kim J. H. , Hahn S. H.
Published: November 2008

Magnetic diagnostics for the first plasma operation in the Korea Superconducting Tokamak Advanced Research device are described. The main discussion is the feasibility studies from the magnetic flux and field measurements utilizing the superconducting poloidal field coils before the first plasma generation.
The response of a radiation resistant ceramic scintillator (Al2O3:Cr) to low energy ions (–60keV)
Authors: Jimenez-Rey D. , Zurro B. , McCarthy K. J. , Garcia G. , Baciero A.
Published: November 2008

This work extends a previous study on ionoluminescence of a radiation-hard ceramic scintillator, Al2O3:Cr, to ions accelerated to keV energies [K. J. McCarthy et al., J. Nucl. Mater. 321, 78 (2003)]. It is motivated by the identification of this material as a promising candidate for use in the fast-ion-loss detector for ITER [for the range of thermal (low energy) and suprathermal ions]. In the paper we quantify and compare its ionoluminescence with that of some common luminescent materials (YAG:Ce and ruby) when irradiated by H+ ions accelerated to ⩽60keV using a purpose built laboratory setup. Next, studies are made on the ceramic to quantify its response as a function of incident ion mass, i.e., to He+. For this, the absolute luminosities of the material are estimated in terms of the number of photons emitted per incident ion as a function of energy. Moreover, the radiation hardness and postirradiation recovery of the ceramic are investigated. Finally, from the studies it can be concluded that the ceramic ruby is a good candidate for detecting low energy ions as long as its temporal response (approximately several milliseconds) is not a constraint for specific ion measurements.
An analysis of the influence of impurities on fast particle attenuation and on fast ion spectral shape in LHD
Authors: Veshchev Evgeny A. , Goncharov Pavel R. , Ozaki Tetsuo , Sudo Shigeru
Published: November 2008

Neutral particle fluxes measured by neutral particle analyzers can provide information about the ion temperature as well as the non-Maxwellian anisotropic ion distribution tails from neutral beam injection and ion cyclotron radio frequency heating. In the case of multidirectional diagnostics employing high resolution atomic energy spectrometers, the neutral atomic flux source is not localized in contrast to pellet charge exchange or diagnostic neutral beam methods. The correct interpretation of such measurements from plasma in a complex toroidally asymmetric geometry, like that of LHD, requires careful numerical modeling of the neutral flux formation. Previously a measured neutral flux calculation scheme was developed and was used for the LHD geometry and a suitable analytic expression for ionization cross sections σs(z)(E,ne,Te,Zeff) of impurities was formulated by Janev et al. [Nucl. Fusion 29, 2125 (1989)]. In this paper, the attenuation of fast particles by impurities is incorporated into the neutral flux calculation scheme and the influence of impurities on the calculated neutral flux spectra is shown. Finally, the behavior of the calculated and experimental suprathermal particle distributions is compared for pure hydrogen and for argon impurity seeded plasmas.
Energy resolved soft x-ray imaging using a charge coupled device camera for long pulse discharges in the Large Helical Device
Authors: Suzuki C. , Ida K. , Kobuchi T. , Yoshinuma M.
Published: November 2008

Energy resolved soft x-ray imaging system using a charge coupled device camera and a multifilter disk has recently been installed to the Large Helical Device for the measurements in the long pulse discharges. Eight images with different cutoff energies are measured sequentially during a single discharge by rotating a filter disk mounting eight beryllium filters with different thicknesses. A tangential line-integrated profile for a specific photon energy range can be obtained by taking intensity difference between two images measured with a filter pair of adjacent thicknesses. The typical photon energy corresponding to each difference ranges from 1.9to4.8keV with the bandwidth of 2–3keV. In the initial results, the difference in the line-integrated soft x-ray profile by the energy range has been clearly observed. This diagnostic method can possibly be applied to the observation of the dependence of two dimensional soft x-ray profile on photon energy range especially if local non-Maxwellian component appears in electron energy distribution function.
High performance compact magnetic spectrometers for energetic ion and electron measurement in ultraintense short pulse laser solid interactions
Authors: Chen Hui , Link Anthony J. , van Maren Roger , Patel Pravesh K. , Shepherd Ronnie , Wilks Scott C. , Beiersdorfer Peter
Published: November 2008

An ultraintense short pulse lasers incident on solid targets can generate relativistic electrons that then accelerate energetic protons and ions. These fast electrons and ions can effectively heat the solid target, beyond the region of direct laser interaction, and are important to realizing the fast ignition concept. To study these energetic ions and electrons produced from the laser-target interactions, we have developed a range of spectrometers that can cover a large energy range (from less than 0.1MeV to above 100MeV). They are physically compact, high performance, and low cost. We will present the basic design of these spectrometers and the test results from recent laser experiments.
Study of ITER plasma position reflectometer using a two-dimensional full-wave finite-difference time domain code
Authors: da Silva F. , Heuraux S.
Published: November 2008

The EU will supply the plasma position reflectometer for ITER. The system will have channels located at different poloidal positions, some of them obliquely viewing a plasma which has a poloidal density divergence and curvature, both adverse conditions for profile measurements. To understand the impact of such topology in the reconstruction of density profiles a full-wave two-dimensional finite-difference time domain O-mode code with the capability for frequency sweep was used. Simulations show that the reconstructed density profiles still meet the ITER radial accuracy specifications for plasma position (1cm), except for the highest densities. Other adverse effects such as multireflections induced by the blanket, density fluctuations, and MHD activity were considered and a first understanding on their impact obtained.
Fast ion measurement using a hybrid directional probe in the large helical device
Authors: Nagaoka Kenichi , Watanabe Kiyomasa Y. , Osakabe Masaki , Takeiri Yasuhiko , Minami Takashi , Toi Kazuo , Isobe Mitsutaka , Nishiura Masaki , Ito Takafumi , Ogawa Kunihiro
Published: November 2008

A hybrid directional probe was newly installed in the large helical device for fast ion measurement. The collector of the probe mounts a thermocouple to estimate local power flux and can be also utilized as a collector of a conventional Langmuir probe; therefore, the hybrid directional probe can simultaneously measure both local power density flux and current flux at the same collector surface. The concept and design of the hybrid directional probe, the calibration of the power density measurement, and preliminary result of the fast ion measurement are presented.
Charge exchange spectroscopy as a fast ion diagnostic on TEXTOR
Authors: Delabie E. , Jaspers R. J. E. , von Hellermann M. G. , Nielsen S. K. , Marchuk O.
Published: November 2008

An upgraded charge exchange spectroscopy diagnostic has been taken into operation at the TEXTOR tokamak. The angles of the viewing lines with the toroidal magnetic field are close to the pitch angles at birth of fast ions injected by one of the neutral beam injectors. Using another neutral beam for active spectroscopy, injected counter the direction in which fast ions injected by the first beam are circulating, we can simultaneously measure a fast ion tail on the blue wing of the Dα spectrum while the beam emission spectrum is Doppler shifted to the red wing. An analysis combining the two parts of the spectrum offers possibilities to improve the accuracy of the absolute (fast) ion density profiles. Fast beam modulation or passive viewing lines cannot be used for background subtraction on this diagnostic setup and therefore the background has to be modeled and fitted to the data together with a spectral model for the slowing down feature. The analysis of the fast ion Dα spectrum obtained with the new diagnostic is discussed.
Upgrade of the analyzer design for multipoint measurements by a gold neutral beam probe on the GAMMA 10 tandem mirror
Authors: Miyata Y. , Yoshikawa M. , Oono Y. , Mizuguchi M. , Nakashima Y. , Goshu S. , Nakada M. , Imai T.
Published: November 2008

The study of the mechanisms of both transport and fluctuations is one of the main issues of fusion plasma researches. Spatial fluctuation structure measurements are important for studying of cross correlation between the two fluctuations. Gold neutral beam probe systems are used in GAMMA 10 tandem mirror plasma device. Currently, the plasma potential and its fluctuations cannot be measured at different radial positions simultaneously. This paper presents the upgrade design of the 45° electrostatic energy analyzer for the simultaneous multipoint measurements of plasma parameters.
High contrast Kr gas jet Kα x-ray source for high energy density physics experiments
Authors: Kugland N. L. , Neumayer P. , Döppner T. , Chung H.-K. , Constantin C. G. , Girard F. , Glenzer S. H. , Kemp A. , Niemann C.
Published: November 2008

A high contrast 12.6keV Kr Kα source has been demonstrated on the petawatt-class Titan laser facility using strongly clustering Kr gas jet targets. The contrast ratio (Kα to continuum) is 65, with a competitive ultrashort pulse laser to x-ray conversion efficiency of 10−5. Filtered shadowgraphy indicates that the Kr Kα and Kβ x rays are emitted from a roughly 1×2mm2 emission volume, making this source suitable for area backlighting and scattering. Spectral calculations indicate a typical bulk electron temperature of 50–70eV (i.e., mean ionization state 13–16), based on the observed ratio of Kα to Kβ. Kr gas jets provide a debris-free high energy Kα source for time-resolved diagnosis of dense matter.
Overview of equilibrium reconstruction on DIII-D using new measurements from an expanded motional Stark effect diagnostic
Authors: Holcomb C. T. , Makowski M. A. , Allen S. L. , Meyer W. H. , Van Zeeland M. A.
Published: November 2008

Motional Stark effect (MSE) measurements constrain equilibrium reconstruction of DIII-D tokamak plasmas using the equilibrium code EFIT. In 2007, two new MSE arrays were brought online, bringing the system to three core arrays, two edge arrays, and 64 total channels. We present the first EFIT reconstructions using this expanded system. Safety factor and ER profiles produced by fitting to data from the two new arrays and one of the other three agree well with independent measurements. Comparison of the data from the three arrays that view the core shows that one of the older arrays is inconsistent with the other two unless the measured calibration factors for this array are adjusted. The required adjustments depend on the toroidal field and plasma current direction, and on still other uncertain factors that change as the plasma evolves. We discuss possible sources of calibration error for this array.
The radiation-tolerant x-ray monitor
Authors: Gott Yu. V. , Stepanenko M. M.
Published: November 2008

A vacuum photoelectric detector (monitor) (VPD) designed for plasma tomography, megnetohydrodynamics monitoring, and imaging with the help of thermal x-ray radiation on the ITER facility is described. Laboratory experiments demonstrate that VPD has high sensitivity to thermal x rays and low sensitivity to hard gamma rays and neutrons. The results of tests of a prototype of this monitor on a Co60 source of gamma rays, on nuclear reactor and its calibration using radiation from an x-ray tube, and tests of its serviceability on the T-10 facility are presented.
A proposed in-vessel calibration light source for the Joint European Torus
Authors: Biewer T. M. , Hillis D. L. , Stamp M. F. , Zastrow K.-D. ,   JET-EFDA Contributors
Published: November 2008

An in-vessel calibration light source (ICLS) is proposed for use during extended shutdown periods of the Joint European Torus (JET). The ICLS is primarily a 12in. integrating sphere (4in. opening) with four lamps (of known radiance), which can be positioned inside the JET vacuum vessel via the remote handling arm during interventions in the JET operating schedule. This will facilitate the in situ calibration of optical diagnostics, which rely on absolute light intensity measurements currently made when the diagnostics are removed from JET. The ICLS could ultimately reduce/remove the mechanical stresses associated with the repositioning of diagnostics for calibration purposes. At least 10 diagnostic systems (∼20 diagnostic subsystems) could benefit from the ICLS; in some instances the ICLS provides the only viable absolute-calibration strategy. Moreover, the ICLS will be a broad-spectrum white light source, enabling intensity calibrations at all visible wavelengths. A secondary benefit of the ICLS is in its use as an illumination source for making measurements of the reflectance (over a broad spectral range and at multiple angles) from the tiles lining the JET vacuum vessel. During the ITER-like wall intervention new Be, C, and W tiles will be installed in JET and their reflectance measured. Measurements made in subsequent JET interventions will provide data on the effect of high-temperature plasma operation on the reflectance of these tiles.
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laser polarimeter for Faraday rotation measurements in the DIII-D tokamak
Authors: Van Zeeland M. A. , Boivin R. L. , Carlstrom T. N. , Deterly T. M.
Published: November 2008

A tangential viewing, 10.59μm CO2 laser polarimeter for electron density measurements based on plasma induced Faraday rotation has been installed on DIII-D. The system uses colinear right- and left-hand circularly polarized beams with a difference frequency of 40MHz to generate the necessary signal for heterodyne phase detection. The high-resolution phase information required to adequately resolve degree level polarization rotation is obtained using an all-digital “real-time” phase demodulation scheme based on modern digital signal processing techniques. Initial application of the system to DIII-D disruption mitigation experiments utilizing “massive gas jet” injection exhibits reliable operation and excellent agreement with CO2 interferometer measurements; interestingly, the obtained Faraday rotation angles are in the range of those expected in ITER plasmas.
Intelligent technique to search for patterns within images in massive databases
Authors: Vega J. , Murari A. , Pereira A. , Portas A. , Castro P. ,   JET-EFDA Contributors
Published: November 2008

An image retrieval system for JET has been developed. The image database contains the images of the JET high speed visible camera. The system input is a pattern selected inside an image and the output is the group of frames (defined by their discharge numbers and time slices) that show patterns similar to the selected one. This approach is based on morphological pattern recognition and it should be emphasized that the pattern is found independently of its location in the frame. The technique encodes images into characters and, therefore, it transforms the pattern search into a character-matching problem.
Using a short-pulse diffraction-limited laser beam to probe filamentation of a random phase plate smoothed beam
Authors: Kline J. L. , Montgomery D. S. , Flippo K. A. , Johnson R. P. , Rose H. A. , Shimada T. , Williams E. A.
Published: November 2008

A short pulse (few picoseconds) laser probe provides high temporal resolution measurements to elucidate details of fast dynamic phenomena not observable with typical longer laser pulse probes and gated diagnostics. Such a short pulse laser probe (SPLP) has been used to measure filamentation of a random phase plate (RPP) smoothed laser beam in a gas-jet plasma. The plasma index of refraction due to driven density and temperature fluctuations by the RPP beam perturbs the phase front of a SPLP propagating at a 90° angle with respect to the RPP interaction beam. The density and temperature fluctuations are quasistatic on the time scale of the SPLP (∼2ps). The transmitted near-field intensity distribution from the SPLP provides a measure of the phase front perturbation. At low plasma densities, the transmitted intensity pattern is asymmetric with striations across the entire probe beam in the direction of the RPP smoothed beam. As the plasma density increases, the striations break up into smaller sizes along the direction of the RPP beam propagation. The breakup of the intensity pattern is consistent with self-focusing of the RPP smoothed interaction beam. Simulations of the experiment using the wave propagation code, PF3D, are in qualitative agreement demonstrating that the asymmetric striations can be attributed to the RPP driven density fluctuations. Quantification of the beam breakup measured by the transmitted SPLP could lead to a new method for measuring self-focusing of lasers in underdense plasmas.
Multipoint Thomson scattering diagnostic for the Madison Symmetric Torus reversed-field pinch
Authors: Reusch J. A. , Borchardt M. T. , Den Hartog D. J. , Falkowski A. F. , Holly D. J. , O’Connell R. , Stephens H. D.
Published: November 2008

The multipoint Thomson scattering diagnostic on the Madison Symmetric Torus (MST) is now fully operational with 21 spatial points, which cover the entire minor radius. Four full electron temperature profiles can be obtained during each MST discharge, with a variable delay between each profile. This system overcomes challenges that arise from the unique machine design, location, and plasma characteristics of MST. The machine design limits the maximum porthole diameter to 11.4cm, requiring a compact, re-entrant, seven element lens for scattered light collection. Limited space near MST necessitates a long beam path for the two Nd:YAG lasers requiring a remote beam line adjustment system to suppress drift in the beam position due to thermal expansion of the building. Due to the remote location of the laser head, substantial design effort was put into the creation of a set of safety interlocks for the laser system. The dynamic nature of MST plasmas and the wide range of operating space require a versatile scattered light detection system consisting of filter polychromators with temperature controlled avalanche photodiode detectors. We also implement an insertable integrating sphere, which travels along the laser beam path through the vacuum vessel, for the alignment of both the fiber optics and the lasers.
The NSTX fast-ion D-alpha diagnostic
Authors: Podestà M. , Heidbrink W. W. , Bell R. E. , Feder R.
Published: November 2008

A new diagnostic, aimed at energy-resolved measurements of the spatial and temporal dynamics of fast ions in NSTX plasmas, is described. It is based on active charge-exchange recombination spectroscopy. The fast-ion signal is inferred from light emitted in the wavelength range of the Dα line by fast ions recombining with an injected neutral beam. Two complementary systems are operational. The first system, based on a spectrometer coupled to a charge coupled device detector, has 16 channels with space, time, and energy resolution of 5cm, 10ms, and 10keV, respectively. The second system monitors the energy-integrated fast-ion signal on time scales of ∼20μs at three different radii. Signals are measured by a multianode photomultiplier tube. For both systems, each channel includes two paired views, intercepting and missing the neutral beam for a direct subtraction of the background signal not associated with fast ions. Examples of signals from the 2008 NSTX run are presented.
A three dimensional probe positioner
Authors: Intrator T. , Sun X. , Dorf L. , Furno I. , Lapenta G.
Published: November 2008

In order to sort out the physics that is important in many plasma experiments, data in three dimensions (3D) are becoming necessary. Access to the usual cylindrical vacuum vessel is typically restricted to radially or axially insertable probes that can pivot. The space that can be explored usually has significant restrictions either because probe travel must be along a travel path, or a “wobbly” probe positioner requires one to map between a moveable coordinate system and a preferred laboratory coordinate system. This could for example introduce errors in measurements of vector quantities such as magnetic field or flow. We describe the design and implementation of a 3D probe positioner that slides in two dimensions on a double O-ring seal and radially inserts along the third dimension. The net result is that a 3D space can be explored in a laboratory Cartesian reference frame.
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interframe time 2-frame 6.151keV x-ray imaging on the recently upgraded Z Accelerator: A progress report
Authors: Bennett G. R. , Smith I. C. , Shores J. E. , Sinars D. B. , Robertson G. , Atherton B. W. , Jones M. C. , Porter J. L.
Published: November 2008

When used for the production of an x-ray imaging backlighter source on Sandia National Laboratories’ recently upgraded 26MA Z Accelerator, the terawatt-class, multikilojoule, 526.57nm Z-Beamlet laser (ZBL) [P. K. Rambo et al., Appl. Opt. 44, 2421 (2005)], in conjunction with the 6.151keV (1s2-1s2p triplet line of He-like Mn) curved-crystal imager [D. B. Sinars et al., Rev. Sci. Instrum. 75, 3672 (2004); G. R. Bennett et al., Rev. Sci. Instrum. 77, 10E322 (2006)], is capable of providing a high quality x radiograph per Z shot for inertial confinement fusion (ICF), complex hydrodynamics, and other high-energy-density physics experiments. For example, this diagnostic has recently afforded microgram-scale mass perturbation measurements on an imploding ignition-scale 1mg ICF capsule [G. R. Bennett et al., Phys. Rev. Lett. 99, 205003 (2007)], where the perturbation was initiated by a surrogate deuterium-tritium (DT) fuel fill tube. Using an angle-time multiplexing technique, ZBL now has the capability to provide two spatially and temporally separated foci in the Z chamber, allowing “two-frame” imaging to be performed, with an interframe time range of 2–20ns. This multiplexing technique allows the full area of the four-pass amplifiers to be used for the two pulses, rather than split the amplifiers effectively into two rectangular sections, with one leg delayed with respect to the other, which would otherwise double the power imposed onto the various optics thereby halving the damage threshold, for the same irradiance on target. The 6.151keV two frame technique has recently been used to image imploding wire arrays, using a 7.3ns interframe time. The diagnostic will soon be converted to operate with p-rather than s-polarized laser light for enhanced laser absorption in the Mn foil, plus other changes (e.g., operation at the possibly brighter 6.181keV Mn 1s2-1s2p singlet line), to increase x-ray yields. Also, a highly sensitive inline multiframe ultrafast (1ns gate time) digital x-ray camera is being developed [G. R. Bennett et al., Rev. Sci. Instrum. 77, 10E322 (2006)] to extend the system to “four-frame” and markedly improve the signal-to-noise ratio. [At present, time-integrating Fuji BAS-TR2025 image plate (scanned with a Fuji BAS-5000 device) forms the time-integrated image-plane detector.]
Fringe jump analysis and electronic corrections for the Tore Supra far infrared interferometer
Authors: Gil C. , Barbuti A. , Elbèze D. , Pastor P. , Philip J. , Toulouse L.
Published: November 2008

On the Tore Supra tokamak, the ten-channel far infrared interferometer consists of a double color (119 and 195μm) system with two detectors for each channel to measure the plasma density. The phase measurement is obtained by combining a 100kHz shifted reference beam with the probing beam that has crossed the plasma. The achieved precision—a few percent of a fringe—is very good compared with the expected variations due to plasma, which are on the order of several fringes. However, the counting of the fringe variations can be affected when the signal is perturbed by electromagnetic interferences or when it deviates in the presence of strong plasma refraction changes occurring during ICRH breakdowns, pellet injections, or disruptions. This induces a strong decrease in the reliability of the measurement, which is an important concern when the diagnostic is used for density control. We describe in this paper the renewing of the electronics that has been achieved to reduce and correct the number of the so-called fringe jumps. A new zero crossing method for phase measurement is used, together with a field programable gate array semiconductor integration, to measure the phase and activate the algorithm of corrections every 10μs. Comparisons between a numerical oscilloscope analysis and the corrected acquired data in the case of laboratory amplitude modulation tests and in the case of real plasma perturbations are also discussed.
Real-time electron density measurements from Cotton–Mouton effect in JET machine
Authors: Brombin M. , Boboc A. , Zabeo L. , Murari A. ,   JET-EFDA Contributors
Published: November 2008

Real-time density profile measurements are essential for advanced fusion tokamak operation and interferometry is a proven method for this task. Nevertheless, as a consequence of edge localized modes, pellet injections, fast density increases, or disruptions, the interferometer is subject to fringe jumps, which produce loss of the signal preventing reliable use of the measured density in a real-time feedback controller. An alternative method to measure the density is polarimetry based on the Cotton–Mouton effect, which is proportional to the line-integrated electron density. A new analysis approach has been implemented and tested to verify the reliability of the Cotton–Mouton measurements for a wide range of plasma parameters and to compare the density evaluated from polarimetry with that from interferometry. The density measurements based on polarimetry are going to be integrated in the real-time control system of JET since the difference with the interferometry is within one fringe for more than 90% of the cases.
Optical transmission of glass for the National Ignition Facility near backscatter imagers under x-ray exposure
Authors: London R. A. , Froula D. H. , Sorce C. M. , Moody J. D. , Suter L. J. , Glenzer S. H. , Jones O. S. , Meezan N. B. , Rosen M. D.
Published: November 2008

In experiments at the National Ignition Facility (NIF), the near backscatter imager materials need to maintain high optical transmission while exposed to hohlraum generated x rays. Glass plates are incorporated in the design to protect the optical scattering plates from x-ray damage. Radiation environments spanning those expected on NIF have been produced at the Omega Laser Facility by symmetric laser illumination of 1mm sized gold spheres. The time-dependent ultraviolet transmission of sample glass plates was measured. The data are interpreted with a free electron absorption model. Combined with the simulations of the hohlraum x-ray emission, this model is used to predict the transmission of the glass plates on the NIF. We predict that the plates should perform adequately up to the peak of the laser pulse.
First measurements of the absolute neutron spectrum using the magnetic recoil spectrometer at OMEGA (invited)
Authors: Frenje J. A. , Casey D. T. , Li C. K. , Rygg J. R. , Séguin F. H. , Petrasso R. D. , Yu Glebov V. , Meyerhofer D. D. , Sangster T. C. , Hatchett S. , Haan S. , Cerjan C. , Landen O. , Moran M. , Song P. , Wilson D. C. , Leeper R. J.
Published: November 2008

A neutron spectrometer, called a magnetic recoil spectrometer (MRS), has been built and implemented at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] for absolute measurements of the neutron spectrum in the range of 6–30MeV, from which fuel areal density (ρR), ion temperature (Ti), and yield (Yn) can be determined. The results from the first MRS measurements of the absolute neutron spectrum are presented. In addition, measuring ρR at the National Ignition Facility (NIF) [G. H. Miller et al., Nucl. Fusion 44, S228 (2004)] will be essential for assessing implosion performance during all stages of development from surrogate implosions to cryogenic fizzles to ignited implosions. To accomplish this, we are also developing an MRS for the NIF. As much of the research and development and instrument optimization of the MRS at OMEGA are directly applicable to the MRS at the NIF, a description of the design and characterization of the MRS on the NIF is discussed as well.
Diamagnetic loop for the first plasma in the KSTAR machine
Authors: Bak J. G. , Lee S. G. , Ka E. M.
Published: November 2008

The diamagnetic loop (DL) is installed for the plasma diamagnetic measurement at the first plasma in the Korea superconducting tokamak advanced research (KSTAR) machine. Experimental results from the position measurement of the DL inside the KSTAR vacuum vessel and the vacuum flux measurement by using the DL for the evaluation of the geometrical data and the balance coefficient of the DL for the compensation of the vacuum flux in the diamagnetic measurement are described. In addition, a preliminary work of an instrument for a hardware compensation of the vacuum flux is presented.
Spectroscopic interferometer for coherence length spectroscopy of pulsed discharge plasma
Authors: Kim Yong W. , Poolyarat Nopporn
Published: November 2008

We have designed and constructed a spectroscopic interferometer, and test run its operation with a pulsed discharge plasma. The plasma is produced by capacitor discharge across a gap filled with neutral argon at selected pressures. Ablation of iron from the cathode adds to argon to form equilibrium plasma of an argon-iron mixture. The ablative mass addition is measured and incorporated into the system of Saha equations. The calculated plasma energy is compared to independently measured total energy injected into the plasma to determine the peak plasma temperature. The measured coherence length of an argon emission line shows a dependence on the direction of the line of sight and a scaling with collision time within the plasma.
Neutron spectrometer for ITER using silicon detectors
Authors: Conroy Sean W. , Weiszflog Matthias , Andersson-Sunden Erik , Ericsson Goran , Gatu-Johnson Maria , Hellesen Carl , Ronchi Emanuel , Sjostrand Henrik
Published: November 2008

High resolution neutron spectrometers provide information about plasma parameters at existing fusion experiments. Such a system may also be employed at ITER. Proton recoil telescopes have classically been used to detect neutrons with good energy resolution but poor efficiency. Using annular silicon detectors, it is possible to greatly increase the solid angle coverage and hence improve efficiency. Based on a simulation (MCNPX) study, the scaling of energy resolution, efficiency, and time to determine an ion temperature to 10% accuracy on foil thickness and detector location is shown. The latter quantity is used to determine the optimum foil thickness and detector geometry for specific plasma temperatures. For a 20keV deuterium-tritium (DT) plasma, 5.3% resolution with efficiency of 2.9×10−4ncm2 is attainable using the available detectors. This gives a temperature measurement with 10% accuracy in 1.1ms for a neutron flux of 2×109ncm−2. Multiple detectors can be used to further increase the efficiency if needed. A system of this kind could be tested in a future DT campaign at, for example, JET.
Real-time estimation of the poloidal wavenumber of ISTTOK tokamak magnetic fluctuations
Authors: Coelho R. , Alves D.
Published: November 2008

The successful control of a fusion plasma discharge relies on the continuous improvement of existing diagnostics and on the development of new ones based on innovative concepts. It is equally important to provide efficient numerical tools capable of extracting, in real time, the most important physical quantities emerging from the collected data. This encompasses, for instance, the determination of the wavenumber and amplitude tracking of plasma instabilities, a necessary ingredient for establishing in real time the type of feedback control stabilization scheme to be used. In this paper, the characterization of the wavenumber spectra of unstable modes observed in ISTTOK plasma discharges is addressed using a set of two poloidal arrays of magnetic coils (Mirnov coils). In particular, the prospect for the estimation of the poloidal wavenumber in real time using recursive filtering techniques is investigated. It is shown that, in contrast with typical cross-spectrum analysis, where a large dataset is required to estimate the wavenumbers, with this innovative technique, the wavenumber spectra may be obtained in faster time scales.
Gamma ray spectroscopy at high energy and high time resolution at JET
Authors: Tardocchi M. , Proverbio L. I. , Gorini G. , Grosso G. , Locatelli M. , Chugonov I. N. , Gin D. B. , Shevelev A. E. , Murari A. , Kiptily V. G. , Syme B. , Fernandes A. M. , Pereira R. C. , Sousa J. ,   JET-EFDA Contributors
Published: November 2008

In fusion plasmas gamma ray emission is caused by reactions of fast particles, such as fusion alpha particles, with impurities. Gamma ray spectroscopy at JET has provided valuable diagnostic information on fast fuel as well as fusion product ions. Improvements of these measurements are needed to fully exploit the flux increase provided by future high power experiments at JET and ITER. Limiting aspects are, for instance, the count rate capability due to a high neutron/gamma background combined with slow detector response and a modest energy resolution due to the low light yield of the scintillators. This paper describes the solutions developed for achieving higher energy resolution, signal to background, and time resolution. The detector design is described based on the new BrLa3 scintillator crystal. The paper will focus on hardware development, including a photomultiplier tube capable of stable operation at counting rate as high as 1MHz, the magnetic shielding, and the fast digital data acquisition system.
Calibration of a Thomson scattering diagnostic for fluctuation measurements
Authors: Stephens H. D. , Borchardt M. T. , Den Hartog D. J. , Falkowski A. F. , Holly D. J. , O’Connell R. , Reusch J. A.
Published: November 2008

Detailed calibrations of the Madison Symmetric Torus polychromator Thomson scattering system have been made suitable for electron temperature fluctuation measurements. All calibrations have taken place focusing on accuracy, ease of use and repeatability, and in situ measurements wherever possible. Novel calibration processes have been made possible with an insertable integrating sphere (ISIS), using an avalanche photodiode (APD) as a reference detector and optical parametric oscillator (OPO). Discussed are a novel in situ spatial calibration with the use of the ISIS, the use of an APD as a reference detector to streamline the APD calibration process, a standard dc spectral calibration, and in situ pulsed spectral calibration made possible with a combination of an OPO as a light source, the ISIS, and an APD used as a reference detector. In addition a relative quantum efficiency curve for the APDs is obtained to aid in uncertainty analysis.
Diagnostic developments for quasicontinuous operation of the Wendelstein 7-X stellarator
Authors: König R. , Cantarini J. , Dreier H. , Erckmann V. , Hildebrandt D. , Hirsch M. , Kocsis G. , Kornejew P. , Laux M. , Laqua H. , Pasch E. , Recsei S. , Szabó V. , Thomsen H. , Weller A. , Werner A. , Wolf R. , Ye M. Y. , Zoletnik S.
Published: November 2008

The stellarator Wendelstein 7-X will allow for quasicontinuous operation with the duration only being limited to two 30min discharges per day, at a continuous heating power of 10MW electron cyclotron resonance heating (ECRH) at 140GHz, by the capacity of the cooling water reservoir. This will result in high thermal loads on all plasma facing components of 50–100kW∕m2 from radiation alone and of up to about 500kW∕m2 on components additionally exposed to convective loads. In high density scenarios toroidally varying ECRH stray radiation levels of 50–200kW∕m2 need to be coped with, requiring careful material selection and different shielding and hardening techniques. Furthermore, a gradual buildup of coatings on plasma facing optical components, which without any measures being taken, would lead to high transmission losses already within a few days of long pulse operation (equivalent to about 1year of operation in pulsed devices like JET or ASDEX-upgrade) and therefore needs to be prevented as much as possible. In addition in situ cleaning as well as absolute calibration techniques need to be developed for all plasma facing optical systems. Here we report about some of our efforts to find, for various types of diagnostics, ways to cope with these adverse effects. Moreover, we give a few examples for individual diagnostic specific issues with respect to quasicontinuous operation, such as the development of a special integrator for the magnetic diagnostics as well as special interferometer types which can cope with unavoidable vibrations and slow path length changes due to, e.g., thermal expansion of the plasma vessel.
Duplex multiwire proportional x-ray detector for multichord time-resolved soft x-ray and electron temperature measurements on T-10 tokamak
Authors: Sushkov A. V. , Andreev V. F. , Kravtsov D. E.
Published: November 2008

Compact 64-channel multiwire proportional chamber is successfully used on T-10 and TCV tokamaks as a continuous-current soft x-ray detectors. The duplex multiwire proportional x-ray detector is a new generation of these detectors. It has been designed for simultaneous multichord measurement of plasma soft x-ray emissivity in a two spectral ranges and determination of the electron temperature by the two-absorber method. The detector consists of two identical multiwire proportional chambers filled by 90%Kr+10%CH4 gas mixture at atmospheric pressure. The first multiwire chamber has 64 channels. The second multiwire chamber (installed behind the first one) has 32 channels. Both chambers view the plasma through the one helium-filled slot-hole camera. Thus, the first multiwire chamber serves as an absorber filter for the second one. Such construction of the detector allows us in addition to soft x-ray measurements to provide measurement of the plasma core electron temperature with spatial resolution of about 2cm and a time resolution of less than 50μs. The construction of the detector and experimental results illustrating the potential of the diagnostic are presented.
Three-dimensional reconstruction of dust particle trajectories in the NSTX
Authors: Boeglin W. U. , Roquemore A. L. , Maqueda R.
Published: November 2008

Highly mobile incandescent dust particles are routinely observed on NSTX using two fast cameras operating in the visible region. An analysis method to reconstruct dust particle trajectories in space using two fast cameras is presented in this paper. Position accuracies of a few millimeters depending on the particle’s location have been achieved and particle velocities between 10 and 200m∕s have been observed.
Neutron emission spectroscopy results for internal transport barrier and mode conversion ion cyclotron resonance heating experiments at JET
Authors: Giacomelli L. , Hjalmarsson A. , Källne J. , Hellesen C. , Tardocchi M. , Gorini G. , Eester D. Van , Lerche E. , Johnson T. , Kiptily V. , Conroy S. , Sundén E. Andersson , Ericsson G. , Johnson M. Gatu , Sjöstrand H. , Weiszflog M. ,   JET-EFDA Contributors
Published: November 2008

The effect of ion cyclotron resonance heating (ICRH) on (H3e)D plasmas at JET was studied with the time of flight optimized rate (TOFOR) spectrometer dedicated to 2.5 MeV dd neutron measurements. In internal transport barrier (ITB) plasma experiments with large H3e concentrations (X(H3e)>15%) an increase in neutron yield was observed after the ITB disappeared but with the auxiliary neutral beam injection and ICRH power still applied. The analysis of the TOFOR data revealed the formation of a high energy (fast) D population in this regime. The results were compared to other mode conversion experiments with similar X(H3e) but slightly different heating conditions. In this study we report on the high energy neutron tails originating from the fast D ions and their correlation with X(H3e) and discuss the light it can shed on ICRH-plasma power coupling mechanisms.
Wide-angle point-to-point x-ray imaging with almost arbitrarily large angles of incidence
Authors: Bitter M. , Hill K. W. , Scott S. , Feder R. , Ko Jinseok , Ince-Cushman A. , Rice J. E.
Published: November 2008

The paper describes a new scheme for wide-angle point-to-point x-ray imaging with almost arbitrarily large angles of incidence by a matched pair of spherically bent crystals to eliminate the astigmatism, which is a well-known imaging error of spherical mirrors. In addition to x rays, the scheme should be applicable to a very broad spectrum of the electromagnetic radiation, including microwaves, infrared and visible light, as well as UV and extreme UV radiation, if the crystals are replaced with appropriate spherical reflectors. The scheme may also be applicable to the imaging with ultrasound.
Self-adaptive sampling rate data acquisition in JET’s correlation reflectometer
Authors: de Arcas G. , López J. M. , Ruiz M. , Barrera E. , Vega J. , Murari A. , Fonseca A. ,   JET-EFDA Contributors
Published: November 2008

Data acquisition systems with self-adaptive sampling rate capabilities have been proposed as a solution to reduce the shear amount of data collected in every discharge of present fusion devices. This paper discusses the design of such a system for its use in the KG8B correlation reflectometer at JET. The system, which is based on the ITMS platform, continuously adapts the sample rate during the acquisition depending on the signal bandwidth. Data are acquired continuously at the expected maximum sample rate and transferred to a memory buffer in the host processor. Thereafter the rest of the process is based on software. Data are read from the memory buffer in blocks and for each block an intelligent decimation algorithm is applied. The decimation algorithm determines the signal bandwidth for each block in order to choose the optimum sample rate for that block, and from there the decimation factor to be used. Memory buffers are used to adapt the throughput of the three main software modules (data acquisition, processing, and storage) following a typical producer-consumer architecture. The system optimizes the amount of data collected while maintaining the same information. Design issues are discussed and results of performance evaluation are presented.
High-energy, high-resolution x-ray imaging on the Trident short-pulse laser facility
Authors: Workman J. , Cobble J. , Flippo K. , Gautier D. C. , Letzring S.
Published: November 2008

With the completion of the Trident laser facility upgrade, 200TW high-energy laser pulses are now capable of producing x-ray pulses with energies in the range of 15–40keV, which will be used for high-spatial resolution radiography. A diagnostic suite is being developed on the laser system to investigate and characterize the x-ray emission from high-Z targets. This includes charge coupled device based single-photon counters, imaging plates, a high-energy electronic imager, spectral diagnostics, and optical and x-ray spot size diagnostics. We describe recent x-ray results from a commissioning campaign as well as describe the development and design of a high-energy spectrometer. X-ray radiographs taken at 22keV with a spatial resolution of 25μm are a first demonstration on this facility of high-energy, high-spatial resolution capability.