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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Fringe jump analysis and implementation of polarimetry on the ASDEX Upgrade DCN interferometer

The ASDEX Upgrade tokamak is equipped with a 5-channel DCN interferometer with a probing wavelength of 195 μm. Up to now, phase measurement and density calculation have been accomplished by hard-wired phase counting electronics. Meanwhile, a fast digitizer has been installed which acquires the raw signals. That way, the various causes of counting errors by integer multiples of 2π, so-called fringe jumps, can be analyzed, and phase reconstruction schemes based on digital signal processing can be developed. In addition, a prototype polarimeter setup has been installed on one channel and allows for measurement of the Faraday rotation experienced by the probing beam.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Resolving the bulk ion region of millimeter-wave collective Thomson scattering spectra at ASDEX Upgrade

Collective Thomson scattering (CTS) measurements provide information about the composition and velocity distribution of confined ion populations in fusion plasmas. The bulk ion part of the CTS spectrum is dominated by scattering off fluctuations driven by the motion of thermalized ion populations. It thus contains information about the ion temperature, rotation velocity, and plasma composition. To resolve the bulk ion region and access this information, we installed a fast acquisition system capable of sampling rates up to 12.5 GS/s in the CTS system at ASDEX Upgrade. CTS spectra with frequency resolution in the range of 1 MHz are then obtained through direct digitization and Fourier analysis of the CTS signal. We here describe the design, calibration, and operation of the fast receiver system and give examples of measured bulk ion CTS spectra showing the effects of changing ion temperature, rotation velocity, and plasma composition.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Neutron resonance spin-echo upgrade at the three-axis spectrometer FLEXX

We describe the upgrade of the neutron resonance spin-echo setup at the cold neutron triple-axis spectrometer FLEXX at the BER II neutron source at the Helmholtz-Zentrum Berlin. The parameters of redesigned key components are discussed, including the radio frequency (RF) spin-flip coils, the magnetic shield, and the zero field coupling coils. The RF-flippers with larger beam windows allow for an improved neutron flux transfer from the source to the sample and further to the analyzer. The larger beam cross sections permit higher coil inclination angles and enable measurements on dispersive excitations with a larger slope of the dispersion. Due to the compact design of the spin-echo units in combination with the increased coil tilt angles, the accessible momentum-range in the Larmor diffraction mode is substantially enlarged. In combination with the redesigned components of the FLEXX spectrometer, including the guide, the S-bender polarizer, the double focusing monochromator, and a Heusler crystal analyzer, the count rate increased by a factor of 15.5, and the neutron beam polarization is enhanced. The improved performance extends the range of feasible experiments, both for inelastic scattering on excitation lifetimes in single crystals, and for high-resolution Larmor diffraction. The experimental characterization of the instrument components demonstrates the reliable performance of the new neutron resonance spin-echo option, now available for the scientific community at FLEXX.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Electromagnetic effects on turbulent transport in high-performance ASDEX Upgrade discharges

Modern tokamak H-mode discharges routinely operate at high plasma beta. Dedicated experiments performed on multiple machines measure contradicting dependence of the plasma confinement on this important parameter. In view of designing high-performance scenarios for next-generation devices like ITER, a fundamental understanding of the involved physics is crucial. Theoretical results—most of which have been obtained for simplified setups—indicate that increased beta does not only modify the characteristics of microturbulence but also potentially introduces fundamentally new physics. Empowered by highly accurate measurements at ASDEX Upgrade, the GENE turbulence code is used to perform a comprehensive gyrokinetic study of dedicated H-Mode plasmas. We find the stabilization of ion-temperature-gradient driven turbulence to be the most pronounced beta effect in these experimentally relevant cases. The resulting beta-improved core confinement should thus be considered for extrapolations to future machines.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Gyrokinetic studies of core turbulence features in ASDEX Upgrade H-mode plasmas

Gyrokinetic validation studies are crucial for developing confidence in the model incorporated in numerical simulations and thus improving their predictive capabilities. As one step in this direction, we simulate an ASDEX Upgrade discharge with the GENE code, and analyze various fluctuating quantities and compare them to experimental measurements. The approach taken is the following. First, linear simulations are performed in order to determine the turbulence regime. Second, the heat fluxes in nonlinear simulations are matched to experimental fluxes by varying the logarithmic ion temperature gradient within the expected experimental error bars. Finally, the dependence of various quantities with respect to the ion temperature gradient is analyzed in detail. It is found that density and temperature fluctuations can vary significantly with small changes in this parameter, thus making comparisons with experiments very sensitive to uncertainties in the experimental profiles. However, cross-phases are more robust, indicating that they are better observables for comparisons between gyrokinetic simulations and experimental measurements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

A new compact solid-state neutral particle analyser at ASDEX Upgrade: Setup and physics modeling

At ASDEX Upgrade (AUG), a new compact solid-state detector has been installed to measure the energy spectrum of fast neutrals based on the principle described by Shinohara et al. [Rev. Sci. Instrum. 75, 3640 (2004)]. The diagnostic relies on the usual charge exchange of supra-thermal fast-ions with neutrals in the plasma. Therefore, the measured energy spectra directly correspond to those of confined fast-ions with a pitch angle defined by the line of sight of the detector. Experiments in AUG showed the good signal to noise characteristics of the detector. It is energy calibrated and can measure energies of 40-200 keV with count rates of up to 140 kcps. The detector has an active view on one of the heating beams. The heating beam increases the neutral density locally; thereby, information about the central fast-ion velocity distribution is obtained. The measured fluxes are modeled with a newly developed module for the 3D Monte Carlo code F90FIDASIM [Geiger et al., Plasma Phys. Controlled Fusion 53, 65010 (2011)]. The modeling allows to distinguish between the active (beam) and passive contributions to the signal. Thereby, the birth profile of the measured fast neutrals can be reconstructed. This model reproduces the measured energy spectra with good accuracy when the passive contribution is taken into account.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Note: Upgrade of electron cyclotron emission imaging system and preliminary results on HL-2A tokamak

The electron cyclotron emission imaging system on the HL-2A tokamak has been upgraded to 24 (poloidally) × 16 (radially) channels based on the previous 24 × 8 array. The measurement region can be flexibly shifted due to the independence of the two local oscillator sources, and the field of view can be adjusted easily by changing the position of the zoom lenses. The temporal resolution is about 2.5 μs and the achievable spatial resolution is 1 cm. After laboratory calibration, it was installed on HL-2A tokamak in 2014, and the local 2D mode structures of MHD activities were obtained for the first time.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Charge breeder for the SPIRAL1 upgrade: Preliminary results

In the framework of the SPIRAL1 upgrade under progress at the GANIL lab, the charge breeder based on a LPSC Phoenix ECRIS, first tested at ISOLDE has been modified to benefit of the last enhancements of this device from the 1+/n+ community. The modifications mainly concern the 1 + optics, vacuum techniques, and the RF—buffer gas injection into the charge breeder. Prior to its installation in the midst of the low energy beam line of the SPIRAL1 facility, it has been decided to qualify its performances and several operation modes at the test bench of LPSC lab. This contribution shall present preliminary results of experiments conducted at LPSC concerning the 1 + to n+ conversion efficiencies for noble gases as well as for alkali elements and the corresponding transformation times.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Real time capable infrared thermography for ASDEX Upgrade

Infrared (IR) thermography is widely used in fusion research to study power exhaust and incident heat load onto the plasma facing components. Due to the short pulse duration of today’s fusion experiments, IR systems have mostly been designed for off-line data analysis. For future long pulse devices (e.g., Wendelstein 7-X, ITER), a real time evaluation of the target temperature and heat flux is mandatory. This paper shows the development of a real time capable IR system for ASDEX Upgrade. A compact IR camera has been designed incorporating the necessary magnetic and electric shielding for the detector, cooler assembly. The camera communication is based on the Camera Link industry standard. The data acquisition hardware is based on National Instruments hardware, consisting of a PXIe chassis inside and a fibre optical connected industry computer outside the torus hall. Image processing and data evaluation are performed using real time LabVIEW.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Progress in controlling ICRF-edge interactions in ASDEX upgrade

RF measurements during variation of the strap voltage balance of the original 2-strap ICRF antenna in ASDEX Upgrade at constant power are consistent with electromagnetic calculations by HFSS and TOPICA, more so for the latter. RF image current compensation is observed at the antenna limiters in the experiment at a local strap voltage of about half of the value of the remote strap, albeit with a non-negligible uncertainty in phasing. The RF-specific tungsten (W) source at the broad-limiter 2-strap antenna correlates strongly with the RF voltage at the local strap at the locations not connected to opposite side of the antenna along magnetic field lines. The trends of the observed increase of the RF loading with injection of local gas are well described by a combined EMC3-Eirene – FELICE calculations, with the most efficient improvement confirmed for the outer-midplane valves, but underestimated by about 1/3. The corresponding deuterium density tailoring is also likely responsible for the decrease of local W sources observed in the experiment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Estimation of sheath potentials in front of ASDEX upgrade ICRF antenna with SSWICH asymptotic code

Multi-megawatt Ion Cyclotron Range of Frequencies (ICRF) heating became problematic in ASDEX Upgrade (AUG) tokamak after coating of ICRF antenna limiters and other plasma facing components by tungsten. Strong impurity influx was indeed produced at levels of injected power markedly lower than in the previous experiments. It is assumed that the impurity production is mainly driven by parallel component of Radio-Frequency (RF) antenna electric near-field E// that is rectified in sheaths. In this contribution we estimate poloidal distribution of sheath Direct Current (DC) potential in front of the ICRF antenna and simulate its relative variations over the parametric scans performed during experiments, trying to reproduce some of the experimental observations. In addition, relative comparison between two types of AUG ICRF antenna configurations, used for experiments in 2014, has been performed. For this purpose we use the Torino Polytechnic Ion Cyclotron Antenna (TOPICA) code and asymptotic version of the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code. Further, we investigate correlation between amplitudes of the calculated oscillating sheath voltages and the E// fields computed at the lateral side of the antenna box, in relation with a heuristic antenna design strategy at IPP Garching to mitigate RF sheaths.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Simulations of gas puff effects on edge density and ICRF coupling in ASDEX upgrade using EMC3-Eirene

Simulations were carried out with the 3D plasma transport code EMC3-EIRENE, to study the deuterium gas (D{sub 2}) puff effects on edge density and the coupling of Ion Cyclotron Range of Frequency (ICRF) power in ASDEX Upgrade. Firstly we simulated an inter-ELM phase of an H-mode discharge with a moderate (1.2 × 10{sup 22} electrons/s) lower divertor gas puff. Then we changed the gas source positions to the mid-plane or top of machine while keeping other conditions the same. Cases with different mid-plane or top gas valves are investigated. Our simulations indicate that compared to lower divertor gas puffing, the mid-plane gas puff can enhance the local density in front of the antennas most effectively, while a rather global (toroidally uniform) but significantly smaller enhancement is found for top gas puffing. Our results show quantitative agreement with the experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Ion cyclotron resonance heating systems upgrade toward high power and CW operations in WEST

The design of the WEST (Tungsten-W Environment in Steady-state Tokamak) Ion cyclotron resonance heating antennas is based on a previously tested conjugate-T Resonant Double Loops prototype equipped with internal vacuum matching capacitors. The design and construction of three new WEST ICRH antennas are being carried out in close collaboration with ASIPP, within the framework of the Associated Laboratory in the fusion field between IRFM and ASIPP. The coupling performance to the plasma and the load-tolerance have been improved, while adding Continuous Wave operation capability by introducing water cooling in the entire antenna. On the generator side, the operation class of the high power tetrodes is changed from AB to B in order to allow high power operation (up to 3 MW per antenna) under higher VSWR (up to 2:1). Reliability of the generators is also improved by increasing the cavity breakdown voltage. The control and data acquisition system is also upgraded in order to resolve and react on fast events, such as ELMs. A new optical arc detection system comes in reinforcement of the V{sub r}/V{sub f} and SHAD systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Upgrading multilayer zone plate technology for hard x-ray focusing

Multilayer zone plate (MZP) technology for hard X-ray focusing was upgraded and its focusing performance was evaluated using 20-keV X-rays at the synchrotron beamline (BL24XU) of SPring-8. The MZP consists of MoSi{sub 2} and Si layers alternately deposited on a glass fiber by magnetron sputtering so that all zone boundaries satisfy the Fresnel zone configuration. The focused beam was evaluated using knife-edge scanning in which the measured intensity distribution is identical to the line spread function (LSF) in the focal plane. The focused beamsize of about 30 nm was estimated by oscillation peaks observed in the measured LSF according to Rayleigh’s criterion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Progress of projection computed tomography by upgrading of the beamline 37XU of SPring-8

Beamline 37XU at SPring-8 has been upgraded for nano-focusing applications. The length of the beamline has been extended to 80 m. By utilizing this length, the beamline has advantages for experiments such as X-ray focusing, X-ray microscopic imaging and X-ray computed tomography. Projection computed tomography measurements were carried out at experimental hutch 3 located 80 m from the light source. CT images of a microcapsule have been successfully obtained with a wide X-ray energy range.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Influence of additives on the increase of the heating value of Bayah’s coal with upgrading brown coal (UBC) method

UBC (upgrading brown coal) is a method of improving the quality of coal by using oil as an additive. Through processing in the oil media, not just the calories that increase, but there is also water repellent properties and a decrease in the tendency of spontaneous combustion of coal products produced. The results showed a decrease in the water levels of natural coal bayah reached 69%, increase in calorific value reached 21.2%. Increased caloric value and reduced water content caused by the water molecules on replacing seal the pores of coal by oil and atoms C on the oil that is bound to increase the percentage of coal carbon. As a result of this experiment is, the produced coal has better calorific value, the increasing of this new calorific value up to 23.8% with the additive waste lubricant, and the moisture content reduced up to 69.45%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Molybdenum carbide nanoparticles as catalysts for oil sands upgrading: Dynamics and free-energy profiles

There is no doubt that a huge gap exists in understanding heterogeneous catalysis between a cluster model of a few atoms and a bulk model of periodic slabs. Nanoparticles, which are crucial in heterogeneous catalysis in industry, lie in the middle of the gap. We present here our work on the computational modelling of molybdenum carbide nanoparticles (MCNPs) as the catalysts for the upgrading of oil sands in the in-situ environment, using benzene hydrogenation as a model reaction. With a cluster model, efforts were first made to understand the mechanism of the reaction with a density functional theory (DFT) study on the adsorption of benzene and its hydrogenation product – cyclohexane, as well as the cyclic hydrogenation reaction intermediates on the Mo{sub 2}C(0001) surface. From the thermodynamic data, along with literature information, it was found that the benzene hydrogenation reaction on molybdenum carbide happens most likely through a Langmuir-Hinshelwood mechanism with the gradual lifting up of the benzene molecule. The electron localization function (ELF) was then used to help understand the nature of the interactions between the MCNPs, identifying strong multi-center interactions between the adsorbates and the MCNPs. To enable the treatment of larger nanoparticles, a fast semi-empirical density functional tight-binding (DFTB) method was parameterized. With this method, the potential energy profiles of benzene hydrogenation reactions on different sizes of MCNPs are calculated. The study was then extended to consider a MCNP embedded in solvent (benzene), using a quantum mechanical (DFTB) / molecular mechanical approach. Calculations on the free energies profiles with the umbrella sampling method show that the entropy of the MCNPs and the solvent are essential in understanding the catalytic activity of the transition metal related nanoparticles for solid/liquid heterogeneous catalysis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Poloidal asymmetric flow and current relaxation of ballooned transport during I-phase in ASDEX Upgrade

Turbulence driven poloidal asymmetric parallel flow and current perturbations are studied for tokamak plasmas of circular geometry. Whereas zonal flows can lead to in-out asymmetry of parallel flows and currents via the Pfirsch–Schlüter mechanism, ballooned transport can result in an up-down asymmetry due to the Stringer spin-up mechanism. Measurements of up-down asymmetric parallel current fluctuations occurring during the I-phase in ASDEX Upgrade are not responses to the equilibrium by the Pfirsch–Schlüter current, but can be interpreted as a response to strongly ballooned plasma transport coupled with the Stringer spin-up mechanism. A good agreement of the experimental measured limit-cycle frequencies during I-phase with the Stringer spin-up relaxation frequency is found.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗