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The effect of alkyl side chain length on the formation of two semi-crystalline phases in low band gap conjugated polymers
No full textCharge carrier dynamics and photocatalytic activity of {111} and {100} faceted Ag3PO4 particles
Get PDFSilver orthophosphate is a highly promising visible light photocatalyst with high quantum yield for solar driven water oxidation. Recently, the performance of this material has been further enhanced using facet-controlled synthesis. The tetrahedral particles with {111} exposed facets demonstrate higher photocatalytic performance than the cubic particles with {100} exposed facets. However, the reason behind this large difference in photocatalytic performance is still not understood. In this work, we study the free charge carrier dynamics, such as mobility, lifetime, and diffusion lengths, for the {111}-faceted tetrahedral and the {100}-faceted cubic particles using time-resolved microwave conductivity measurements. An order of magnitude higher charge carrier mobility and diffusion length are found for the tetrahedral particles as compared to the cubic particles. The differences in crystal structure, surface composition, and optical properties are investigated in order to understand how these properties impact the charge carrier dynamics and the photocatalytic performance of differently faceted particles.</p
A novel frequency domain maximum likelihood approach for estimating transport coefficients in cylindrical geometry for nuclear fusion devices
No full textThis paper introduces a novel maximum likelihood approach to determine the local thermal transport coefficients belonging to diffusion and convection from excitation (perturbative) transport experiments. It extends previous work developed for linear (slab) geometry to cylindrical (toroidal) geometry for fusion reactors. The previous linear geometry approach is based on analytic solutions of the partial differential equation. However, for cylindrical geometries with convection the analytic solutions are confluent hypergeometric functions (CHFs) with complex valued arguments. Most numerical libraries do not support CHFs evaluation with complex valued arguments. Hence, this paper proposes the use of an ultra-fast transfer function evaluation based on sparse numerical solutions for the discretized partial differential equation. This solution is implemented in MATLAB © and incorporated in the frequency domain Maximum Likelihood Estimation framework. Consequently, transport coefficients can be estimated consistently when measurements are perturbed by coloured and spatially correlated noise
First efforts in numerical modeling of tungsten migration in WEST with SolEdge2D-EIRENE and ERO2.0
No full textThe first simulations of tungsten migration in WEST are performed with the SolEdge2D-EIRENE and ERO2.0 codes to support experimental investigations into the erosion of plasma-facing components and plasma impurity content. The impact of varying the background density on (i) the amount of tungsten penetrating the confined plasma, (ii) the promptly redeposited fraction, and (iii) the erosion and deposition patterns on the wall, is investigated under the working assumptions of a simplified toroidally symmetric wall contour, typical L-mode values of the transport coefficients, and deuterium plasma with a 1% oxygen content. The lower divertor is found to be the main zone of net tungsten erosion and deposition. This pattern is reduced at high background density due to the higher promptly redeposited fraction
Selection of molybdenum lines by quantitative analysis of molybdenum- zirconium-titanium alloy by CF-LIBS for future fusion applications
No full textMolybdenum and its alloys have been chosen as substrate and support material for tungsten thin layers at special limiters and divertors parts of tokamak devices. These Molybdenum parts of the tokamak walls are used for mapping and quantification of material migration and redeposition. In this work, we used Laser Induced Breakdown Spectroscopy (LIBS) as a diagnostic method to analyse Mo-Zr-Ti alloy (TZM) under three different ambient conditions expected in a tokamak in between periods of plasma operation. LIBS spectra were measured under air atmosphere and under Argon and Nitrogen flow at the laser spot on the sample. The resulting plasma plume was created using Nd:YAG (1064 nm) laser operating at the fourth harmonic frequency (266 nm). Atomic and ionic spectral lines of Mo, Ti and Zr were selected from spectra and used for analysis. The evolution of plasma parameters – electron density (ne) and electron temperature (Te) - has been observed by choosing different gate windows and delays relative to the laser pulse. Finally, the elemental concentration of the TZM sample has been calculated by the calibration free LIBS approach. The results are showing that most suitable conditions for elemental analysis are gate delay and gate width equal to 750, 1000, 1500 ns respectively, where we observed similar elementary concentrations in all three conditions
Scrape-off layer transport and filament characteristics in high-density tokamak regimes
No full textA detailed cross-device investigation on the role of filamentary dynamics in high-density regimes has been performed within the EUROfusion framework, comparing the ASDEX Upgrade (AUG) and TCV tokamaks. Both devices run density ramp experiments at different levels of plasma current, keeping the toroidal field or q95 constant in order to disentangle the role of the parallel connection length and the current. During the scan at a constant toroidal field, in both devices the scrape-off layer (SOL) profiles tend to develop a clear SOL density shoulder at a lower edge density whenever the current is reduced. Different current behaviour is substantially reconciled in terms of the edge density normalized to the Greenwald fraction. During the scan at constant q95 AUG exhibits similar behaviour, whereas in TCV no upstream profile modification signature has been observed at lower current levels. The latter behaviour has been ascribed to the lack of target density rollover. The relation between the upstream density profile modification and detachment condition has been investigated. For both devices the relation between blob size and the SOL density e-folding length is found independent of the plasma current, with the observation of a clear increase in blob size and the edge density normalized to a Greenwald fraction. ASDEX Upgrade has also explored filamentary behaviour in the H-mode. The experiments in AUG have focused on the role of neutrals, performing discharges with and without cryogenic pumps, highlighting how high neutral pressure, not only in the divertor but also at the midplane, is needed in order to develop an H-mode SOL profile shoulder in AUG.</p
Deuterium retention in Sn-filled samples exposed to fusion-relevant flux plasmas
No full textTin (Sn) is an attractive option for a liquid metal wall material for future fusion reactors. Control of tritium inventory is key for the successful operation of these reactors, but little data exists up until now on hydrogen isotope retention in Sn. Free surface Sn targets and Sn-based capillary porous structure targets were exposed to deuterium (D) plasma in nano-PSI and magnum-PSI respectively. The retained D inventory was determined using the methods of thermal desorption spectroscopy and nuclear reaction analysis. The retention dependence is somewhat complex due to the mixed composition of the exposed samples as well as their liquid nature. The D retained in both types of Sn targets was found to increase with increasing D plasma fluence. For free surface liquid Sn targets, both thermal desorption spectroscopy and nuclear reaction analysis measurements showed a negative relationship between D retention and sample temperature. For capillary porous structure Sn targets, D retained in the top layer measured by nuclear reaction analysis decreased with temperature while the total D retained measured by thermal desorption spectroscopy remained approximately constant. By extracting pure Sn pieces from the targets it was found that the amount of D retained in pure Sn was much lower than that in the whole Sn-based targets and was estimated to be about 10−7–10−4 D/Sn. D retained at the Sn-wall interface was found to dominate the total amount of D retained in the whole sample and observed cavities between deposited Sn droplets and the wall are the leading candidates responsible for this. Cavity formation is proposed to be the main retention mechanism for D in liquid Sn targets, although enhanced solubility leading to supersaturation under a D plasma environment is mainly responsible for the observed higher D retention in pure Sn compared with normal solubility under D gas. When compared with tungsten, D in Sn samples is of the same order of magnitude at temperatures below 300 °C, but at higher temperatures at least one to two orders of magnitude higher, most likely due to D trapped in cavities
Multi-Scale Interactions of Microtearing Turbulence in the Tokamak Pedestal
Get PDFMicrotearing turbulence in an idealized pedestal scenario is found to saturate via zonal fields, while also exciting strong zonal flows; a concurrent upshift of the non-linear critical gradient is observed. The zonal flows cause electron-temperature-gradient-driven turbulence to be ameliorated. When applying resonant magnetic perturbations, the prompt charge loss off the flux surface erodes the zonal flow, leading to higher electron-scale fluxes, while leaving microtearing saturation physics unaffected.</p
Extended Full-MHD Simulation of Non-linear Instabilities in Tokamak Plasmas
No full textNon-linear MHD simulations play an essential role in active research and understanding of tokamak plasmas for the realisation of a fusion power plant. The development of MHD codes like JOREK is a key aspect of this research effort. In this paper, we present an operational version of the full-MHD model implemented in JOREK, a significant advancement from the reduced-MHD model used for previous studies, where assumptions were made on the perpendicular dynamics and the toroidal magnetic field. The final model is presented in detail, and benchmarks are performed using both linear and non-linear simulations, including comparisons between the new full-MHD model of JOREK and the previously extensively studied reduced-MHD model, as well as results from the linear full-MHD code CASTOR3D. For the cases presented, this new JOREK full-MHD model is numerically and physically reliable, even without the use of numerical stabilisation methods. Non-linear modelling results of typical tokamak instabilities are presented, including disruption and ELM physics, most relevant to current open issues concerning future tokamaks like ITER and DEMO.</p