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Effect of Bromine Complexing Agents on Membrane Performance in Hydrogen Bromine Flow Batteries
No full textValidation of the Fokker-Planck Approach to Vibrational Kinetics in CO2 Plasma
Get PDFThe Fokker-Planck (FP) approach to describe vibrational kinetics numerically is validated in this work. This approach is shown to be around 1000 times faster than the usual state-to-state (STS) method to calculate a vibrational distribution function (VDF) in stationary conditions. Weakly ionized, nonequilibrium CO2 plasma is the test case for this demonstration, in view of its importance for the production of carbon-neutral fuels. VDFs obtained through the resolution of an FP equation and through the usual STS approach are compared in the same conditions, considering the same kinetic data. The demonstration is shown for chemical networks of increasing generality in vibrational kinetics of polyatomic molecules, including V-V exchanges, V-T relaxation, intermode V-V\u27 reactions, and excitation through e-V collisions. The FP method is shown to be accurate to describe the vibrational kinetics of the CO2 asymmetric stretching mode, while being much faster than the STS approach. In this way, the quantitative validity of the FP approach in vibrational kinetics is assessed, making it a fully viable alternative to STS solvers, that can be used with other processes, molecules, and physical conditions.</p
An improved understanding of the roles of atomic processes and power balance in divertor target ion current loss during detachment
No full textThe process of divertor detachment, whereby heat and particle fluxes to divertor surfaces are strongly diminished, is required to reduce heat loading and erosion in a magnetic fusion reactor to acceptable levels. In this paper, the physics leading to the decrease of the total divertor ion current (I t), or \u27roll-over\u27, is experimentally explored on the TCV tokamak through characterization of the location, magnitude and role of the various divertor ion sinks and sources including a complete analysis of particle and power balance. These first measurements of the profiles of divertor ionisation and hydrogenic radiation along the divertor leg are enabled through novel spectroscopic techniques.
Over a range in TCV plasma conditions (plasma current and electron density, with/without impurity-seeding) the I t roll-over is ascribed to a drop in the divertor ion source; recombination remains small or negligible farther into the detachment process. The ion source reduction is driven by both a reduction in the power available for ionization, P recl, and concurrent increase in the energy required per ionisation, E ion: this effect of power available on the ionization source is often described as \u27power starvation\u27 (or \u27power limitation\u27). The detachment threshold is found experimentally (in agreement with analytic model predictions) to be ~P recl/I t E ion ~ 2, corresponding to a target electron temperature, T t ~ E ion/γ where γ is the sheath transmission coefficient. The target pressure reduction, required to reduce the target ion current, is driven both by volumetric momentum loss as well as upstream pressure loss.
The measured evolution through detachment of the divertor profile of various ion sources/sinks as well as power losses are quantitatively reproduced through full 2D SOLPS modelling through the detachment process as the upstream density is varied
On the homocoupling of trialkylstannyl monomers in the synthesis of diketopyrrolopyrrole polymers and its effect on the performance of polymer-fullerene photovoltaic cells
No full textTesting of a high temperature radiatively cooled Li/Ta heat pipe in Magnum-PSI
No full textIn this paper we present results from plasma testing and thermal analysis of a lithium filled tubular heat pipe used as a replaceable plasma facing component (PFC) with no direct cooling. The tantalum envelope (19 mm diameter by 197 mm long) was heated on its side wall using a hydrogen plasma beam in the linear plasma device Magnum-PSI. A single continuous plasma pulse lasting ˜2 h was carried out with the isothermal zone of the heat pipe operating at a temperature of ˜1000 °C for the whole time with the main heat removal via thermal radiation. Target tilting was used to vary the peak surface heat flux in the range 7.5–13 MW/m2. The tilting also increased the magnetic field component normal to the return flow of lithium via the sintered niobium wick to ˜0.85 T. Near infra-red thermography was used to measure the surface temperature. Heating power was increased until liquid lithium escaped through a crack in the heat pipe near the beam center. The impact of the lithium leak on the plasma was benign compared to that expected from leaks in helium or water cooled PFCs. The operating limit due to magnetohydrodynamic effects is calculated
Nearing final design of the ITER EC H&CD Upper Launcher
No full textThe ITER ECRH system consists of 24 gyrotrons with up to 24 MW installed millimeter wave heating power at 170 GHz, power supplies, control system, transmission lines, one Equatorial and the four Upper Launchers. With its high frequency and small beam focus the ECRH has the unique capability of driving locally current. While the Equatorial Launcher mainly acts for central heating and current profile shaping, the Upper Launchers aim on suppressing MHD instabilities, especially neoclassical tearing modes (NTM) triggering plasma disruptions. The Upper Launchers inject millimeter waves through a quasi-optical section consisting of three fixed and the front steering mirror set. The eight overlapping beams have focal points optimized for suppression of the q = 3/2 and q = 2/1 NTMs. Several project change requests required the redesign of the Upper Launchers and the connected ex-vessel system. This redesign includes a new boundary geometry of the launchers as well as a newly designed cooling system for the Blanket Shield Module (BSM), a modified flange of the BSM to the structural main frame and a refined optical design. Additionally shield blocks with integrated in-vessel waveguides were added and the closure plate with waveguide and supply line feedthroughs was adapted. Further changes, not all caused by PCRs, include newly designed ex-vessel waveguide components with a reduced aperture and redesigned ultra low-loss CVD diamond windows. Finally several components originally foreseen as off-the-shelf components have become part of the design scope. The new launcher design status is presented with selected results on numerical design validation
Waves in a warm pair plasma: a relativistically complete two-fluid analysis
Get PDFWe present an ideal two-fluid wave mode analysis for a pair plasma, extending an earlier study for cold conditions to the warm pair plasma case. Starting from the completely symmetrized means for writing the governing linearized equations in the pair fluid rest frame, we discuss the governing dispersion relation containing all six pairs of forward and backward propagating modes, which are conveniently labelled as S, A, F, M, O and X. These relate to the slow (S), Alfven (A) and fast (F) magnetohydrodynamic waves, include a modified (M) electrostatic mode, as well as the electromagnetic O and X branches. In the dispersion relation, only two parameters appear, which define the pair plasma magnetization E2 E[0, infinity] and the squared pair plasma sound speed v2, measured in units of the light speed c. The description is valid also in the highly relativistic regime, where either a high magnetization and/or a relativistic temperature (hence sound speed) is reached. We recover the exact relativistic single-fluid magnetohydrodynamic expressions for the S, A and F families in the low wavenumber–frequency regime, which can be obtained for any choice of the equation of state. We argue that, as in a cold pair plasma, purely parallel or purely perpendicular propagation with respect to the magnetic field vector B is special, and near-parallel or near-perpendicular orientations demonstrate avoided crossings of branches at computable wavenumbers and frequencies. The complete six-mode phase and group diagram views are provided as well, visually demonstrating the intricate anisotropies in all wave modes, as well as their transformations. Analytic expressions for all six wave group speeds at both small and large wavenumbers complement the analysis.</p
Density peaking in JET - determined by fuelling or transport?
No full textCore density profile peaking and electron particle transport have been extensively studied by performing several dimensionless collisionality (υ *) scans with other matched dimensionless profiles in various plasma operation scenarios on the Joint European Torus (JET). This is the first time when electron particle transport coefficients in the H-mode have been measured on JET with high resolution diagnostics, and therefore we are in a position to distinguish between the neutral beam injection (NBI) source and inward electron particle pinch in contributing to core density peaking. The NBI particle source is found to contribute typically 50%–60% to the electron density peaking in JET H-mode plasmas where T e/T i ~ 1 or smaller and at υ * = 0.1–0.5 (averaged between r/a = 0.3–0.8), and being independent of υ * within that range. In these H-mode plasmas, the electron particle transport coefficients, D e and v e, are small, thus giving rise to the large influence of NBI fueling with respect to transport effect on peaking. In L-mode plasma conditions, the role of the NBI source is small, typically 10%–20%, and the electron particle transport coefficients are large. These dimensionless υ * scans give the best possible data for model validation. TGLF simulations are in good agreement with the experimental results with respect to the role of NBI particle source versus inward pinch in affecting density peaking, both for the H-mode and L-mode υ * scans. It predicts, similarly to experimental results, that typically about half of the peaking originates from the NBI fuelling in the H-mode and 10%–20% in the L-mode. GENE simulation results also support the key role of NBI fuelling in causing a peaked density profile in JET H-mode plasma (T e/T i ~ 1 and υ * = 0.1–0.5) and, in fact, give an even higher weight on NBI fuelling than that experimentally observed or predicted by TGLF. For the non-fuelled H-mode plasma at higher T e/T i = 1.5 and lower β N and υ *, both TGLF and GENE predict peaked density profiles, therefore agreeing well with experimental steady-state density peaking. Overall, the various modelling results give a fairly good confidence in using TGLF and GENE in predicting density peaking in quite a wide range of plasma conditions in JET
Surface nano structures on W surface exposed to low-energy high flux D plasma
No full textThe surface nano structures on W surface exposed to low-energy D plasma was studied by transmission electron microscopy. It was found that the surface nano structures on W surface induced by D plasma were mainly due to two reasons. First, the subsurface nano-sized bubbles will induce nano scale blistering of the surface, resulting in surface nano morphology. The nano scale blistering behaviour is most obvious on [1 1 1] surface at low temperature (500 K). Secondly, during the plasma exposure, oxide layer on W surface will be sputtered by low energy D particles, and the sputtering can also induce nano structures on some surfaces. At low temperature (500 K), the surface nano structures were formed due to the nano scale blistering behaviour and the sputtering of surface oxide layer. At high temperature (1000 K), the surface nano structures were mainly caused by the sputtering of surface oxide layer
An Electrochemical Study on the Cathode of the Intermediate Temperature Tubular Sodium-Sulfur (NaS) Battery
Get PDFThe development of low-cost energy storage schemes is imminent in light of the ever-growing demand of electricity. Sodium-sulfur (NaS) batteries offer low-cost technology for energy storage applications due to the intrinsically high capacities of elemental sodium and sulfur as well as their abundant resources. Operating this battery technology on the intermediate range (130-200 degrees C) can lead to lower material costs, mitigate thermal management and safety issues and enhance cycle life. Herein, an electrochemical study on the cathode of the IT NaS cell is performed at 150 degrees C and a concentration range of 1.5 to 3 M sodium pentasulfide dissolved in tetraglyme, showing a robust long term performance (42 days of continuous cycling) with a volumetric energy density of 83 Wh L-1. Most importantly, the cell was eligible for a tenfold volume scale-up considerably enhancing its capacity (790 mAh) but in the same time somewhat hindered by mass transport, especially during the end of the discharge process as manifested by electrochemical impedance spectroscopy.</p