•Fast IR thermographic system was designed and partially commissioned on COMPASS.•Near SOL λq is constant during a sawtooth cycle.•Fast modulation of first wall heat loading due to runaway electrons ...was observed.
A new fast infrared camera was purchased on the COMPASS tokamak recently. It is equipped with a medium wavelength infrared (3–5mm) InSb detector and is capable of reaching framerate up to 1.9kHz in full frame acquisition mode (320×256px.) and up to 90kHz in sub-windowed mode (64×4px.).
First experimental measurements of plasma heat flux to inner and outer wall limiters of the COMPASS tokamak using the new camera are presented. Time evolution of parallel heat flux during sawtooth instability is studied showing strong modulation of the heat flux absolute value whilst keeping constant its radial decay length. Fast modulation of outboard midplane limiter heat loading due to runaway electrons is also presented.
The camera will be part of a new fast divertor thermographic system with exceptional spatial resolution (∼0.6–1.3mm/px. on the target plane, 0.04–0.14mm/px. mapped to the outer midplane) with a possibility of measurements of radial profiles on the divertor with 320×4px. with temporal resolution better than 20μs. A design of the foreseen optical divertor system is described together with a design of a special divertor graphite tile used for the IR thermography, that will allow in-situ surface emissivity calibration.
•Main constraints influencing the conceptual design of diagnostics for COMPASS-U were identified.•Diagnostic solutions for the hot vacuum vessel, high plasma densities and high heat flux densities ...are proposed.•Spatial constraints at COMPASS-U are reviewed and possible solutions indicated.
COMPASS-U, a high magnetic field tokamak with hot walls, will be designed and built at IPP Prague. Unique features of this new device bring noticeable constraints and requirements on plasma diagnostics, which make their development highly demanding. In this paper, the main expected constraints influencing the conceptual design of diagnostic tools for COMPASS-U (high temperature of the vacuum vessel, high plasma density, high heat flux density, strong auxiliary plasma heating, spatial constraints, liquid metals in the divertor) are reviewed and possible solutions are indicated.
Although numerous clinical, laboratory, and pharmacological variables have been reported as significant risk factors for critical illness polyneuromyopathy (CIPM), there is still no consensus on the ...aetiology of this condition. Objectives of the study were to assess the clinical and electrophysiological incidence and risk factors for CIPM.A cohort of critically ill patients was observed prospectively for a one-month period and the association between neuromuscular involvement and various potential risk factors was evaluated. Sixty one critically ill patients completed the follow-up (30 women, 31 men, median age 59 years).CIPM development was detected clinically in 17 patients (27.9 %) and electrophysiologically in 35 patients (57.4 %). CIPM was significantly associated with the presence and duration of systemic inflammatory response syndrome and the severity of multiple, respiratory, central nervous, and cardiovascular organ failures. The median duration of mechanical ventilation was significantly longer in patients with CIPM than in those without (16 vs 3 days, p<0.001). Independent predictors of CIPM obtainable within the 1(st) week of critical illness were the admission sequential organ failure assessment score (odds ratio OR, 1.15; 95% confidence interval CI, 1.02-1.36), the 1(st) week total sequential organ failure assessment scores (OR, 1.14; 95 % CI, 1.06-1.46) and the 1(st) week duration of systemic inflammatory response syndrome (OR, 1.05; 95% CI, 1.01-1.15). They were able to correctly predict the development of CIPM at the end of the 1(st) week in about 80% of critically ill cases.In conclusion, the presence and duration of systemic inflammatory response syndrome and the severity of multiple and several organ failures are associated with increased risk of the development of CIPM.
Kinetic model of the COMPASS tokamak SOL Tskhakaya, D.; Adamek, J.; Dimitrova, M. ...
Nuclear materials and energy,
March 2021, 2021-03-00, 2021-03-01, Letnik:
26
Journal Article
Recenzirano
Odprti dostop
•Kinetic effects are significant in the inner divertor plasma. Parallel heat flux in the entire SOL is strongly non-local.•Normalized power loads to the ID are above the classical values and are ...caused by non-Maxwellian super-thermal electrons.•Different divertor current regimes do not influence overall SOL parameters, except those of the divertor sheath.•Ions in the divertors plasma are colder than the electrons.•Modelling results are in a reasonable agreement with the experimental measurements.
In this work we report on results of full size kinetic modelling of the COMPASS tokamak SOL. Presented simulations indicate, that i. kinetic effects are significant in the inner divertor (ID) plasma; ii. normalized power loads to the ID are above the classical values and are caused by non-Maxwellian super-thermal electrons; iii. different divertor current regimes do not influence overall SOL parameters, except those of the divertor sheath; iv. ions at the divertors plasma are colder than the electrons; v. parallel heat transport is strongly non-local. Modelling results are in a reasonable agreement with the experimental measurements.
The narrow scrape-off layer power component observed in COMPASS inner wall limiter circular discharges by means of IR thermography is investigated by Langmuir probes embedded in the limiter. The ...power flux profiles are in good agreement with IR observations and can be described by a double-exponential decay with a short decay length (<5mm) just outside the separatrix and a longer one (∼50mm) for the rest of the profile in the main scrape-off layer. Non-ambipolar currents measured at the limiter apex play a relatively modest role in the formation of the narrow component. The fraction of the deposited power due to non-ambipolarity varies between 2% and 45%. On the other hand, the measured power widths are roughly consistent in magnitude with a model that takes into account drift effects, suggesting these effects may be dominant.
•Power exhaust of a CPS liquid metal divertor target in ELMy conditions is reported.•Good power handling of Li and LiSn up to ~12 MW/m2 and ELM energy fluence 15 kJ/m2.•No droplets directly ejected ...from the CPS mesh and no damage of the latter observed.•No contamination of the core and SOL plasmas by tin was observed.•Neutral Li is very well localized in the close vicinity of the CPS mesh.
Power handling experiments with a special liquid metal divertor module based on the capillary porous system technology were performed in the tokamak COMPASS. The performance of two metals (Li and LiSn alloy) were tested for the first time in a divertor under ELMy H-mode conditions. No damage of the capillary mesh and a good exhaust capability were observed for both metals in two separate experiments with up to 12 MW/m2 of deposited perpendicular, inter-ELM steady-state heat flux and with ELMs of relative energy ~3% and a local peak energy fluence at the module ~15 kJ.m−2. No droplets were directly ejected from the mesh top surface and for the LiSn experiment, no contamination of the core and SOL plasmas by Sn was observed. The elemental depth profile analysis of 14 stainless-steel samples located around the vacuum vessel for each experiment provides information about the migration of evaporated/redeposited liquid elements.
•The physics of toroidal gap heat loading is fully described.•Total heat flux can load either one or both sides (thus including shadowed side).•Power deposition on shadowed side confirmed ...experimentally on COMPASS.•Local non-ambipolarity plays a strong role in deposition pattern.•Electric field has small impact for Larmor radii larger than gap width.
Because the gaps between plasma-facing components in fusion devices are comparable in size to the ion Larmor radius (of the order of 1 mm), magnetic field line tracing, the so-called "optical approximation", cannot accurately predict the fine scale heat load distribution around the gap edges. Finite Larmor radius effects dominate ion deposition. The poloidal component of the ion flux striking the surface is always in the diamagnetic/EXB drift direction, meaning that ions preferentially load one side of the gap. Usually electrons can be described optically due to their smaller Larmor radius. Depending on the local inclination of magnetic flux surfaces, it is possible that ions and electrons wet the same side of the gap, or opposite sides. Two-dimensional particle-in-cell simulations and dedicated experiments performed in the COMPASS tokamak are used to better understand processes responsible for plasma deposition on the sides of toroidal gaps between castellated plasma-facing components in tokamaks. The different contributions of the total incoming flux along a toroidal gap have been observed experimentally for the first time in COMPASS. These experimental results confirm the model predictions, demonstrating that in specific cases the heat deposition does not necessarily follow the optical approximation. The role played by electric fields in the deposition pattern is marginal, contrary to local non-ambipolarity that can change the asymmetrical plasma deposition from one side of the toroidal gap to the other.
Two small liquid metal targets based on the capillary porous structure were exposed to the divertor plasma of the tokamak COMPASS. The first target was wetted by pure lithium and the second one by a ...lithium-tin alloy, both releasing mainly lithium atoms (sputtering and evaporation) when exposed to plasma. Due to poorly conductive target material and steep surface inclination (implying the surface-perpendicular plasma heat flux 12–17 MW/m2) for 0.1–0.2 s, the LiSn target has reached 900 °C under ELMy H-mode. A model of heat conduction is developed and serves to evaluate the lithium sputtering and evaporation and, thus, the surface cooling by the released lithium and consequent radiative shielding. In these conditions, cooling of the surface by the latent heat of vapor did not exceed 1 MW/m2. About 1019 lithium atoms were evaporated (comparable to the COMPASS 1 m3 plasma deuterium content), local Li pressure exceeded the deuterium plasma pressure. Since the radiating Li vapor cloud spreads over a sphere much larger than the hot spot, its cooling effect is negligible (0.2 MW/m2). We also predict zero lithium prompt redeposition, consistent with our observation.
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