Evaluation and demonstration of a propellant quantity gaging system for auxiliary propulsion systems Final report

Bipropellant quantity gaging digital syste

Modeling of COMPASS tokamak divertor liquid metal experiments

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/m(2)) for 0.1-0.2 s, the LiSn target has reached 900 degrees 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/m(2). About 10(19) lithium atoms were evaporated (comparable to the COMPASS 1 m(3) 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/m(2)). We also predict zero lithium prompt redeposition, consistent with our observation.

Summary statistics in auditory perception

Sensory signals are transduced at high resolution, but their structure must be stored in a more compact format. Here we provide evidence that the auditory system summarizes the temporal details of sounds using time-averaged statistics. We measured discrimination of 'sound textures' that were characterized by particular statistical properties, as normally result from the superposition of many acoustic features in auditory scenes. When listeners discriminated examples of different textures, performance improved with excerpt duration. In contrast, when listeners discriminated different examples of the same texture, performance declined with duration, a paradoxical result given that the information available for discrimination grows with duration. These results indicate that once these sounds are of moderate length, the brain's representation is limited to time-averaged statistics, which, for different examples of the same texture, converge to the same values with increasing duration. Such statistical representations produce good categorical discrimination, but limit the ability to discern temporal detail.Howard Hughes Medical Institut

Modelling of charge-exchange induced NBI losses in the COMPASS Upgrade tokamak

The COMPASS Upgrade tokamak [1] will be a tokamak of major radius R0 = 0.894m with the possibility to reach high field (Bt ~ 5 T) and high current (Ip ~ 2 MA). The machine should see its first plasma in 2023 and H-mode plasma will be obtained from 2025. The main auxiliary heating system used to access H-mode will be 4MW of Neutral Beam Injection (NBI) power. The NBI will have a nominal injection energy of 80 keV, a maximum injection radius Rtan = 0.65m and will create a population of well-confined energetic D ions. In this contribution, our modelling studies the NBI deposition and losses when a significant edge background density of neutrals is assumed. We follow the fast particles in the 3D field generated by the 16 toroidal field (TF) coils using the upgraded EBdyna orbit solver. We have implemented a Coulomb collision operator similar to that of NUBEAM and a charge-exchange operator that follows neutrals and allows for multiple re-ionizations. Detailed integrated modelling with the METIS code yields the pressure and current profiles for various sets of achievable engineering parameters. The FIESTA code calculates the equilibrium and a Biot-Savart solver is used to calculate the intensity of the perturbation induced by the TF coils. Initial distributions of the NBI born fast ions are obtained from the newly developed NUR code, based on [S. Suzuki et al. 1998 Plasma Phys. Control. Fusion 40 2097]. We evolve the NBI ions during the complete thermalization process and we calculate the amount of NBI ions loss in the edge region due to neutralizations. Results indicate the NBI losses for various injection geometries, various engineering parameters and various assumptions on the magnitude of the background neutral density. [1] R. Panek et al. Fusion Engineering and Design 123 (2017) 11–1

Modelling of charge-exchange induced NBI losses in the COMPASS Upgrade tokamak

The COMPASS Upgrade tokamak [1] will be a tokamak of major radius R0 = 0.894m with the possibility to reach high field (Bt ~ 5 T) and high current (Ip ~ 2 MA). The machine should see its first plasma in 2023 and H-mode plasma will be obtained from 2025. The main auxiliary heating system used to access H-mode will be 4MW of Neutral Beam Injection (NBI) power. The NBI will have a nominal injection energy of 80 keV, a maximum injection radius Rtan = 0.65m and will create a population of well-confined energetic D ions. In this contribution, our modelling studies the NBI deposition and losses when a significant edge background density of neutrals is assumed. We follow the fast particles in the 3D field generated by the 16 toroidal field (TF) coils using the upgraded EBdyna orbit solver. We have implemented a Coulomb collision operator similar to that of NUBEAM and a charge-exchange operator that follows neutrals and allows for multiple re-ionizations. Detailed integrated modelling with the METIS code yields the pressure and current profiles for various sets of achievable engineering parameters. The FIESTA code calculates the equilibrium and a Biot-Savart solver is used to calculate the intensity of the perturbation induced by the TF coils. Initial distributions of the NBI born fast ions are obtained from the newly developed NUR code, based on [S. Suzuki et al. 1998 Plasma Phys. Control. Fusion 40 2097]. We evolve the NBI ions during the complete thermalization process and we calculate the amount of NBI ions loss in the edge region due to neutralizations. Results indicate the NBI losses for various injection geometries, various engineering parameters and various assumptions on the magnitude of the background neutral density. [1] R. Panek et al. Fusion Engineering and Design 123 (2017) 11–1

Approximations by the Cauchy-type integrals with piecewise linear densities

The paper is a contribution to the complex variable boundary element method, shortly CVBEM. It is focused on Jordan regions having piecewise regular boundaries without cusps. Dini continuous densities whose modulus of continuity ω(·) satisfies limsups↓0ω(s)ln1s=0 are considered on these boundaries. Functions satisfying the Hölder condition of order α, 0 < α ⩾ 1, belong to them. The statement that any Cauchy-type integral with such a density can be uniformly approximated by a Cauchy-type integral whose density is a piecewise linear interpolant of the original one is proved under the assumption that the mesh of the interpolation nodes is sufficiently fine and uniform. This result ensures the existence of approximate CVBEM solutions of some planar boundary value problems, especially of the Dirichlet ones.Web of Science57664062

Global forces on the COMPASS-U wall during plasma disruptions

First, it is shown that during electromagnetic transients in COMPASS-U the poloidal field coils must drain sizeably the current from the vessel and, therefore, reduce disruption forces and their duration. Next, the role of poloidal eddy current (which is absent in some approaches) in the dynamics of vertical and radial forces is found to be essential. Finally, to verify the CarMa0NL modelling for COMPASS-U, the numerical results are cross-validated with general analytical predictions (Pustovitov 2015 Nucl. Fusion 55 113032): the computed vertical force on the tokamak wall is found to be almost zero during rapid ( jump-like) transients, as it should be because of strong skin-effect. This test proves the credibility of the simulation model and computational realization 2021 IAEA, Vienna