Transport barrier in 5D gyrokinetic flux-driven simulations

International audienceAbstract Two ways for producing a transport barrier through strong shear of the E × B poloidal flow have been investigated using GYSELA gyrokinetic simulations in a flux-driven regime. The first one uses an external poloidal momentum (i.e. vorticity) source that locally polarizes the plasma, and the second one enforces a locally steep density profile that also stabilizes the ion temperature gradient (ITG) instability modes linearly. Both cases show a very low local turbulent heat diffusivity coefficient χ T turb and a slight increase in core pressure when a threshold of ω E × B ≈ γ ¯ lin (respectively the E × B shear rate and average linear growth rate of ITG) is reached, validating previous numerical results. This pressure increase and χ T turb quench are the signs of a transport barrier formation. This behaviour is the result of a reduced turbulence intensity which strongly correlates with the shearing of turbulent structures as evidenced by a reduction of the auto-correlation length of potential fluctuations as well as an intensity reduction of the k θ spectrum. Moreover, a small shift towards smaller poloidal wavenumber is observed in the vorticity source region which could be linked to a tilt of the turbulent structures in the poloidal direction

Impurity transport through two types of transport barrier in 5D gyrokinetic simulations

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Lixiviação de nitrogênio em latossolo incubado com lodo de esgoto Nitrogen leaching in a latosol incubated with sewage sludges

Lodo de esgoto contém teores elevados de N orgânico. Se for aplicado em quantidade excessiva em solos, há risco de poluição de águas subsuperficiais com nitrato, produto da mineralização do N. Por essa razão, um dos critérios agronômicos para a determinação da taxa máxima de aplicação do lodo de esgoto é a quantidade de N mineral que será disponibilizada às culturas. Neste trabalho, são apresentados os resultados relativos à lixiviação de N mineralizado em um Latossolo Vermelho distroférrico incubado durante 224 dias com dois tipos de lodo de esgoto anaeróbios, um de origem urbana (Franca, SP) e outro com presença de despejos industriais (Barueri, SP). Cada lodo de esgoto foi aplicado em quatro doses, contendo 0,13, 0,3, 0,5 e 1,0 g kg-1 de N orgânico. Essa quantidade de substrato mineralizável foi equivalente a 5, 11, 22 e 43 t ha-1 de lodo de Franca, e a 8, 15, 31 e 61 t ha-1 de lodo de Barueri. O experimento foi conduzido em colunas de percolação, sob temperatura de 25 a 28 °C em laboratório, fazendo-se lixiviações com solução extratora de KCl 0,01 mol L-1. Foram determinadas as quantidades de N mineral (N-NH4+ e N-NO3- + N-NO2-) extraídas nos percolados em doze épocas. Houve correlação significativa entre as quantidades aplicadas de N na forma orgânica e as quantidades de N mineralizadas durante a incubação nos dois tipos de lodo avaliados. O potencial de mineralização estimado pelo modelo exponencial simples foi de 73 mg kg-1 de N no solo sem aplicação de lodo, e aumentou de 107 para 224 mg kg-1 e de 132 para 364 mg kg-1 nos tratamentos com o lodo de esgoto de Franca e de Barueri, respectivamente. A fração de mineralização potencial do N orgânico dos dois tipos de lodo de esgoto decresceu com o aumento das doses aplicadas: 26, 25, 21 e 14 % para o de Franca, e 43, 39, 34 e 27 % para o de Barueri. Em consequência, o potencial de lixiviação de N no Latossolo aumentou de 46 para 207 % com as doses do lodo de Franca, e de 81 para 399 % com as doses do lodo de Barueri.<br>Sewage sludges contain high levels of organic N. If these residues are applied in excess to soils, there is the risk of polluting the groundwater with nitrate, a product of N mineralization. For this reason, one of the criteria underlying the determination of the maximum N application rate to soils is the crop available N. This paper presents the results of a 224 day laboratory leaching study on organic N mineralization of anaerobically-digested sewage sludges from two treatment plants, namely Franca (urban sludge) and Barueri (urban-industrial sludge), both located in São Paulo State, Brazil. The sewage sludges were applied to 0-0.20 m Latosol (Oxisol) samples at four rates, containing 0.13, 0.3, 0.5 and 1.0 g kg-1 of organic N; these treatments were equivalent to the soil application of 5, 11, 22 and 43 t ha-1 of Franca sewage sludge and to 8, 15, 31 and 61 t ha-1 of Barueri sewage sludge. The soil samples with treatments were incubated in percolation tubes at temperatures between 25 and 28 °C. The tubes were periodically leached (12 times) with 0.01 mol L-1 KCl, and N-NH4+ and N-(NO3- + NO2-) were determined in the leachates. During the incubation, there was a significant correlation between the rate of organic N applied as sludges and the net inorganic N accumulation in the leachates, for both sludges. The potential N mineralization estimated by the single exponential model for the soil without sludge was 73 mg kg-1 of N, and increased from 107 to 224 mg kg-1 and from 132 to 364 mg kg-1 in the Franca and Barueri-treated soils, respectively. The potential mineralization fraction of organic N in the residues decreased with increasing rates: 26, 25, 21 and 14 % for the Franca, and 43, 39, 34 and 27 % for Barueri sewage sludge. Thus, the potential for N leaching in the studied Oxisol increased from 46 to 207 % when increasing doses of Franca sewage sludge were applied, and from 81 to 399 % under increasing doses of Barueri sludge