Velocity shear, turbulent saturation, and steep plasma gradients in the scrape-off layer of inner-wall limited tokamaks

The narrow power decay-length ($\lambda_q$), recently found in the scrape-off layer (SOL) of inner-wall limited (IWL) discharges in tokamaks, is studied using 3D, flux-driven, global two-fluid turbulence simulations. The formation of the steep plasma profiles measured is found to arise due to radially sheared $\vec{E}\times\vec{B}$ poloidal flows. A complex interaction between sheared flows and outflowing plasma currents regulates the turbulent saturation, determining the transport levels. We quantify the effects of sheared flows, obtaining theoretical estimates in agreement with our non-linear simulations. Analytical calculations suggest that the IWL $\lambda_q$ is roughly equal to the turbulent correlation length.Comment: 5 pages, 5 figure

Electromagnetic turbulence simulations of the tokamak scrape-off layer

We present the newest version of the Global Braginskii Solver (GBS), which addresses tokamak boundary turbulence. GBS now employs a 3D cartesian communicator and a parallel multigrid Poisson/Ampere solver, achieving excellent parallel scalability, and it is being ported to manycore and hybrid architectures. We discuss two new capabilities resulting from improved algorithms: (a) the inclusion of electromagnetic fluctuations at realistic plasma size, and (b) a non-Boussinesq Poisson operator for the electrostatic potential. Simulations of the turbulent plasma dynamics are benchmarked against state-of-the-art imaging diagnostics in tomakak experiments, showing remarkable agreement in many observables

Plasma turbulence in the scrape-off layer of the ISTTOK tokamak

The properties of plasma turbulence in a poloidally limited scrape-off layer (SOL) are addressed, with focus on ISTTOK, a large aspect ratio tokamak with a circular cross section. Theoretical investigations based on the drift-reduced Braginskii equations are carried out through linear calculations and non-linear simulations, in two-and three-dimensional geometries. The linear instabilities driving turbulence and the mechanisms that set the amplitude of turbulence as well as the SOL width are identified. A clear asymmetry is shown to exist between the low-field and the high-field sides of the machine. While the comparison between experimental measurements and simulation results shows good agreement in the far SOL, large intermittent events in the near SOL, detected in the experiments, are not captured by the simulations.United States. Department of Energy (Grant DE-FG02-91ER54109

Global two-fluid simulations of tokamak SOL turbulence

We present non-linear self-consistent global simulations of the SOL plasma dynamics using the Global Braginskii Solver (GBS) code. The code solves on the drift-reduced Braginkii equations, with cold ions. Studied originally for the simulation of the Simple Magnetized Torus (SMT) experiment TORPEX (CRPP, Lausanne), the GBS code has been recently upgraded to describe the SOL turbulence with the introduction of the variable curvature along the magnetic field lines, the magnetic shear, and the electromagnetic effects. The code peculiarity lies in the capability of evolving self-consistently equilibrium and fluctuations as a results of the interplay among the sources, the turbulent transport and the plasma losses at the limiter plates. The non-linear simulations have been interpreted by means of linear analysis of the fluid equations modeling the system. This points out the presence of two main instabilities driving turbulence: the Drift Wave and the Resistive Balloning instabilities. The dependence of the instabilities growth rate and of their properties on the physical parameters of the system, for example the typical length of variation of the plasma density, the safety factor and the magnetic shear have been explained and we identify the regions where each instability dominates

Parque geológico “Costas y sierras del sudeste bonaerense”: identificación, valoración y geoposicionamiento de sitios de interés geológico para un programa de desarrollo local

La conservación del patrimonio geológico de una región es un desafío planteado en las últimas décadas a nivel internacional, para afrontar la amenaza de diversas actividades humanas que pueden provocar un deterioro o la desaparición de la herencia geológica de una región. Con el propósito de conservar el patrimonio geológico, el Instituto de Geología de Costas y del Cuaternario UNMdP-CIC lleva a cabo el proyecto “Parque Geológico Costas y Sierras del Sudeste Bonaerense. Identificación, valoración y geoposicionamiento de sitios de interés geológico para un programa de desarrollo local”, financiado por la CIC. El objetivo del proyecto es conservar el patrimonio geológico del entorno de sierras y costas del sudeste de la provincia de Buenos Aires para las generaciones actuales y futuras. Para lo cual, fue planteado: (1) Delimitar el Parque Geológico en el entorno del corredor costero entre Mar Chiquita y General Alvarado, y del corredor serrano entre Balcarce y Mar del Plata. (2) Identificar, caracterizar y evaluar los potenciales geositios de interés científico, educativo, cultural y recreativo. (3) Valorar los sitios en la zona de estudio escogiendo los lugares más representativos de la geodiversidad que expliquen mejor la evolución geológica del área. (4) Realizar una propuesta de organización y gestión del Parque Geológico. (5) Realizar una propuesta formal para que el Parque Geológico sea declarado Paisaje protegido de interés provincial (Ley 12.704)

Simulation of tokamak SOL turbulence

One of the most important open issue for the realization of a fusion reactor is the understanding of the turbulence that develops at the periphery of the device, in the region called the edge. Turbulence is the major cause of particles and energy losses and it is driven by the presence of plasma and magnetic field inhomogeneities. We present non-linear self-consistent simulations of the edge plasma dynamics and we interpret them by means of linear studies of the fluid equations modeling the system. The linear study points out the dependence of the instabilities growth rate and of their properties on the physical parameters of the system. We identify the regions where each instability dominates. By using the non-linear simulations, we then study how the plasma instabilities non-linearly develop and saturate

Cycling dynamics of the internal kink mode in non-linear two-fluid MHD simulations

The present work describes non-linear simulations leading to a description of diamagnetic thresholds for sawtooth cycles in tokamaks. Provided that a criterion of diamagnetic stabilization for a m/n=1/1 tearing is fulfilled, it is shown that diamagnetic effects alone can drive true sawteeth with complete magnetic reconnection in high temperature Ohmic plasmas with S~10^7-10^

Global two-fluid simulations of tokamak Scape-Off-Layer turbulence

We present non-linear self-consistent 3D global fluid simulations of the SOL plasma dynamics using the Global Braginskii Solver (GBS) code. The code solves the drift-reduced Braginkii equations in a collisional plasma, with cold ions. The GBS code, originally developed for an electrostatic, 2D configuration has been recently upgraded to describe the SOL turbulence with the introduction of the variable curvature along the magnetic field lines, the magnetic shear, and the electromagnetic effects. The code peculiarity lies in the capability of evolving self-consistently equilibrium and 3D fluctuations as a results of the interplay among the sources, the turbulent transport and the plasma losses at the limiter plates. The non-linear simulations have been interpreted by means of linear analysis of the fluid equations modeling the system. This points out the presence of two main instabilities driving turbulence: the Drift Wave and the Resistive Balloning instabilities. The dependence of the instabilities growth rate and of their properties on the physical parameters of the system, for example the characteristic length of the plasma density, the magnetic shear and the beta ratio have been explained and the regions where each instability dominates have been identified