Lecture

Diffusion and transport in tokamak plasmas

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In course

PHYS-424: Plasma II

This course completes the knowledge in plasma physics that students have acquired in the previous two courses, with a discussion of different applications, in the fields of magnetic confinement and controlled fusion, astrophysical and space plasmas, and so ...

Description

This lecture covers the principles of diffusive transport in tokamak plasmas, including classical and neo-classical diffusion, ambipolar diffusion, and turbulent transport leading to anomalous diffusion. It explains the random walk concept, charge-neutrality effects, and the impact of collisions on diffusive transport. The lecture also delves into the diffusion coefficients, mean squared displacement, and the role of collisions in weakly ionized plasmas. Furthermore, it discusses the fluid model for transport, heat conductivity, and heat exchange between ions and electrons. The presentation concludes with a comparison of classical and neo-classical diffusion, emphasizing the importance of understanding anomalous diffusion and internal transport barriers.

Instructor

Holger Reimerdes

Teaching & PhD PhD Students Martim Zurita, Marta Pedrini, Benjamin Yong Kwak Brown, Pierre Louis Sintre, Massimo Carpita, Richard Alexander David Ducker, Giuseppe Iunior Drago Past EPFL PhD Students Mirko Wensing, Claudia Colandrea, Guang-Yu Sun Past EPFL PhD Students as codirector Gustavo Paganini Canal, Joyeeta Sinha, Roberto Maurizio Courses Control and Operation of Tokamaks PHYS-748 This course treats the main issues in operation and control of a tokamak. Control-oriented models are de

Official source

Related concepts (32)

Diffusion

Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential. It is possible to diffuse "uphill" from a region of lower concentration to a region of higher concentration, like in spinodal decomposition. Diffusion is a stochastic process due to the inherent randomness of the diffusing entity and can be used to model many real-life stochastic scenarios.

Molecular diffusion

Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles. Diffusion explains the net flux of molecules from a region of higher concentration to one of lower concentration. Once the concentrations are equal the molecules continue to move, but since there is no concentration gradient the process of molecular diffusion has ceased and is instead governed by the process of self-diffusion, originating from the random motion of the molecules.

Tokamak

A tokamak (ˈtoʊkəmæk; токамáк) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. , it was the leading candidate for a practical fusion reactor. Tokamaks were initially conceptualized in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov, inspired by a letter by Oleg Lavrentiev. The first working tokamak was attributed to the work of Natan Yavlinsky on the T-1 in 1958.

Plasma (physics)

Plasma () is one of four fundamental states of matter, characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, being mostly associated with stars, including the Sun. Extending to the rarefied intracluster medium and possibly to intergalactic regions, plasma can be artificially generated by heating a neutral gas or subjecting it to a strong electromagnetic field.

Fick's laws of diffusion

Fick's laws of diffusion describe diffusion and were first posited by Adolf Fick in 1855 on the basis of largely experimental results. They can be used to solve for the diffusion coefficient, D. Fick's first law can be used to derive his second law which in turn is identical to the diffusion equation. A diffusion process that obeys Fick's laws is called normal or Fickian diffusion; otherwise, it is called anomalous diffusion or non-Fickian diffusion.

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