Turbulent Particle Transport in Magnetized Plasmas (original) (raw)
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It is shown that electron transport due to a generic low-frequency electrostatic turbulence in tokamak geometry results in the relaxation to a peaked, self-sustained plasma density profile no(r), rather than to a diffusion-induced Oat distribution. The relaxed density profile depends on the magnetic geometry and the distribution of turbulence. The associated inward pinch velocity V, = DV lnno results from the competition of the turbulent diffusion of trapped electrons over the poloidal magnetic flux coordinate P and the collisional relaxation toward a Maxwellian distribution function.
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2020
Overview Turbulent pinch and diffusion of impurities in tokamak plasmas Impurity transport in magnetically confined plasma is one of the important problems in fusion research. This process is not completely understood and it represents a very active research field. We have found a new type of pinch, the ratchet pinch The ratchet pinch induced by the gradient of the magnetic field in turbulent plasma was developed from a fundamental idea toward a complex realistic model that can be used for specific tokamak plasma studies. The milestone for 2009 is the development of the model by including the mass-charge effects. The conditions for peaked density profiles were analyzed. The mass-charge dependence of the pinch velocity and of the diffusion coefficient was analyzed. A code that determines these transport coefficients for given impurity ions in a turbulence with realistic characteristics was developed. The pinch velocity was shown to be important only in the nonlinear stage of the turb...
Plasma edge transport with magnetic islands—a comparison between tokamak and reversed-field pinch
Nuclear Fusion, 2014
In the reversed-field pinch (RFP) edge, measured transport and flows are strongly influenced by magnetic islands (Vianello 2013 Nucl. Fusion 53 073025). In fact, these islands determine a differential radial diffusion of electrons and ions which, interacting with the wall, give rise to a characteristic edge ambipolar potential. Such island structures also arise in tokamak plasmas, when resonant magnetic perturbations (RMPs) are applied for control of edge-localized modes. They impose a characteristic modulation to edge electron density and temperature fields, in close correlation with the local magnetic vacuum topology (Schmitz 2012 Nucl. Fusion 52 054001). In order to develop a generic picture of particle transport with magnetic islands located in the plasma edge between RFPs and tokamaks with RMP, test-particle transport simulations are done on TEXTOR with the same tool used in RFX-mod, namely, the guiding-centre code ORBIT (White and Chance 1984 Phys. Fluids 27 2455-67). A typical TEXTOR discharge in the (m, n) = (12, 4) configuration is reconstructed and analysed with ORBIT. We use Poincaré and connection length analysis of electrons and ion orbits to analyse the magnetic structure taking into account the different gyro-orbits of both constituents. Density distributions of test ions and electrons are calculated and used to obtain an initial estimate of the plasma potential and radial electric field around the island.