Plasma boundary phenomena in tokamaks

Abstract

Effects of the plasma boundary can have a substantial influence on the behaviour of the entire plasma in tokamaks. Progress in the field, particularly that over the last decade, is reviewed, with emphasis on experimental observation. Simple modelling for interpretation is also included.

Impurity transport in the divertor of the Alcator C-Mod tokamak

“…Other factors may however over-ride the simple picture. Reverse flow in the scrape-off layer (SOL), as observed in 2-D fluid calculations [1], is one possibility and the ion temperature gradient force acting away from the target plate is another.…”

Mapping the intrinsic stochasticity of tokamak divertor configuration

“…field line length spectrum collapsing into a less bristly declining pattern once the open surface region, the scrape off layer (SOL) [1] has been reached where the mostly parallel transport of particles and energy to the target takes place.…”

“…Poloidal ergodic divertors constitute a prime technique in the management of impurities [1], magnetohydrodynamic (MHD) stabilization [2] and high performance mode inducement [3] for present day and future tokamaks. In particular, the challenge posed by the heat flux impact on the vessel target inner surfaces has been considerably averted by means of divertor dissipative techniques [4].…”

“…These evolve to a rich and complex homoclinic topology [5] on which the patterns of deposition on the target depend. It has been long known that magnetic field lines follow the trajectories of a 1 1 2 degree of freedom Hamiltonian [6] and where parallel conductivity largely outweighs transversal diffusion, so that plasma flows preferentially along the magnetic field lines. Therefore, the inherent use of area preserving maps to model the system has turned out to be an often revealing as well as processing-time saving practice since as early as the 1950's [7,8].…”

Momentum Exchange of a Plasma with its Surroundings

“…Plasma momentum has been interested in fusion oriented devices and, for an example, plasma flow in a scrape-off layer is linked to tokamak confinement [1]. The plasma momentum has also attracted researchers' attention in other applied fields, such as electric propulsions [2] and plasma actuators [3].…”