Structure in the Edge Plasma Profiles in Tokamaks

Abstract

It is argued that the structure observed in radial profiles in the tokamak edge plasma is determined by the requirements of ion particle, momentum and energy conservation and the underlying transport mechanisms in the presence of sources and losses of particles, energy and momentum. The intent of this paper is to define a systematic formalism that can be employed for evaluating these transport coefficients from experimental inference and comparison with theory. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Recent Developments in Plasma Edge Theory

“…5 Radial electric field [7] Combining the summed multiple ion and electron momentum balance equations using an interspecies friction term of the form…”

“…(12) provides an insight into how the radial electric field (and hence the quantities such as ion orbit loss, radial ion flux and rotation that depend upon it) might be controlled by creating a poloidal or toroidal current in the plasma, most likely in the edge plasma. It should be possible to pull all of the foregoing together into self-consistent "first-principles" calculations for the radial particle flux, rotation velocities and radial electric field [7]. The particle sources, ion-orbit-and X-loss, and radial diffusive and non-diffusive (electromagnetic pinch, X-transport) transport processes and the return currents necessary to maintain charge neutrality should determine the radial particle flux.…”

Extensions of ion orbit loss theory

“…The most general is the loss of ions on passing or banana-trapped orbits that leave the plasma by drifting outward across the last closed flux surface (as developed, e.g., in Refs. 7 and 13-15 or [18][19][20][21][22]. Both thermalized plasma ions and energetic neutral beam ions (and fusion alpha particles) can be lost in this manner.…”

“…We have recently developed a model [18][19][20][21][22] for (i) the calculation of the radially cumulative fractions of ion particles F orb , momentum M orb , and energy E orb in a tokamak plasma flowing outward across an internal flux surface that are on drift orbits that would carry them immediately outward across the last closed flux surface (i.e., be ion orbit lost) and (ii) for the calculation of how these ion orbit losses reduce the corresponding radial particle C, momentum M, and energy Q fluxes that would be calculated in the absence of ion orbit loss from the respective radial particle (continuity), momentum and energy balance equationsĈ…”

Evolution of edge pedestal transport between edge-localized modes in DIII-D

“…This ion orbit loss (IOL) reduces the particles, energy, and momentum in the plasma; a return current of ions from the scrape-off layer (SOL) is required to balance the charge loss 27 and maintain macroscopic plasma neutrality. Both the ion orbit loss and the return current are taken into account using a numerical model, 28,29 which calculates the minimum energy required for a particle at a given location and with a given velocity to access a possible loss orbit and escape confinement.…”