Edge Physics Forum 2017

Edge Physics Forum

Influence of external magnetic perturbations on the plasma boundary in L-mode and on the plasma position control system of ASDEX Upgrade

[mehr]

Edge Physics Forum

Inter-ELM pedestal evolution in AUG - Impact of the triangularity on the pedestal structure and dynamics

[mehr]

Edge Physics Forum

Neutrals in the tokamak edge: neoclassical ions and momentum transport

Due to their high cross-field mobility, neutral particles interacting with the plasma through charge-exchange can contribute to the radial transport of toroidal angular momentum even at low relative densities. The contribution of non-Maxwellian parts of the ion distribution function is particularly interesting, as it can generate a momentum flux through the neutrals even in the absence of rotation. The neutrals can therefore contribute to intrinsic rotation. We model neutrals using a short mean-free-path approximation, in a background of neoclassical ions having arbitrary collisionality, on closed flux surfaces near the edge. As an application, we will show the effect of flux surface geometry on plasma rotation in 'predictive' mode where the neutrals are assumed to dominate the angular momentum transport. We will also show the momentum flux through neutrals in 'interpretive' mode, where plasma profiles from an L-mode AUG discharge are used to estimate the magnitude of the angular momentum flux through neutrals, finding that it may be a significant fraction of the angular momentum input from NBI. [mehr]

Edge Physics Forum

Investigation of the influence of the ion heat flux on access to regimes of improved energy confinement in Alcator C-Mod.

The role of the edge ion heat flux for transitions from L-mode to H-mode in Alcator C-Mod is investigated. Several selected discharges from the low to medium density range in C-Mod were analyzed by time dependent power balance analysis using the transport code TRANSP. The ion heat flux was calculated by adding the power from the ion cyclotron resonance heating deposited in the ion channel and the electron-ion heat exchange. These calculations showed that the surface integrated edge ion heat flux obtained just prior to the L-H transition increases linearly with line average density, which agrees with previous results from AUG. It appears, as if a critical amount of heat flux per particle is necessary for the transition. The comparison of the results of this work and previous research at AUG lead to a simple linear scaling law for the critical edge ion heat flux necessary for the transition into H-mode. [mehr]

Edge Physics Forum

Dependence of Tokamak Confinement on ELM Power Losses

[mehr]

 
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