SOL transport in TCV

Radial profiles of parallel SOL ion flows at several poloidal locations in the outer midplane vicinity have been measured in SNL and SNU equilibria. Matched ohmic density scans for both toroidal field directions yield co-current directed flows which decrease as density increases and reverse direction with field inversion. Excellent agreement is found between experiment and a simple analytic expression for the neoclassical Pfirsch-Schlueter ion flow. At any given density, the mean value of the flows obtained above or below the plasma midplane for both field directions reveals a field independent component. This offset increases with density, is directed away from the midplane and is absent on the midplane, indicating a ballooning type origin. It can be clearly identified with the time average of transient over-pressure generated in field aligned filaments driven by interchange motions. These 'blobs' increase in number with density and are observed more frequently with decreasing plasma current. This is consistent with an increase in fluctuations and turbulence driven radial transport with increasing collisionality and is evidently related to the blob formation process. During ELM activity filaments are observed in IR images of the outer divertor target, consistent with energy release in the outer midplane region from a number of discrete toroidal locations. They are also seen by Langmuir probes in the SOL and at the outboard midplane walls. For Type III ELMs, radial velocities are in the range ∼ 1 km/s. On average, between 5-8 substructures are detected at the wall in each ELM (Type III and Type I ELMs) and the fluctuating parallel particle flux statistics during the filaments appear very similar to those of the inter-ELM phases. Tomographic reconstructions of the radiation distribution during ELMs on the ∼ 5 micros timescale clearly show that a disturbance occurs in the X-point region before any particle flux reaches first wall surfaces. Most of the ELM energy reaching the targets does so in the separatrix vicinity, with the integral energy deposited up to the peak energy deposition normalised to total deposited energy at the outer target in the range 0.2-0.3 for Type III ELMs and 0.3-0.4 for Type I ELMs. modelling of the ELM parallel transport is progressing favourably, both using the 2D edge code package SOLPS5 and the 1D particle-in-cell kinetic code BIT1. (author)