Filamentary velocity scaling validation in the TCV tokamak

Abstract

A large database of reciprocating probe data from the edge plasma of TCV (Tokamak à Configuration Variable) is used to test the radial velocity scalings of filaments from analytical theory [J. R. Myra, D. A. Russell, and D. A. D'Ippolito, Phys. Plasmas 13, 112502 (2006)]. The measured velocities are mainly scattered between zero and a maximum velocity which varies as a function of size and collisionality in agreement with the analytical scalings. The scatter is consistent with mechanisms that tend to slow the velocity of individual filaments. While the radial velocities were mainly clustered between 0.5 and 2 km/s, a minority reached outward velocities as high as 5km/s or inward velocities as high as-4km/s. Inward moving filaments are only observed in regions of high poloidal velocity shear in discharges with Bx∇B away from the X-point, a new finding. The filaments have diameters clustered between 3 and 11mm, and normalized sizes â clustered between 0.3 and 1.1, such that most filaments populate the resistive-ballooning regime, therefore, most filaments in TCV have radial velocities with little or no dependence on collisionality. Improvements in crosscorrelation techniques and conditional averaging techniques are discussed which reduce the sizes determined for the largest filaments, including those larger than the scrape-off layer (SOL).

Blob velocity scaling in diverted tokamaks: A comparison between theory and simulation

“…The charge separation leads to an electric field and its associated E Â B drift that causes the blob to move radially outwards. This basic mechanism of radial motion is confirmed by a series of blob studies conducted on the TORPEX device, 18,19 by experiments in limited and diverted plasmas on TCV, 20 and by numerical simulations of seeded blobs (see, e.g., Refs. [21][22][23][24].…”

Nitrogen-seeded divertor detachment in TCV L-mode plasmas

“…(middle) Evolution of the outer midplane SOL density profile during a ne -ramp. The profiles are taken with the RCP [43,44] at different times during well-reproducible discharges. The density profiles as a function of the distance to the separatrix.…”

Understanding the turbulent mechanisms setting the density decay length in the tokamak scrape-off layer

“…x ρ 2 s ρ 2 * L 2 n b /(n a 2 y )] 1/5 and the factor 0.5, obtained by comparing the scaling with the simulation results, accounting for the fact that our estimate is an upper limit that neglects various mechanisms slowing the blobs (Tsui et al 2018).…”

“…This is due to the existence of blobs -high density structures elongated along the magnetic field lines that propagate outwards due to their associated electric field (D 'Ippolito, Myra & Zweben 2011). The properties of blobs have been measured extensively in tokamaks (Walkden et al 2016;Zweben et al 2016;Tsui et al 2018), stellarators (Sánchez et al 2003), reversed field pinches (Spolaore et al 2004) and basic plasma experiments (Antar et al 2001;Carter 2006;Furno et al 2008a), however, the generation of blobs and prediction of blob-mediated transport remain open questions.…”