Measurement of neoclassically predicted edge current density at ASDEX Upgrade

Abstract

Abstract. Experimental confirmation of neoclassically predicted edge current density in an ELMy H-mode plasma is presented. Current density analysis using the CLISTE equilibrium code is outlined and the rationale for accuracy of the reconstructions is explained. Sample profiles and time traces from analysis of data at ASDEX Upgrade are presented. A high time resolution is possible due to the use of an ELM-synchronisation technique. Additionally, the flux surface averaged current density is calculated using a neoclassical approach. Results from these two separate methods are then compared and are found to validate the theoretical formula. Finally, several discharges are compared as part of a fuelling study, showing that the size and width of the edge current density peak at the low field side can be explained by the electron density and temperature drives and their respective collisionality modifications.

Electromagnetic turbulent structures: A ubiquitous feature of the edge region of toroidal plasma configurations

“…This suggests that electromagnetic filaments could be responsible also for bending magnetic field lines 10 , local modification of magnetic topology 12 or wider modification of the plasma column as suggested for example in the case of ASDEX-Upgrade. Here it has been found that the ELMs are associated with a reduction of the plasma radius hinting to a movement of the plasma outside the last close flux surface and to a redistribution of the edge current profile 13 . In the present paper we focus in particular on the direct measurement of turbulent filamentary structures current density, which can provide an efficient channel for current transport 14 .…”

Analysis of temperature and density pedestal gradients in AUG, DIII-D and JET

“…6 (b) it is useful to study the bootstrap current. With larger col-lisionality the bootstrap drive coefficients decrease [30]. However, this does not necessarily mean smaller bootstrap contribution to the edge current density.…”

“…In contrary, j boot can even increase slightly. Following the ideas in [30], a simple estimate can be made. Assuming constant pressure and proportionality between gradients and pedestal height, a change of the collisionality from 0.5 to 1.7 will influence the bootstrap current by less than 5%.…”

ELM behaviour and linear MHD stability of edge ECRH heated ASDEX Upgrade plasmas

“…However, the strong edge variation of the pressure gradient and current density peak are only poorly reflected. Constraining the edge pressure profile leads to a much higher accuracy in the final equilibrium [12]. This requires high quality kinetic measurements, which at AUG are provided by electron cyclotron emission (ECE) [13], Thomson scattering [14,15], lithiumbeam emission spectroscopy [16,17], deuterium cyanide interferometry [18] and charge exchange recombination spectroscopy [19] diagnostics.…”