A statistical approach to investigate plasma dynamics in gyrokinetic simulations of stellarator turbulence

Turbulent dynamics in stellarator plasmas is investigated by a geometrical method. Gyrokinetic simulations of ITG mode driven turbulence in the core-region of the stellarator W7-X, with realistic quasiisodynamic topologies using the GENE software are considered. The turbulent states are approximated by probability distribution functions where distances between thermodynamic states can be computed according the thermodynamic length methodology which allows the use of a Riemannian metric on the phase space. The geometric methodology is suitable in order to understand stochastic processes involved in e.g. order-disorder transition, where a sudden increase in distance is expected. In gyrokinetic plasma turbulence simulations avalanches, e.g. of heat and particles, are often found and in this work this novel method for detection is investigated. Previously [1,2] 1D versions have been investigated however this falls short in identification of coherent modes. The Hurst exponent, the Information Length and the Dynamic Time is computed from the 2D time series. Based on these measures the transport features of large scale modes can be investigated, identified by a sudden increase in information.