Experimentally corroborated model of pressure relaxation limit cycle oscillations in the vicinity of the transition to high confinement in tokamaks

Abstract

An analytical formula systematically predicts the observed frequency of pressure relaxation limit cycle oscillations in the vicinity of the transition to high confinement in four tokamaks (JET, ASDEX Upgrade, COMPASS, Globus-M). The experimental dataset spans the widest available range of frequencies, machine sizes and plasma ion species. The machine size dependence is explained by the connection length scale of plasma flows parallel to the magnetic field. The model also explains the observed up-down poloidal current asymmetry and the impact of the plasma ion species mass and charge.

Experimental characterization of the quasi-coherent mode in EDA H-Mode and QCE scenarios at ASDEX Upgrade

“…The errors of the linear fit are calculated as the standard deviation of the maximum and the minimum possible slope, including the errors of the experimental data. Equation ( 2) is similar to the results of Birkenmeier et al [38] (f LCO ∼ 1/β e ) and Grover [39] (f LCO ∼ 1/ √ β e ) for Limit Cycle Oscillations (LCO) in I-phase plasmas. The latter model bases on a predator-prey-like coupling between the in-out asymmetry in the pressure and an up-down asymmetric flow perturbation, i.e.…”

“…The latter model bases on a predator-prey-like coupling between the in-out asymmetry in the pressure and an up-down asymmetric flow perturbation, i.e. the Stringer spin up mechanism [40] might play a major role (see [39]).…”