Perturbative studies of toroidal momentum transport using neutral beam injection modulation in the Joint European Torus: Experimental results, analysis methodology, and first principles modeling

Abstract

ABSTRACT.Perturbative experiments have been carried out in the JET tokamak in order to identify the diffusive and convective components of toroidal momentum transport. The torque source was modulated either by modulating tangential neutral beam power or by modulating in anti-phase tangential and normal beams to produce a torque perturbation in the absence of a power perturbation. The resulting periodic perturbation in the toroidal rotation velocity was modelled using time dependent transport simulations in order to extract empirical profiles of momentum diffusivity and pinch. Details of the experimental technique, data analysis and modelling are provided. The momentum diffusivity in the core region (0.2<ρ<0.8) was found to be close to the ion heat diffusivity ( χ φ / χ i~0 .7-1.7) and a significant inward momentum convection term, up to 20m/s, was found, leading to an effective momentum diffusivity significantly lower than the ion heat diffusivity (

Core momentum and particle transport studies in the ASDEX Upgrade tokamak

“…However, through the use of modulation techniques it is possible to identify these fluxes separately. This technique has already been used on JET [31,32,33], DIII-D [29], JT-60U [30], and NSTX [27,28] to study momentum transport and has now been developed for AUG following the method used at JET.…”

“…Although our theoretical understanding of momentum transport has developed appreciably [17,18,19,20,21,22,23,24,25,26], validation of momentum theory through comparison to experiment is still in its early stages [27,28,29,30,31,32,33,34,35]. In particular, our understanding of intrinsic momentum fluxes remains largely empirical [36,37,38,39,40,41,42,43] and detailed comparison between theoretically predicted residual stress mechanisms and experimental observations of intrinsic rotation remains an open area of research.…”

Overview of toroidal momentum transport

“…Indeed, quantitative comparisons between experiments and direct numerical simulations are still relatively rare. Quasi-linear modelling efforts have been undertaken [109,124,125] for the diffusivity and the pinch. They show good agreement under some, but not all circumstances.…”

Particle and Momentum Transport in Tokamak Plasmas, the Complicated Path towards the Experimental Validation of the Theoretical Predictions of Transport in Fusion Plasmas

“…A large experimental effort has been dedicated in order to identify the parametric dependences of the experimentally observed convection. The investigations have been carried out with torque modulation experiments, produced by modulation of the NBI power [12,79,80,81,82,101,83,84,85,86], or by means of transients of the toroidal velocity due to a plasma brake induced by the application of nonresonant magnetic perturbations [87,81,88]. More recently, an alternative approach based on the analysis of a large data base of stationary phases of beam heated plasmas at JET has also allowed the identification of the presence of a convective mechanism through an extended statistical analysis, and the main dependences of this convective component have been singled out by means of multivariate regressions [89,90].…”