中心专家来访--Dr. Vinicius Duarte[2017-06-14]

First Talk:

Time: Thursday, June 15th, 3:00 pm

Venue: Rm. 413, Bld. 11#, Yuquan Campus

Title about: Quasilinear relaxation formalism for energetic particle interaction with Alfvénic modes

Speaker: Dr. Vinicius Duarte, Univ. of Sao Paulo, Brazil

Abstract :
Reduced kinetic models can be effective tools to address the transport of fast ions in tokamaks. In particular, we propose a resonance-broadened quasilinear diffusive framework in which the relevant variables are chosen to be the invariants of the unperturbed resonant particle Hamiltonian. The formulation describes the distribution function evolution in phase space and captures both regimes of isolated and overlapping modes. We show how linear perturbative MHD codes can be used to provide information such as eigenstructures, resonance surfaces and mode-particle interaction matrix elements, all of which are necessary for realistic modeling of experimental discharges. Preliminary numerical results are discussed, as well as the prospects of using the resonance-broadened quasilinear model for whole-device simulation through proper interfacing with global transport codes.

Second Talk:

Time: Tuesday, June 20th, 10:00 am

Venue: Rm. 413, Bld. 11#, Yuquan Campus

Title about: Prediction of nonlinear evolution character of energetic-particle-driven instabilities

Speaker: Dr. Vinicius Duarte, Univ. of Sao Paulo, Brazil

Abstract :
Energetic-particle-driven instabilities can seriously limit the performance of present-day and next-generation fusion devices. We propose a criterion for the likely nature of losses of fast ions in tokamaks to be in the convective or diffusive nonlinear regimes. The criterion, which is shown to be rather sensitive to collisional and micro-turbulent processes, ultimately translates into a condition for the applicability of quasilinear modeling for realistic tokamak eigenmodes scenarios. The criterion is tested and validated against NSTX and DIII-D, where the chirping mode behavior is shown to be in accord with the model. It has been found that the anomalous fast ion transport is a likely mediator of the transition between the fixed-frequency mode behavior and rapid chirping in tokamaks. In addition, micro-turbulence appears to resolve the disparity with respect to the ubiquitous chirping observation in spherical tokamaks and its rarer occurrence in conventional tokamaks.