Nonlinear energetic particle transport in the presence of multiple Alfvénic waves in ITER

Abstract

This work presents the results of a multi mode ITER study on Toroidal Alfvén Eigenmodes, using the nonlinear hybrid HAGIS-LIGKA model. It is found that main conclusions from earlier studies of ASDEX Upgrade discharges can be transferred to the ITER scenario: global, nonlinear effects are crucial for the evolution of the multi mode scenario. This work focuses on the ITER 15 MA baseline scenario with with a safety factor at the magnetic axis of q 0 = 0.986. The least damped eigenmodes of the system are identified with the gyrokinetic, non-perturbative LIGKA solver, concerning mode structure, frequency and damping. Taking into account all weakly damped modes that can be identified linearly, nonlinear simulations with HAGIS reveal strong multi mode behavior: while in some parameter range, quasi-linear estimates turn out to be reasonable approximations for the nonlinearly relaxed energetic particle profile, under certain conditions low-n TAE branches can be excited. As a consequence, not only grow amplitudes of all modes to (up to orders of magnitude) higher values compared to the single mode cases but also, strong redistribution is triggered in the outer radial area between ρ pol = 0.6 and 0.85, far above quasi-linear estimates.

Nonlinear interplay of Alfvén instabilities and energetic particles in tokamaks

“…One possible application of this result is helping defining the regime of applicability of models which aim at studying the nonlinear wave-particle interaction of Alfvén modes with a prescribed, fixed mode structure (see for example Ref. [31,32]). A dedicated investigation of this regime of applicability, with particular interest at realistic tokamak scenarios, will be done in a dedicated paper.…”

Saturation of Alfvén modes in tokamak plasmas investigated by Hamiltonian mapping techniques

“…Intermediate regimes have been examined by numerical simulation studies [21][22][23][24]. Several points have been evidenced.…”

Reanalysis of the beam-plasma instability using the Dyson-like equation formalism

“…(20), by assigning the self-consistent field evolved from Eqs. (15). The results are shown in Fig.7 0.00090 0.00095 0.00100 0.00105 0.00110 0.00115 0.00120 0.00125 0.00130 and have to be compared with respect to Fig.4.…”

“…(Color online) Evolution of the distribution function evaluated from the numerical simulation of the fully self-consistent N -body system Eqs (15),. for the selected case M = 1, r = 912 and η = 0.0035 (same asFig.3).…”

“…(Color online) Evolution of the distribution profile from the numerical integration of Eqs (20),. with assigned selfconsistent mode generated byEq (15)…”