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.

Fast-Ion Transport Induced by Alfven Eigenmodes in the ASDEX Upgrade Tokamak 2The temporal evolution of the confined fast-ion profile in the presence of RSAEs and TAEs has been monitored with high spatial and temporal resolution. A large drop in the central fast-ion density due to many RSAEs has been observed as q min passes through an integer. The AE radial and poloidal structures have been obtained with unprecedented details using a fast SXR as well as 1D and 2D ECE radiometers.GOURDON and HAGIS simulations have been performed to identify the orbit topology of the escaping ions and study the transport mechanisms. Both, passing and trapped ions are strongly redistributed by AEs.

Recent experimental and theoretical studies highlight the need to predict the turbulence-induced radial diffusion of energetic particles quantitatively in present-day and future fusion devices. Gyrokinetic simulations with passive fast ion species in realistic tokamak equilibria are used to investigate the influence of the particle energy on diffusion due to electrostatic and electromagnetic turbulence. To facilitate more straightforward comparisons between theory and experiments, scaling relations are derived that allow for writing the relevant diffusivities as functions of experimentally readily accessible quantities. In this context, an improved method for estimating the magnetic fluctuation level is described.

Nonlinear dynamics of single toroidal number gap Alfvén modes destabilised by the the resonant interaction with fast ions is investigated, in Tokamak equilibria, by means of Hamiltonian mapping techniques. The results obtained by two different simulation codes, XHMGC and HAGIS, are considered with reference to n = 2 Beta induced Alfvén Eigenmodes and, respectively n = 6 Toroidal Alfvén Eigenmodes; simulations of the bump-on-tail instability performed by a 1-dimensional code, PIC1DP, are also analysed. A general feature emerges from these results: modes saturate as the resonant-particle distribution function is flattened, because of the fluxes associated to the motion of particles captured in the potential well of the wave, over the whole region where mode-particle power transfer can take place in the linear phase. Such region can be limited by the narrowest of the resonance width and the mode width. In the former case, mode amplitude at saturation exhibits a quadratic scaling with the linear growth rate; in the latter case, a linear growth rate.These findings are explained in terms of the approximate analytic solution of a nonlinear pendulum model. They are also used to prove that the radial width of the single poloidal harmonic sets an upper limit to the radial displacement of passing fast ions produced by a single-toroidal-number gap mode in the large n limit, irrespectively of the possible existence of a large global mode structure formed by many harmonics.