Non-linear study of fast particle excitation of Alfvén eigenmodes during ICRH

Abstract

High-power ion–cyclotron resonance heating (ICRH) can produce centrally peaked fast ion distributions with wide non-standard drift orbits exciting Alfvén eigenmodes (AEs). The dynamics of the AE excitation depends not only on the anisotropy and the peaking of the fast ion distribution but also on the decorrelation of the AE interactions and the renewal of the fast ions resonant with the AE by ion–cyclotron interactions. A method of self-consistently including the evolution of the distribution function of fast ions during excitation of AEs and ICRH has been developed and implemented in the SELFO code. Numerical simulations of the AE dynamics and ICRH give a variation of the AE amplitude consistent with the experimentally observed splitting of the mode frequency. The experimentally observed fast damping of the mode as the ICRH is switched off is also evident in the simulations.

Recent experimental results and modeling of RF heating of ([sup 3]He)-D JET plasmas: RF as a tool to study transport

“…Gamma rays [16] with energies in the range ≈ 10 − 18MeV testify for 3 He being RF heated and the reaction D + 3 He → 5 Li + γ(16.4MeV ) taking place. Significantly reducing the RF power during intervals of a few hundred ms allows to identify the effect of the RF heating on the MHD activity: modes disappear or become much weaker when the RF heating level is reduced, in good agreement with expectation from theory predicting such modes rely on fast particle "current sources" for their excitation [17]. The threshold reaction 12 C(p, p γ) 12 C reaction, producing 4.4MeV γ rays requires high energy protons.…”

Nonlinear dynamics of phase space zonal structures and energetic particle physics in fusion plasmas

“…Using equation (19), equation (14) can be cast as On the RHS, the dominant contribution in the nonlinear dynamics of EP PSZS is fluctuation-induced resonant particle scattering. In equation (20), however, the contribution of other collisional [71] and noncollisional [107][108][109][110] scattering processes could be readily included by corresponding scattering operators. Collisioninduced scattering, introduced in [71], was the first type to be considered; however, micro-turbulence-induced diffusion has been demonstrated to be more relevant in typical ITER conditions [109,110].…”

“…Collisioninduced scattering, introduced in [71], was the first type to be considered; however, micro-turbulence-induced diffusion has been demonstrated to be more relevant in typical ITER conditions [109,110]. Radio-frequencywave-induced scattering [107] has also been shown to dominate over collisional scattering in conditions of practical interest in present-day experiments [108]. These additional physics affect the nonlinear evolution of F 0EP via self-consistent interplay of SAW/DAW and nonperturbative EP responses on typical time scales longer than those considered here, τ γ ∼ − NL L 1 ; and, thus, they will be neglected.…”

Theory on excitations of drift Alfvén waves by energetic particles. I. Variational formulation

“…26,27 Radiofrequency wave induced scattering 24 has also been shown to dominate over collisional scattering in conditions of practical interest in present day experiments. 25 For increasing EP drive, when nonlinear EP displacement becomes a significant fraction of the perpendicular fluctuation wavelength, the same pressure curvature coupling term with dg is responsible for the onset of non-adiabatic dynamics of phase space zonal structures, 2,54,60,61 d F 0EP , due to the self-consistent interplay of mode structures and EP transports 47 (cf. further discussions in Sec.…”

“…1, 14,20 Thus, EPs may act as mediators of cross-scale couplings in burning plasmas, 21,22 and a clear understanding of spatial and temporal scales involved with the interactions of DAWs and EPs is crucial. It is, furthermore, also necessary to carry out self-consistent treatment of both nonlinear wave-wave and wave-particle interactions, 1,2 including resonant EP collisional 23 and non-collisional [24][25][26][27] scattering. In fact, these are the "two possible nonlinear routes" that produce the features of SAW/DAW "turbulent spectrum and assess the associated heating/acceleration and transports."…”