Analysis of the heating scenarios of the ion Bernstein wave (IBW) experiment in Frascati Tokamak Upgrade

Abstract

Ion Bernstein waves (IBWs) have been proposed as useful for heating and improving transport in tokamak plasmas. The experiments carried out so far have not provided a sufficient assessment of this concept, due to the occurrence of parasitic phenomena that caused poor reproducibility of IBW heating and confinement effects. An experiment on FTU has given the first test of IBW coupling to a tokamak plasma by a waveguide antenna utilized in place of the standard dipole antenna. In addition, the experiment operates at a high frequency that is expected to reduce the non-linear wave-plasma interaction at the edge. These phenomena were considered to be the cause of the lack of RF power penetration in the plasma bulk and of the production of impurity influx. The possible IBW experimental scenarios expected for the FTU plasma are described. To perform this analysis, quasi-linear and non-linear models are utilized for the wave propagation, damping and turbulence suppression suitable for transport barrier formation. As a result of this study, FTU is expected to be a useful facility for testing the IBW concept for advanced tokamaks.

Nonlinear ICRF-plasma interactions

“…47 These types of calculations can also take into account convection of wave energy out of the interaction region in inhomogeneous plasmas. In FTU it was shown 48 that there are competing constraints on the optimal SOL density: high to reduce PDI, but low to reduce reflected power for good linear coupling.…”

“…[58][59][60] This knowledge has stimulated theoretical work on the calculation of rf driven flows, beginning with the pioneering work of Craddock and Diamond 61 and continuing up to the present. 48,[62][63][64][65][66][67][68][69] A number of 1-D and ray tracing calculations established that local absorption of IBW power at a cyclotron resonance was accompanied by redistribution of momentum that resulted in sheared poloidal (bipolar) flows.…”

Ion-Scale Sideband Waves and Filament Formation: Alfvénic Impact on Heliospheric Plasma Turbulence

“…The Bernstein mode can be both electrostatic and electromagnetic, and is particularly suited for transferring the fluctuation energy toward higher frequencies by three-wave couplings [37]. The ion Bernstein mode is extensively studied in Tokamak, fusion, and laboratory plasmas [38][39][40][41][42]. Several observational studies indicate the ion Bernstein mode in the solar wind [43,44].…”

Chapter 2: Highlights of the Physics Studies in the FTU

“…41,42 The radio-frequency~rf ! power is directly coupled to the plasma electrons, through Landau damping, and to the thermal ions near the resonant layer by ion-cyclotron damping.…”

“…A careful comparison between discharge with IBW and discharges with impurity gas injection led to the conclusion that the peaking of the pressure profile was due to the IBW wave. 42 The electron thermal diffusivity profile was estimated by the JETTO code, using as an input the experimental electron temperature and density profiles, the equilibrium configuration, the radiation profile, and the effective ion charge. Deposition profile expected from the linear theory and neoclassical resistivity were assumed.…”