Speaker
Francesco Napoli
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1064.pdf
Non-monochromatic RF power injection to control lower hybrid
parametric instabilities in tokamak plasmas
F. Napoli1, C. Castaldo1, A. Cardinali1, S. Ceccuzzi1, R. Cesario1, G. Ravera1, A. Tuccillo1,
B. J. Ding2, M.H.Li2
1
ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044
Frascati (Roma), Italy
2
Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, PR China
In present day LHCD experiments, parametric instabilities must be controlled for the
accessibility of the driver pump to the inner layers of a tokamak plasma [1]. Previous works
already studied, theoretically [2] and experimentally [3], the parametric interaction of a
non-monochromatic pump driver with plasmas in the lower hybrid range of frequencies. The
purpose of such studies was to find experimental conditions useful to mitigate, or better
suppress, the parametric instabilities. However, if we consider the technical feasibility of the
pump modulation, no practical conclusions could be drawn since stabilization effects on
parametric instabilities can be achieved only if the frequency bandwidth of the modulated
driver pump is larger than the resonance width of the parametric instability. Unfortunately,
this condition is seriously limited by the frequency bandwidth of available power sources.
This work presents a new nonlinear parametric dispersion relation for an amplitude
modulated pump driver. This equation is based on an accurate nonlinear kinetic model of
lower hybrid wave propagation, useful to analyse the instabilities emerging in the outer
layers of a tokamak plasma [4,5]. We first validate numerical solutions of the new parametric
dispersion relation reproducing the experimental observations of lower hybrid amplitude
modulated pump experiments [3]. Furthermore, by changing the driver pump coherence, we
study how undesirable parametric effects can be significantly reduced in the SOL plasma for
EAST and FTU tokamaks. As a breakthrough of this study, we find a new amplitude
modulation scheme exploitable within the frequency bandwidth of microwave power sources
available for lower hybrid experiments.
[1] R. Cesario, et al., Nature Comms, 1 55 (2010)
[2] V. Stefan, Phys. Fluids, 26 1789 (1983)
[3] K. Matsumoto, et al., Plasma Phys., 25 1441 (1983)
[4] F. Napoli, et al., Plasma Phys. Contr. Fusion, 55 095004 (2013)
[5] F. Napoli, C. Castaldo, 44th EPS Conf. on Plasma Phys. (2017)
