Experiments on Parametric Instability of Lower Hybrid Mode

Lower Hybrid Experiments on MST

Current drive using RF waves has been proposed as a means to reduce the tearing fluctuations responsible for anomalous energy transport in the RFP. A traveling wave antenna operating at 800 MHz is being used to launch lower hybrid waves into MST to assess the feasibility of this approach. Parameter studies show that edge density is a major factor in antenna/plasma coupling. Gas puffing near the...

Electromagnetic particle simulation of the linear mode conversion and the nonlinear parametric decay instability of lower hybrid waves in tokamaks

In plasma simulations where the speed of light times a characteristic length is at a much higher frequency than the relevant parameters in the system, such as the plasma frequency, implicit methods begin to play an important role in generating e cient solutions in these multi-scale problems. Under conditions of scale separation, one can rescale Maxwell’s equations in such a way as to give a mag...

Characterization of onset of parametric decay instability of lower hybrid waves

The goal of the lower hybrid current drive (LHCD) program on Alcator C-Mod is to develop and optimize ITERrelevant steady-state plasmas by controlling the current density profile. Using a 4x16 waveguide array, over 1 MW of LH power at 4.6 GHz has been successfully coupled to the plasmas. However, current drive efficiency precipitously drops as the line averaged density (ne) increases above 1020...

Resonant Parametric Excitation in Lower-hybrid Heating of Tokamak Plasma*

Modulational instability of lower hybrid waves at the magnetopause

The role of lower hybrid waves at the magnetopause is reexamined. It is found that for the maximum observed wave power, the lower hybrid waves are unstable to a modulational instability on the magnetosheath side of the magnetopause. The modulational instability leads to localized field structures , oriented predominantly along the magnetic field. Such patchy lower hybrid turbulence has been obs...