Speaker
Description
Recent experiments in Heliotron J have delved into the response of energetic-particle-driven MHD
instabilities to electron cyclotron heating and current drive (ECH/ECCD) [1]. Specifically, we
conducted ECH modulation experiments to scrutinize mode stabilization and its underlying physical
mechanisms [2]. In our initial modulation experiment, the NBI power was modest at 90 kW in coinjection, while the second harmonic X mode ECH power was systematically modulated at 50 Hz.
As the ECH power gradually decreased to a certain threshold, it triggered the excitation of an
energetic-particle mode (EPM) with a frequency around 100 kHz [3]. In subsequent experiments,
we elevated the NBI power to approximately 100 kW in co-injection and 450 kW in counterinjection, leading to clearer excitation of the EPM and other modes. Our analysis focused on the
mode excitation's dependence on electron density and ECH power, revealing a time delay in ECH
modulation akin to our previous findings (see Fig. 1), indicating
a nuanced interplay between mode excitation and fast ion
confinement. ECH has the capability to alter ion, electron
Landau damping, radiation damping, and even continuous
spectrum damping. Conversely, variations in Te also impact
electron drag collisions, consequently influencing the
deceleration time. Furthermore, we explored the impact of
magnetic configuration on the mode stability by scanning the
bumpiness (toroidal mirror ripple). We will also compare the
measured mode numbers with results from the STELLGAP and
FAR3d codes.
