Bursting toroidal Alfvén eigenmodes in KSTAR plasmas
PLASMA PHYSICS AND CONTROLLED FUSION(2019)
摘要
We report on observations of bursty mode activity during early neutral beam heating in KSTAR plasmas, before current flat top while the q profile is still evolving. The magnitude of the activity increases with early beam heating, and reduces with the addition of resonant magnetic perturbation magnetic field coils. A mode analysis yields a toroidal mode number of n = 2. The mode is observed to be downward chirping in frequency, and exists for the duration of the slowing-down of the beam. Motional Stark effect constrained equilibrium reconstructions are available at adjacent time slices: we have rescaled the total current to the measured value to obtain the q profile during the mode activity. From this we have computed the mode spectrum and identified a number of candidate gap modes. Wave-particle simulations with plausible distribution functions are computed, which demonstrate that the lowest frequency mode satisfies the condition for wave drive omega(*)/omega > 1, where omega(*) is the fast ion diamagnetic drift frequency. An interesting finding is the change from exponential growth of the mode above n(f) /n(i0) approximate to 0.6, whereby the mode continues to nonlinearly grow at a reduced rate over a period of 100 wave periods up to final saturated amplitude. We believe that this may be because the two spatial resonances at s = 0.4 and s = 0.8 overlap for sufficiently high fast ion density, and so the phase-space volume and fast ion density available to drive the mode increases.
更多查看译文
关键词
Alfven eigenmode,wave particle interaction,nonlinear saturation
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要