In DIII-D, it has been observed that ELM frequency decreases by 40% and ELM spacing becomes more regular in time when heating is changed from pure neutral beam injection (NBI) to predominantly electron cyclotron heating (ECH) in ITER similar shape plasmas. In comparison with the pure NBI discharges, pedestal fluctuations in magnetics and density increase in the ECH-dominated discharges. Recovery of the pedestal profiles like electron density (ne), temperature (Te) and pressure (pe) shows marked differences for these two heating schemes. Average profiles in the last 30% of the ELM cycle show higher Te, lower ne, and similar pe at the pedestal top for the ECH discharge when compared to the NBI discharge. The gradient of Te (∇Te) is also steeper at the pedestal in the ECH discharge. Magnetic fluctuations show three distinct modes at 13–116 kHz in the ECH discharges only. ne fluctuations show two modes evolving in the inter-ELM period of the ECH discharge, a low-frequency (400 kHz) quasi-coherent mode (LFQC) and high-frequency (∼2 MHz) broadband (HFB) fluctuations. Evolution of these modes has marked correspondence with the inter-ELM ∇Te recovery. A sharp decrease in the Dα baseline is observed whenever the LFQC weakens and the HFB grows, prior to each large ELM. Transport coefficients obtained from TRANSP show that MTM and/or TEM are plausible candidates for the observed fluctuations. Linear gyrofluid simulation (TGLF) corroborates this characterization. TGLF shows that the linear growth rate of the most dominant mode peaks at ion-scale (kθρs ∼ 0.4) at the pedestal steep gradient and the frequency is in the electron diamagnetic direction. It is proposed that increased fluctuations in the ECH-dominated case, due to increased ∇Te, caused an increase in fluctuation-driven transport in the pedestal and slowed the pedestal recovery between ELMs, leading to a reduction in the ELM frequency.
在DIII-D中，观察到当加热从纯中性束注入（NBI）改为以电子回旋加热（ECH）为主时，在ITER相似形状等离子体中，ELM频率降低40%，且ELM时间间隔变得更加规则。与纯NBI放电相比，在ECH为主的放电中，台基的磁涨落和密度涨落增加。台基轮廓（如电子密度ne、温度Te和压力pe）的恢复在这两种加热方案下表现出显著差异。在ELM周期的后30%平均时段内，ECH放电的台基顶部具有更高的Te、相似的ne和pe。ECH放电中台基处的∇Te也更陡。磁涨落仅在ECH放电中显示出三个不同的模式，频率在13–116 kHz范围内。密度涨落显示出两个模式，在ECH放电的ELM间期演化：一个低频准相干模（LFQC，约400 kHz）和一个高频宽带模（HFB，约2 MHz）。这些模式的演化与ELM间期∇Te的恢复有对应关系。每当LFQC减弱且HFB增强时，Dα基线出现急剧下降，随后发生下一次大ELM。从TRANSP获得的输运系数表明，磁化漂移模（MTM）和/或俘获电子模（TEM）是观测到的涨落的可能候选机制。线性回旋动理学模拟（TGLF）证实了这一特征：在台基陡峭梯度区域，最不稳定模式的线性增长率在离子尺度（kθρs ∼ 0.4）达到峰值，且其频率位于电子抗磁方向。由此提出，在ECH为主的放电中，由于∇Te增大导致涨落增强，进而引起台基中涨落驱动的输运增加，减缓了ELM间期台基的恢复，最终导致ELM频率降低。