In the 2018 EAST experimental campaign, a very high central electron heating, fully-non-inductive discharge with the core electron temperature over 9 keV has been achieved. Such high central electron heating was realized by injecting radio frequency waves, including 1.8 MW lower hybrid wave (LHW) and 0.8 MW electron–cyclotron waves (ECW). Experimental diagnosis indicates two different time scales characterizing the electron heating process, a rapid and a slow rise of the central electron temperature after the injection of ECW. In this work, integrated modeling is performed to investigate the physical mechanisms of such high electron heating. Five characteristic phases during the increase of the electron temperature are chosen for modeling. In phase 1, the electron heating is by LHW alone. The modeling confirms that the LHW can only sustain the core electron temperature Te ≈ 5.5 keV, which is consistent with the experiment. In phase 2, the electron temperature increases rapidly after the first 0.4 MW ECW is injected. The result shows that the rapid increase of the electron temperature is due to the interaction between the ECW and the electrons. With the increase of the electron temperature, the electron flux induced by the trapped electron modes (TEMs) and the electron temperature gradient driven modes (ETGs) is enhanced in the core region. In phase 3, the electron temperature increases slowly after phase 2. It is found that the slow increase is mainly due to the flattening of the density profile. The flattening of the density profile can decrease the thermal diffusivity of the electrons mainly induced by the TEMs leading to a higher electron temperature for a given heating source. In phase 4, the electron temperature again increases rapidly after the second 0.4 MW ECW is injected. The physical mechanism is similar to that in phase 2. In phase 5, the LHW power deposition of the LHW remains almost unchanged compared to that in phase 4 since the electron temperature is sufficiently high. The slow rise of the electron temperature is caused by the improvement of the electron energy confinement as thermal diffusivity of the electrons is decreased due to the flattening of the electron density profile, which is similar to the main reason in phase 3.
2018年EAST实验活动中，实现了中心电子温度超过9 keV的非常高中心电子加热、完全无感应放电。这种高中心电子加热是通过注入射频波实现的，包括1.8 MW低杂波（LHW）和0.8 MW电子回旋波（ECW）。实验诊断表明，在注入ECW后，中心电子温度的上升存在两个不同的时间尺度，即快速上升和缓慢上升。在本工作中，进行了集成建模以研究这种高电子加热的物理机制。在电子温度上升过程中选取了五个特征阶段进行建模。在第一阶段，电子加热仅由LHW提供。建模证实，LHW只能维持中心电子温度Te ≈ 5.5 keV，这与实验一致。在第二阶段，注入第一束0.4 MW ECW后，电子温度迅速上升。结果表明，电子温度的快速上升是由于ECW与电子之间的相互作用。随着电子温度的升高，芯部区域由俘获电子模（TEMs）和电子温度梯度模（ETGs）引起的电子通量增强。在第三阶段，第二阶段之后电子温度缓慢上升。研究发现，缓慢上升主要是由于密度分布的平坦化。密度分布的平坦化可以降低主要由TEMs引起的电子热扩散系数，从而在给定加热源下获得更高的电子温度。在第四阶段，注入第二束0.4 MW ECW后，电子温度再次快速上升。其物理机制与第二阶段类似。在第五阶段，由于电子温度足够高，LHW的功率沉积与第四阶段相比几乎保持不变。电子温度的缓慢上升是由于密度分布平坦化导致电子热扩散系数降低，从而改善了电子能量约束，这与第三阶段的主要原因类似。