中文摘要：

为了探求HT-7托卡马克装置中加低杂波后等离子体约束改善这一现象的原因，文章从电子的径向力平衡方程人手，通过数值模拟程序计算出欧姆阶段和低杂波阶段下的径向电场分布。结果发现，加低杂波后，在低杂波功率沉积的地方，径向电场在负方向变强，径向电场分布梯度变陡，加波前后径向电场的差值（△E）分布形成了凹槽结构，意味着加波后的径向电场剪切加强；通过与HTH7托卡马克中等离子体约束改善的实验现象比较，发现低杂波电流驱动阶段内部输运垒（ITB）产生的区域与径向电场分布的凹槽区域相一致，结果说明低杂波引起的径向电场的变化可能是导致加波后约束改善的原因。

英文摘要：

In order to understand the physical mechanism of the improvement of plasma confinement by the lower hybrid current drive（LHCD） in HT-7 tokamak, it is necessary to study the effect of LHCD on radial electric field profile. Based on the electron＇s radial force equilibrium, the profiles of Er in ohmic（OH） and LHCD phases are calculated by using a simulation code. The main results are given as follows, after the onset of lower hybrid wave（LHW）, Er becomes more negative near the position of LHW power depositiom and the gradient of Er profile becomes steeper, and a notch structure is gen- erated by the change of Er profile after the LHCD（z~Er）, demonstrating the enhanced Er shear in the LHCD phase. By comparing the calculated results with the experimental results, it is found that the region of internal transport barrier（ITB） in LHCD phase is accordant with that of the notch of Er profile. The results indicate that the changes of Er by LHCD are the possible reasons leading to the improvement of plasma confinement after injecting LHW.