Plasma Potential Formation Due to Local ECR

研究了在简单镜面磁场构型下，存在电子回旋共振(ECR)点的全电离无碰撞等离子体流中等离子体势的形成。在单端Q机中产生了磁场势垒、会聚磁场和发散磁场的位形，当ECR发生在磁井底部时，观察到一个由ECR点附近的负电位下降和随后的正电位峰值组成的势能结构。这种势能结构在离子流速度决定的时间尺度内逐渐坍塌，在此期间观察到低频漂移和笛子不稳定性强烈增长。在收敛磁场的情况下，当ECR点位于良好的磁场曲率区域时，观察到这样的势结构保持在稳态。但是，当ECR点位于磁场曲率较差的区域时，这种结构只是瞬时形成的。因此，在简单的磁镜场构型下，ECR点的存在下，离子塞和电子热障势垒的形成不同于串联镜等离子体约束的原始情形。另一方面，当ECR发生在发散磁场中时，沿着场线出现了一个很强的势降，这是场向电子加速的结果，伴随着有效的离子加速。上述势能的形成可以用ECR引起的平行于场线的选择性电子减速/加速以及由于准中性条件而自洽组织的静电离子减速/加速来解释。

Plasma potential formation is investigated in a fully-ionized collisionless plasma flow in the presence of an electron cyclotron resonance (ECR) point under simple mirror configurations of magnetic field. The magnetic-well, converging-field and diverging-field configurations are generated in the single-ended Q machine.When ECR takes place at the magnetic-well bottom, a potential strucature is observed to consist of a negative potential depression around the ECR point and a subsequent positive potential peak. This potential structure gradually collapses in the time scale determined by the ion-flow speed, during which low-frequency drift and flute instabilities are observed to grow intensively. In the case of a converging magnetic field such a potential structure is observed to persist in the steady state when the ECR point is located in the region of good magnetic-field curvature. But, this structure is formed only transiently when the ECR point is located in the region of bad magnetic-field curvature. Thus, the formation of an ion plug and electron thermal-barrier potential is demonstrated in the presence of the ECR point under simple configurations of magnetic mirror field, being different from the original scenario for the tandem-mirror plasma confinement. When ECR takes place in a diverging magnetic field, on the other hand, there appears a strong potential drop along the field lines, which results from a field-aligned electron acceleration, being accompanied by an effective ion acceleration.The potential formations described above are explained by the selective electron-deceleration/acceleration parallel to the field lines due to ECR and electrostatic ion-deceleration/acceleration self-consistently organized due to the condition of quasineutrality.