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. When ECR takes place at the magnetic-well bottom, a potential structure 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 timescale determined by the ion-flow speed. 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. However, this structure is formed only transiently when the ECR point is located in the region of bad magnetic-field curvature. 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.
完全電離無衝突プラズマ流中における電子サイクロトロン共鳴（ECR）点での電位形成を、単純な磁気ミラー配位の磁場配位のもとで調べた。ECRが磁気井戸の底で生じる場合、ECR点周辺の負の電位のくぼみとそれに続く正の電位のピークからなる電位構造が観測される。この電位構造は、イオン流速度によって決まる時間スケールで徐々に崩壊する。収束磁場の場合、ECR点が磁場曲率の良い領域に位置するとき、このような電位構造は定常状態でも持続することが観測される。しかし、ECR点が磁場曲率の悪い領域に位置する場合、この構造は過渡的にのみ形成される。発散磁場中でECRが生じる場合には、磁力線に沿った強い電位降下が現れ、これは磁力線に沿った電子加速に起因し、効果的なイオン加速を伴う。