Enhancement of the Plasma Potential by Fluctuating Electric Fields near the Ion Cyclotron Frequency

It is found that ion cyclotron resonance frequency can create an ion-plugging plasma potential equal to several times $\frac{T_e}{e}\left(\simeq \frac{T_i}{e}\right)$ in the Phaedrus tandem mirror end cells or at the end of the central cell. A model based on a local balance of electron expulsion by the rf field ${\tilde{E}}_z$ and trapping by Coulomb scattering predicts the magnitude and scaling of the potential with density and rf antenna current. This model is in reasonable agreement with experimental observations. This ion-cyclotron resonance-frequency enhanced potential increases as the plasma density decreases and as the antenna current increases.