FORCE-FREE PLASMA CURRENTS DRIVEN BY ELECTROMAGNETIC OSCILLATIONS WITH E-PARALLEL-TO-B

A special superposition of oppositely propagating circularly polarized monochromatic plane waves defines a stationary electromagnetic oscillation in a cavity, with E parallel to B. Inside a plasma, this type of oscillation induces an ac current J that is parallel to the magnetic field B, and is hence force free. In the low-frequency limit, a transient dc plasma current is driven by the special oscillation field. It is shown that these oscillations cannot interact with an externally imposed field B0, so that they exist only if J parallel-to B parallel-to B0.