High-Frequency Effect Due to the Axial Drift Velocity of a Plasma Column

The scattering of a plane electromagnetic wave with normal incidence (E field perpendicular to the axis) by a plasma column in the presence of a static magnetic induction ${\mathbf{B}}_0$ has been studied earlier. A heretofore unexplained effect, however, is the existence of a scattered axial field $E_Z$ even when $B_0=0\mathrm{}$. A mechanism responsible for this coupling between the $E_Z$ and the transverse E field, in the absence of $B_0$, is investigated here, namely the role of an axial drift velocity $v_d$. The effect observed is a resonance peak of $E_Z$ occurring at the same density for which there exists a resonance of the scattered transverse E field which is well explained by a uniform cold-plasma model. The same model is therefore assumed here. In this approximation the plasma can be described by a surface charge density $\Sigma$ due to the HF polarization which gives rise to a surface current density $\mathrm{K}=\Sigma {\mathrm{v}}_d$. The boundary conditions then lead to the existence of an $E_Z$ which, for $B_0=0\mathrm{}$, has a $sin\theta$ dependence when the exciting field has a $cos\theta$ dependence. When $B_0\ne 0$, a more complicated theoretical spectrum is obtained. Both the position and the angular dependence of the resonances are in very good agreement with experimental data. The effect predicted by this model is, however, more than an order of magnitude below that observed in a mercury plasma column. This phenomenon can be described as the plasma radio-frequency analog of the static field induced by the Roentgen-Eichenwald current.