ABSTRACT
In Chapter 5, we have seen that a plasma could be produced in a near-circular multicusp waveguide with a dimension smaller than the cutoff value. In a waveguide with a multicusp magnetic field, the field lines are arched along the circumference connecting poles of opposite polarity, as shown schematically in Figure 6.1a. On the other hand, the electric field of the circular mode (TE11) is peaked at the center and curved radially outward as shown in Figure 6.1b. Therefore, when waves are launched into a circular multicusp waveguide, the electromagnetic coupling gives rise to locations inside the waveguide where the electric field can be perpendicular or parallel to the static magnetic field (ordinary (E ‖ B)) and extraordinary E ⊥ B modes. It is of interest to make an independent study of the dependence of the plasma parameters and the power absorption in these two principal modes. This will help us to understand the plasma production and maintenance mechanisms in a multicusp waveguide with regard to the effectiveness of the wave modes.
