ABSTRACT
The purpose of this study is to understand the effect of the shape of crosssection of the tube on the plasma parameters, when the tube’s dimension is smaller than the cutoff value. Although Chapters 4 and 5 deal with tubes of different geometry (near-circular and rectangular), the desired information cannot be obtained because these tubes have different nature of magnetic fields (multicups and nonmulticusp), and their area of cross-sections are different. In the current experiment, tubes of a square and a near-circular crosssection have been designed where both have multicusp magnetic fields, are of the same lengths, and have almost the same cross-sectional areas, so that the microwave power density in the tubes can be kept the same. This allows us to compare the efficiency of wave absorption depending upon the inner geometry of the tube. Moreover, in a four-sided geometry, a square waveguide is helpful because in a square cross-section one can construct the same number of magnetic poles on each side. This way the symmetry and
uniformity of the magnetic field is improved. The results of the comparative study are presented, and possible mechanisms of the plasma maintenance and the effect of the cross-sectional shapes of the tubes are discussed.
