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Density peaking phenomena have been studied in different magnetic field configurations in a low field (< 100 Gauss) helicon discharge. The study has been carried out in the linear helicon plasma device (Barada et. al., Rev. Sci. Instrum. 83, 063501, 2012) using argon gas with m = +1 right helical antenna operating at 13.56 MHz by varying the magnetic field from 0 Gauss to 100 Gauss (G) with two different magnetic field geometry. The plasma density varies with varying the magnetic field at constant input power and gas pressure and reaches to its peak value at a critical magnetic field value (s). For a magnetic field of 88 G near the antenna the density rises at an axial location away from the antenna in the diffusion chamber having a diverging magnetic field. On the m=-1 propagation side of the antenna, the density peak vanishes around 30 G which is well evident on the m=+1 propagation side. The results are explained on the basis of resonance cone propagation of right circularly polarized helicon waves and the vanishing of density peak at 30 G along with observation of density peak at 5 G and 12 G at z=-18 cm (m=-1) propagation side are explained with polarization reversal mechanism of electromagnetic waves. [ABSTRACT FROM AUTHOR]

Experiments on the Madison Symmetric Torus (MST), a reversed field pinch operating at the University of Wisconsin-Madison, have observed blackbody levels of emission in the electron cyclotron range of frequencies (ECRF) with ω[sub pe] ∼ 3ω[sub ce]. We speculate the emission is a result of electrostatic electron Bernstein waves (EBW) emitted from the core and mode converted into the electromagnetic waves at the plasma edge. A 16 channel absolutely calibrated radiometer simultaneously measures the radiation spectrum for frequencies between 4 GHz and 8 GHz. Comparison of the measured radiation temperature with profiles measured by Thomson scattering indicates that the mode conversion efficiency can be as high as ∼ 75%. Emission is preferentially in the X-mode polarization, and is strongly dependent upon the density and magnetic field profiles at the mode conversion point. These results have been used to study: (1) the diagnostics potentiality of EBW emission for electron temperatue measurement and (2) the feasibility of heating and current drive in overdensed RFP plasma through the perpendicular launch of X-mode in the ECRF. [ABSTRACT FROM AUTHOR]