This paper reports on two-dimensional measurements of plasma parameters and magnetic eigenmode profiles in capacitive, inductive and helicon wave sustained discharge modes of a helicon source with high spatial resolution. It is demonstrated that plasma densities ranging over four orders of magnitude can be achieved. The plasma profiles of the capacitive and inductive discharges are completely consistent with the accepted discharge models. The magnetic eigenmode structure in the helicon mode shows great differences in the mode number and axial wavelength compared to the capacitively coupled discharge. In particular, multiple reflections of the obliquely propagating helicon wave fronts at the plasma boundaries are observed in the helicon wave sustained plasma. Moreover, the consistent connection of plasma parameters with discharge parameters via the helicon wave dispersion is demonstrated with varying magnetic field and for various discharge power levels.

Observations in space and laboratory plasmas suggest magnetic reconnection as a mechanism for ion heating and formation of non-Maxwellian ion velocity distribution functions (IVDF). Laser-induced fluorescence measurements of the IVDF parallel to the X line of a periodically driven reconnection experiment are presented. A time-resolved analysis yields the evolution of the IVDF within a reconnection cycle. It is shown that reconnection causes a strong increase of the ion temperature, where the strongest increase is found at the maximum reconnection rate. Monte Carlo simulations demonstrate that ion heating is a consequence of the in-plane electric field that forms around the X line in response to reconnection.

Detailed Langmuir probe measurements of the plasma density, plasma potential, and electron temperature in the cylindrical helicon device VINETA [C. M. Franck et al., Phys. Plasmas 9(8), 2002] are presented. The probe measurements cover the entire radial-axial plane including the helicon antenna region. Two magnetic field configurations are compared: homogeneous magnetic field in the helicon antenna region and magnetic field gradient at the transition between the antenna and the discharge chamber. It is demonstrated that the converging magnetic field leads to the formation of steep plasma density and potential increase, which is strongly correlated with the position of the maximum field gradient. No electron heating detached from the helicon source is observed. The measurements strongly suggest that the plasma profiles are the direct result of volume reduction due to magnetic field convergence, which leads to the formation of a single sheath-like layer in front of the helicon source.

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