The mode transition from a capacitively coupled mode ͑E mode͒ to an inductively coupled mode ͑H mode͒ was observed in an inductive Ar plasma source by applying an axially uniform low B field. The applied fundamental rf was 13.56 MHz and many harmonic components were observed. A beat and standing wave patterns of azimuthally symmetric (mϭ0 mode͒ first and second harmonic pseudosurfaces and helicon waves were measured at various densities (nϳ9.0ϫ10 10 -2.2 ϫ10 11 cm Ϫ3 ) and B fields ͑12-28 G͒. Wave propagation mode changes, from pseudosurface to helicon waves and from helicon to pseudosurface waves, were observed at critical conditions, c / Ͼ3.0 and nϳ2.2ϫ10 11 cm Ϫ3 .

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A new unmagnetized collisional Mach probe theory is developed in order to resolve the collisional effect on Mach probe analysis by including ionization, charge and momentum transfer of ions in the perturbation region of a Mach probe. A fluid model is established by assuming Boltzmann electrons and taking the moments of the one-dimensional Boltzmann transport equation, which contains the two-dimensional transport information as a source, after adding a collisional term. A new relation between the flow velocity and the ratio of the ion sheath current densities is obtained, and is compared with those by a collisionless kinetic theory and a particle-in-cell simulation in the applicable range of these theories. A new relation between flow velocity and the ratio of the ion sheath current densities shows that ion–neutral collisions have a very strong effect to produce much smaller Mach numbers from the same ratio than those by collisionless models.

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