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Experimental results for the ion current to a cylindrical electrode in a flowing continuum plasma are compared with the currents calculated from a convection-dependent thin-sheath theory obtained by extending the theory of Lam to cover convection rather than diffusion-generated currents. The relation derived with this theoryIi≈5.3ε01/4e3/4μi1/4rp1/4vf3/4ne3/4V1/2l,  (mks)where ε0 is the permittivity of free space, e is the electronic charge, μi is the ion mobility, rp is the probe radius, vf is the plasma/probe velocity, ne is the ionization density, V is the probe bias, and l is the probe length, is found, on the average, to predict the experimental currents to within ±30% over ranges of 0.1–5 mm in probe radius, 5×102−4×103 cm/sec in probe/plasma velocity, 5×1016−2×1018/m3 ionization density, and 10–100 V in probe bias. Further support for a convection-dependent thin-sheath model is provided by two experimental observations: (1) The current is observed to vary as V1/2 as predicted by the convection-dependent theory rather than to saturate as would be expected of a diffusion-generated current. (2) Separate measurements reveal a marked asymmetry in the current distribution around the probe surface as expected in a thin-sheath situation.

It is shown that the blast wave from a pulsed linear arc inherently leaves flows in its wake which propagate as a cylindrical version of a conventional hyrdodynamic 'puff'. These flows are generated by the transition of the initially cylindrical shock wave to an ultimate spherical configuration. Schlieren cinematography of the expanding flows yields results which are in good agreement with a theory based on a single blast wave model of wake flow formation. The results both support a previous hypothesis of Chomiak (1979) on the subject of spark ignition and establish a mechanism which accounts for the observed increase in the rate of combustion when short duration sparks are used.

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By following the same line of reasoning which the authors used in a previous paper, concerned with cylindrical probes, the ion current Ii to a spherical probe (radius rp, bias voltage V) immersed in a collision-dominated flowing plasma of subsonic velocity vf has been calculated to beIMG1where ne is the electron density, μi the ion mobility, e the electronic charge and ϵ0 the permittivity of free space. This theory is only valid for conditions where the plasma sheath diameter r0>>rp.A propane-air flame with a moving probe was used to investigate the above relationship. Reasonable agreement (considering the approximations made in deriving the theoretical relationship) was obtained between measured and theoretical ion currents.