ANOMALOUS CURRENTS TO A SPHERICAL ELECTROSTATIC PROBE IN A FLAME PLASMA

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 be IMG1 where 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.