Abstract Photoionization of Io's neutral hydrogen ring combined with cross- L diffusion by flux-tube interchange is shown to be a possible source and transport mechanism for the inner low-energy plasma regime discovered by Pioneer 10. The diffusion coefficient calculated from the number density profile inferred from the Pioneer 10 data is consistent with that required to supply the energy for the synchrotron radiation by the same diffusion process. The proposed mechanism is supported by showing that alternative loss mechanisms to balance the photoion production rate are improbable. Because of the equatorial confinement of the ions and the corotational energy that they acquire, both intrinsic features of the Io source, the proposed mechanism is shown to be free of serious difficulties associated with a Jovian ionosphere source for the inner plasma regime. With Io as the source for the inner plasma regime, the main objection is removed for interpreting the outer plasma regime in terms of the predicted plasmasphere of Ioannidis and Brice.