Theory of electrostatic probes in a low-density flowing continuum plasma: numerical solutions for a sphere stagnation point

An exact numerical method has been used to study a probe stagnation point in a continuum flowing plasma. The solutions for the 'low-density continuum' plasma, i.e. with mean free path much less than probe radius much less than Debye length, are calculated for Reynolds numbers Re from 0 to 400, charged diffusion Reynolds numbers Rasub(c) from 0 to 10, and scaled probe potentials phisub(p)/epsilon from 0 to +- 32, where phisub(p) = eVsub(p)/kTe, epsilon = T/Te. The numerical results show that (i) the usual semi-log method for temperature determination leads to large errors; (ii) the effect of flow leads to large errors in the space potential determination; (iii) for a sufficiently large accelerating potential, the currents always show a linear dependence; (iv) approximate current expressions are suggested at smaller Reynolds numbers (Re much less than 0.1) and diffusion Reynolds numbers (Rasub(c) less than or equal to 1). (author)