On the orbital motion limited theory for a small body at floating potential in a Maxwellian plasma

The condition for the validity of the orbital motion limited (OML) theory i s reviewed, with reference to the calculation of the floating potential att ained by a spherical body immersed in a plasma. It is shown that the OML th eory is never satisfied in Maxwellian plasmas, even in the case of very sma ll bodies, i.e. those with radii much smaller than the plasma Debye length. The case considered is that where the ion temperature is less than or equa l to the electron temperature. The results are relevant to the theory of du sty plasmas, where the OML theory has been much employed.