An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The circuit of the present invention generates clock edges at a minimum of TD seconds apart so long as address transitions do not exceed a pre-determined limit. 95 J\u2266D relative to the cladding diameter J of an optical fiber preform, the cladding diameter J being determined by the diameter and the refractive index of the core of the crude preform.