An Oscillator Model for rf-Discharge Lamps Used in Atomic Clocks: The rf-Discharge as a Complex Permeability Medium

In the rf-discharge lamp of an atomic clock, the inductor of a Colpitts or Hartley oscillator surrounds a glass bulb containing a vapor of Rb and a noble gas typically Xe or Kr. Rf-energy is extracted from the field leading to ionization of the Rb, and in recombination with electrons these Rb ions produce the resonant light necessary for atomic signal generation. From an electrical perspective, the discharge can be viewed as a permeable medium located inside an inductors coils. This permeable medium, however, must have both a real and an imaginary part not only does the discharge alter the phase of the circuits rf-field, it also extracts energy from the resonant circuit. Here, we consider the manner in which this complex permeability enters the electrical description of the oscillator, and its likely dependence on discharge parameters.