https://www.febo.com/pipermail/time-nuts/2017-April/104600.html I posted this patent assigned to Frequency Control Corporation on hot wire ionizers at http://gonascent.com/papers/hp/hp5061/US3433944.pdf . They must have been an HP competitor in the 1960s. It discusses the physics of cesium ionization and should be of interest πθ°μΩω±√·Γλ WB0KVV