Ultra-High Vacuum Use of Bayard-Alpert Ionization Gauges

Comparisons are made between the collected ion current vs electron emission current for a ``nude'' gauge (Veeco BGT-75) and a glass enclosed gauge (Veeco RG-75) both of the Bayard-Alpert type. The ion current is directly proportional to the electron current for the nude gauge, when the electron current is 100 μA or less, down to ion currents as low as the x-ray limit of the gauge which is 3×10−10 Torr. Good agreement between the glass and nude gauges is obtained over the limited range of electron currents where the glass gauge exhibits proportional behavior. A getter-ion pumped ultra-high vacuum system was used for the experiments.