Three experiments are described about the measurement of pressures over the range from 10
-7 to 10
-11 Torr or lower. That is, (1) the pressure measurements by the Bayard-Alpert gauge, (2) the dependence of the discharge current in the getter ion pump on pressure, and (3) the decreasing characteristics, of the emission current with pressure and time in the field emission diode.
In the range of 10
-11 Torr, the pressure error measurement by B-A gauge is considerably laige due to the X-ray effect and the instability. The discharge current is proportional to the power from one to three halves of pressure. Also, the decreasing time of the emission current is inversely proportional, to the pressure, approximately. From results of the experiment (2) and (3), the pressure of 10
-11 Torr or lower is presumed to be obtained.
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