This is the third in a series of related reports on (1) nonstable behavior of widely used ionization gauges, (2) causes of nonstability and nonreproducibility in widely used Bayard–Alpert (BA) gauges, and (3) a stable and reproducible BA gauge design with approximately a tenfold improvement in both stability of gauge calibration after thousands of hours of operation and reproducibility gauge-to-gauge compared to older design BA gauges and inverted magnetron gauges. Computer simulation of electron and ion trajectories utilizing a program named simion was used to optimize the design. A grounded conducting shield of closely controlled dimensions completely surrounds the cathodes and anode. The anode has partial end caps on both ends. Dual, independently tensioned, thoria coated iridium ribbon cathodes are precisely positioned so that the flat emitting surfaces face imaginary axes laterally displaced from the anode axis by a small amount. The cathodes are relatively short compared to the anode. A 0.040 in. diam ion collector and an emission current of 100 μA help extend the upper pressure measuring limit to above 1×10−2 Torr and provide an x-ray limit of 1.6×10−10 Torr. With a 0.005 in. diam ion collector and an emission current of 4 mA, the x-ray limit is 1.4×10−11 Torr and the upper pressure measuring limit is above 1×10−3 Torr. This new technology, called Stabil-Ion technology, provides sufficient stability and reproducibility to justify storing accurate calibration data for a specific Stabil-Ion system or averaged data from a set of nominally identical systems in electronic memory. Thus, the typical nonlinearities in sensitivity and purposeful changes in emission current or gas type do not significantly affect the accuracy of pressure indication. Consequently, accurate real time readout of pressure and stable process control are provided by the new design.

A pulsed probe has been used to measure certain parameters of a time varying plasma in mercury vapor. Langmuir probe characteristics have been obtained by pulsing the probe voltage to successively higher values for μsec intervals at specific times relative to a repetitive discharge pulse. Curves showing the time dependence of the plasma potential, electron temperature, and electron density relative to this pulse are presented. The probe characteristics do not exhibit a sharp break at the plasma potential. This is related to a disturbance of the plasma by the probe. A novel and precise technique for determining the actual plasma potential is described. This technique depends upon the abrupt appearance of a spike on the leading edge of the probe current pulse.

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An all-metal ultra-high vacuum valve is described. The valve has a continuously variable conductance from about 1 l/sec to less than 10−14 l/sec and presumably as small as desired. An equilibrium method of measuring small leakage conductances is described.

Present limitations on attaining low pressures are examined in detail. Evidence for the existence of pumping mechanisms at very low pressures is reviewed and it is shown that the present difficulties in achieving pressures much below 10−12 Torr in room temperature systems appear to be due to inadequate or improper processing of the system materials. Curves showing the partial pressure as a function of time and temperature for volume, surface, dissolved, and permeating gases in a typical system are given. It is concluded on the basis of present evidence that pressures in the 10−16 Torr range should be routinely possible provided the entire system is designed and operated to minimize permeation and is carefully processed to remove dissolved gases.