John J. Sullivan

Development of variable capacitance pressure transducers for vacuum applications

The development of variable capacitance diaphragm‐type pressure transducer systems for vacuum applications is described in detail. This technology area is an interesting and challenging problem of design and manufacturing engineering and incorporates an interdisciplinary mixture of material science, and state‐of‐the‐art techniques in electronics. Since the measurement system must be usable for a wide variety of applications in vacuum science ranging from very high accuracy metrology transfer standards to general‐purpose vacuum measurements under very demanding environmental conditions, many conflicting factors must be considered in the design. For all practical purposes, this technology has evolved over a 35 yr period from 1949 to 1984 within which there have been several distinct developmental time periods; 1949–1969, 1970–1975, 1975–1980, 1981–1984. This paper will review the technology, considering the chronological development of sensors, signal conditioners, and overall transducer systems. Some very ...

Mass Spectrometric Sampling of Glow Discharges

Continuous mass spectrometric sampling of the transient behavior of various gas species from a dc glow discharge originally filled with CO2, and mixtures of CO2-H2, (pressure range 50–1000 μ, discharge current 50–200 mA) have been studied by means of a specially constructed mass spectrometer (90° magnetic deflection) gas-sampling system. The sampling technique employed differential pumping of the mass spectrometer by a constricted ion-getter pump using a variable entrance aperture (valve) to the sampling system. The response of the system to time-varying concentrations is derived and the realization of optimum conditions discussed. This work is part of a program to investigate the gaseous electronics aspect of sealed CO2 laser operation.

Precision molecular flow measurement and control for single and multigas systems

This paper presents recent advances in precision molecular flow measurement and control for single backfill gases as well as describing the important factors to be considered in multigas flow and ratio control of several gases at pressures above 0.0133 Pa. A comprehensive theoretical analysis is given describing the variables to be considered in practical systems. Theoretical and experimental data are presented on a new design of molecular flow element specifically designed for vacuum flow applications of any gas, including corrosive types. Single and multigas measurement and control applications using the new flow element with electronic manometer measurement and control instrumentation include reactive sputtering, reactive ion etching, and plasma reactor deposition and etching systems.

Analysis and optimization of closed loop vacuum control systems

A detailed theoretical study of vacuum control systems operating below and in the transition region is presented. System performance of a servo controlled metal−sealed valve and capacitance manometer transducer system is analyzed by means of computer solutions of the nonlinear equations governing its performance. Characterization and optimization of various types of systems are discussed. System volume, throughput, and pumping system characteristics as well as the nature of the control valve are shown to be of prime consideration for control accuracy and step response.

PRESSURE BURSTS IN BAKEABLE ULTRA-HIGH VACUUM VALVES DURING OPENING AND CLOSING.

Abstract : The pressure increase delta p produced by opening and closing bakeable ultrahigh vacuum valves of different commercial sources has been determined using mass spectrometric and other standard techniques. Typical results show: (1) Dependence of delta p on geometry and material of bellow seat and gasket and their previous treatment. (2) Delta p (Bellows; gasket closing, opening) approaches after initial operation a constant value. (3) Delta p (closing) < Delta p (opening for the gasket). (4) Delta p (closing) same order of magnitude as Delta p (opening for the bellows). (5) Pressure bursts correspond in most cases to an equivalent increase of the partial pressure of H2. (6) Delta p (bellows) shows weak dependence on background pressure, delta p (gasket) is pressure independent. Results are applied to a mass spectrometric sampling method. It is shown that the introduction of bakeable valves into the system may be the limiting factor of the experiment, and otherwise ideal conditions will permit measurement of impurity ratios, e.g. for H2 in He in the order of 1/10 to the 7th power at best. (Author)

Hydrogen Impurity Removal from Closed Noble-Gas Discharge Systems

The removal of hydrogen, considered as an impurity gas, from a closed, noble-gas (helium) discharge system is studied using the techniques of (1) hydrogen pumping through a heated palladium membrane and (2) hydrogen gettering by a titanium film deposited on a water-cooled stainless steel surface. Mass spectrometric and optical measurements are presented which show the effect of helium background (pressure range 10−9 to 10−1 Torr) on hydrogen-removal rate. Experimental results of hydrogen gettering on titanium agree with theory, and not only support, but extend earlier work of other investigators. Removal of hydrogen by the palladium membrane is about equally effective for the geometry employed. In addition, the dependence of deposition rate and film thickness of titanium on helium background pressure and source temperature are discussed.

Removal of hydrogen impurities in closed noble gas discharge systems

Abstract : The removal of hydrogen, considered as an impurity gas, from a closed noble gas (helium) discharge system is studied using the techniques of (1) hydrogen pumping through a heated palladium membrane and (2) hydrogen gettering by a titanium film deposited on a water-cooled stainless-steel surface. Mass spectrometric and optical measurements are presented which show the effect of helium background on hydrogen removal rate. Experimental results of hydrogen gettering on titanium agree with theoretical calculations based on kinetic theory, and not only support, but extend earlier work of other investigators. Removal of hydrogen by the palladium membrane is about equally effective for the geometry employed. In addition, laser transmission measurements of deposition of titanium films on a glass surface are studied. Dependence of deposition rate and film thickness on helium background pressure, and source temperature are shown. (Author)