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www.thinkSRS.com 1 Hot vs. Cold Ionization Gauges Every modern high vacuum and ultrahigh vacuum system relies on some form of ionization gauge for pressure measurements under 10-3 Torr. There are currently two competing ionization gauge technologies to choose from - the hot cathode gauge (HCG) and the cold cathode gauge (CCG). This application note is designed to help vacuum users choose between the two competing ionization technologies. Each gauge type has its own advantages and disadvantages. The best choice requires careful consideration of the operating characteristics of both gauges and is dependent on the application. In This Application Note Introduction 3 Hot-Cathode Gauges (HCG) 4 Cold-Cathode Gauges (CCG) 6 Conclusions 8 (408)744-9040 Stanford Research Systems www.thinkSRS.com 2 Hot vs. Cold Ionization Gauges Stanford Research Systems (408)744-9040 www.thinkSRS.com Hot vs. Cold Ionization Gauges 3 Introduction Every modern high vacuum and ultrahigh vacuum system relies on some form of ionization gauge for pressure measurements under 10-3 Torr. There are currently two competing ionization gauge technologies to choose from which are viable means for pressure measurements between 10-2 and 10-10 Torr: 1. In the hot cathode gauge (HCG) ionizing electrons from a thermionic cathode are accelerated by suitable electrodes into an ionizing space. 2. In the cold cathode gauge (CCG) ionization is caused by a circulating electron plasma trapped in crossed electric and magnetic fields. In both cases, the electrical current resulting from the collection of the positive ions created inside the gauge is used as an indirect measure of gas density and pressure. This application note is designed to help vacuum users choose between the two competing ionization technologies. Each gauge type has its own advantages and disadvantages. The best choice requires careful consideration of the operating characteristics of both gauges and is dependent on the application. For more detailed information on this subject consult the following publications: 1. J. M. Lafferty, Ed., "Foundations of Vacuum Science and Technology", p. 414, section 6.9., John Wiley and Sons, NY, 1998. Note: This is an excellent book recommended for any high vacuum question. 2. R. N. Peacock, N. T. Preacock, and D. S. Hauschulz, "Comparison of hot cathode and cold cathode ionization gauges", J