Ti Sublimation Pumps

    In a titanium sublimation pump, an electrical current passes through a rod or wire of titanium and heats it until its surface temperature rises enough to slowly sublime the metal. The resulting film of titanium covering all surfaces within a line-of-sight to the filament, reacts with the active gas molecules striking them to form nonvolatile compounds. In this context, nitrogen, oxygen, hydrogen, etc. become active gasses, reacting with the titanium film. After depositing the initial film, the current decreases below sublimation level. When all the film has reacted, the current increases again, either manually or by timer/pressure control, to deposit another film. Thus, the Ti sub pump activates repeatedly, not just once.

    To prevent a titanium film forming on electrical insulators or other sensitive surfaces, the filament is often mounted in a shroud. A large conductance between shroud and chamber does not limit the inherent pumping speed of the Ti film. Frequently, the shroud surface is cooled with LN2 (presumably because the gas molecule's longer residence time increases reaction probability while the lower temperature decreases the reaction rate).

    The titanium sublimation pump rarely works as the only high vacuum pump in a system; rather it works as a supplementary pump in a number of very specific applications. For example, where a vacuum system must be rapidly cycled from atmosphere to pressures approaching UHV, a correctly operated Ti sub pump removes active gases in the pressure range from 10^-5 to 10^-8 torr. If a process in a vacuum chamber requires a continuous, or intermittent loading of an active gas, but must be periodically pumped to low pressure, we recommend a Ti sub pump because of its high pumping speed and low cost. The Ti sub pump most often finds application, however, as an adjunct to an ion pump in UHV systems.

    In all applications, the Ti sub pump removes the active gases (any gas that chemically reacts with titanium, such as: nitrogen, oxygen and hydrogen). In fact, combining a Ti sub pump and turbo pump in one chamber gives excellent pumping speed and low ultimate pressures for all gases except helium.