Titanium sublimation pump
The titanium sublimation (TSP) is a special ultra-high vacuum - pump based on the high gettering capability of freshly vapor deposited titanium based: The titanium is a highly pure chilled Adsorberfläche evaporated intercepts there who happen impinging gas atoms by pure chemisorption . Gases such as oxygen , nitrogen or carbon dioxide can be chemically bonded to the titanium. This distinguishes it from the ion getter pump , in which the gas to be pumped has to be ionized beforehand in order to then direct it to the adsorber surface in a targeted manner in a static electric field.
In simple terms, the titanium surface - ie the condensed titanium - “catches” (en .: “to get”, hence “getter”) the last gas molecules that are still in the vacuum. After a while the titanium surface is dirty again; a new evaporation cycle regenerates them.
The effectiveness of a TSP depends heavily on the pressure and v. a. the elements contained in the residual gas . If the pressure is too high, the fresh titanium surface quickly becomes dirty again, so that the time between the vapor deposition phases must be very short. However, if this time is too short, the pump will heat up considerably. Atoms can then detach themselves from the wall again through thermal effects. One possibility to prevent this is by cooling the wall with water or liquid nitrogen (see below). The pump is mainly used to evacuate particle accelerators .
LN 2 for cooling the TSP
Often, liquid nitrogen is used to cool the walls of a TSP . There are several reasons for this:
- The walls do not get warm, which prevents the thermal desorption of the already bound residual gas atoms.
- The cold walls act as a cryopump .
- At the temperature of liquid nitrogen, the titanium does not condense as a thin layer, but rather tends to clump. This increases the surface area, which effectively increases the pumping capacity.