TUBO effusion sources

Imagine a source that offers operating temperatures well above 2000 °C. Imagine a source that is ultrapure because it consists entirely of refractory metals in the hot region.

Impossible? Here it is.

The TUBO source uses a tubular filament that encloses the entire crucible. The electrons flow along the source axis, up through the heat insulation shields and down through the filament. Like this, the electrical insulators can be placed well below the hot zone of the source, thus allowing extremely high temperatures. The antiparallel direction of the heater current suppresses the generation of magnetic fields. The crucible temperature is controlled via a thermocouple at the bottom of the crucible, providing the highly precise temperature control, stability and reproducibility of a standard effusion source.

The filament can be made conical to achieve hot lip or cold lip operation of the source, depending on the specific requirements of the source material/crucible combination.

For still higher temperatures, the TUBO e version of the source features an electron emission booster heater. In this configuration, the crucible is held at a positive high voltage so that electrons leave the filament and provide electron beam heating of the crucible. The source geometry and electrical design are chosen in such a way that the electron emission heater passively follows the filament heater, providing additional power at high temperatures without having to implement a separate control loop.