Characterization of wall conditions in Uragan-2M stellarator using stainless steel thermal desorption probe

Abstract

The method and device have been developed and used for operative estimation of impurity level, outgassing rate and molecular layers number on high vacuum chamber surfaces of magnetic confinement fusion devices in situ. The method is based on the thermal desorption of gases into a vacuum vessel from the surface of a special metal probe during its heating up to temperature of 300 °C. To investigate and use this method, the probe was designed, manufactured and installed into the vacuum vessel of the Uragan-2 M stellarator. The technique was tested after applying VHF/RF cleaning discharges in different scenarios. A decrease of the released gas amount from the surface by more than one order of magnitude was recorded. The mass-spectrometer registered the atomic masses 18 u (H2O), 28 u (CO + N2) and 44 u (CO2), as the main gases desorbed from the probe surface during its heating. Heavy hydrocarbon masses (mainly 58 u) were also registered. The method had also been tested in the regime of hydrogen gas retained in the wall.