Catalytic probes for measuring H distribution in remote parts of hydrogen plasma reactors

Catalytic probes for measuring the H density in remote parts of hydrogen plasma reactors are presented. The probe allows for determination of the H density in its vicinity by measuring the heat dissipated on its tip due to catalytic heterogeneous surface recombination of H atoms. Since the probe is made small, it does not disturb the original concentration of the atoms much. By moving the probe through the vessel it is possible to measure the distribution of H density in the entire vessel. The probe was successfully applied for measuring the H density in remote parts of different hydrogen plasma reactors. Depending on discharge parameters, different values were obtained ranging from 1 × 1020 to 6 × 1021 m−3. The H density depends on the recombination coefficient of the discharge vessel. In the case of borosilicate glass, the recombination coefficient is stable and low enough to enable a high H density. In the case of Pyrex, the recombination coefficient increases with the chamber temperature leading to a huge decrease of H density as the wall is heated.