Bartholomäus Jagielski

• This work describes advanced neutral gas pressure gauges for the use in strong mag-netic fields during plasma operation of fusion devices, such as inside large stellarators and the International Thermonuclear Experimental Reactor (ITER; latin: way, path). In these environments, different factors compromise the performance of commercially available pressure gauges. Based on an existing design of the Axialsymmetrical Divertor-Experiment (ASDEX) pressure gauge, a manometer head with a novel cathode was developed. Differ-ent cathode geometries and materials, consisting of lanthanum hexaboride (LaB6), zirconi-um carbide (ZrC), hafnium carbide (HfC) and thoriated tungsten, were systematically in-vestigated to reveal their sensitivity in different gas atmospheres, magnetic field strengths and pressure ranges. In addition, thermo-mechanical loads and temperature limits were analyzed, as well as electrical stability as a function of the magnetic field and the condi-tioning properties. The focus lies in the development and characterization of novel elec-tron emitters and the understanding and optimization of their performance under typical operating conditions expected in large fusion devices. The results presented here suggest that neutral gas manometers equipped with LaB6 emitters are best suited for use in W7-X and have already been selected to replace ma-nometers with tungsten cathodes. An evaluation of the use of LaB6 cathodes in ITER and future fusion facilities with planned deuterium-tritium (DT) operation requires a detailed study of the performance of the emitters under neutron bombardment, since LaB6 is known to have a large neutron cross section. The use of pure Boron-11 is proposed to avoid this.