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P: Fachverband Plasmaphysik

P 16: Poster Session 3

P 16.8: Poster

Mittwoch, 11. März 2020, 16:30–18:30, Empore Lichthof

Characterization of lanthanum-hexaboride electron emitters as cathodes in pressure gauges for strong magnetic fields — •Bartholomaeus Jagielski, Uwe Wenzel, Mirko Marquardt, Jiawu Zhu, Thomas Sunn Petersen, and the W7-X Team — Max Planck Institute for Plasma Physics, Greifswald, Germany

In order to evaluate the particle exhaust rate on the pumping ducts at the sub-divertor, the neutral gas pressure can be measured. In the last operation phase (OP 1.2) of the Wendelstein7-X (W7-X) pressure recordings took place with ASDEX Pressure Gauges (APG) and with newly developed Crystal Cathode Pressure Gauges (CCPG). While the cathodes from thoriated tungsten of the APGs regularly bent under the influence of the magnetic field (2,1T) and the resulting Lorentz forces, the CCPGs, equipped with an emitter made of lanthanum hexaboride, functioned largely without problems [1]. The simple cylindrical geometry, relatively high resilience to cathode poisoning, low workfunction (2.5eV) etc., makes the LaB6-emitter a promising candidate for future, precise manometers in a range between 1mbar to 10⁻⁶ mbar and for a successful application in future fusion plants (ITER, DEMO). For the next campaign of W7-X (OP 2.0) the LaB6-cathodes are being tested in different experimental environments and characterized with recent ANSYS simulations. The design, preliminary results of the investigations, with and without external magnetic field, and the latest optimization as well as future plans of/for the CCPGs are presented. [1] U. Wenzel et al, J. Instrum.12(09), C09008 (2017).