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P: Fachverband Plasmaphysik

P 5: Poster I

P 5.26: Poster

Dienstag, 31. August 2021, 14:00–16:00, P

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

In order to evaluate the particle exhaust rate 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) nine newly developed Crystal Cathode Pressure Gauges (CCPG) were tested during pressure recordings. While cathodes from thoriated tungsten regularly bent under the influence of the j x B forces (2,1T), the CCPGs, equipped with emitters made of lanthanum hexaboride, functioned satisfactorily[1]. The LaB₆ cathodes of the CCPGs have a simple geometry and due to the low work function of 2.5eV, the heating current was reduced to 2-3 A in W7-X in hydrogen atmosphere, whereby the stress under Lorentz forces was further reduced[2]. This makes the LaB₆-emitter a promising candidate for precise manometers in a range between 10⁻⁶ and 1mbar and an application in future fusion plants (ITER, DEMO).

Recently three different cathode designs have been tested in different environmental conditions and compared: a 8mm and a 6mm long cathode, and a new 2-emitter design. Results of the investigations within an external magnetic field of 3T, latest optimization and future plans for the CCPGs are presented.

[1] U. Wenzel et al, J. Instrum.12(09), C09008 (2017).

[2] U. Wenzel et al, Rev. Sci. Instrum., 90, 123507 (2019).