Performance of new crystal cathode pressure gauges for long-pulse operation in the Wendelstein 7-X stellarator.

To improve the reliability of the ASDEX pressure gauges in the plasma vessel of the Wendelstein 7-X stellarator, nine of them were equipped with a LaB6 crystal electron emitter for the first time. These crystal cathode pressure gauges were operated during the last campaign in 2018 (operation phase 1.2b) with only 2 A heating current for over 40 h in a magnetic field of about 2.1 T without failure. Owing to this excellent performance, we have decided to equip all pressure gauges with crystal cathodes for the next campaign of Wendelstein 7-X (operation phase 2). We report on a pretest in a superconducting magnet, show a measurement of the neutral pressure in Wendelstein 7-X, and demonstrate the long-term stability of the crystal cathode pressure gauges.