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P: Fachverband Plasmaphysik

P 9: Poster I

P 9.5: Poster

Dienstag, 29. März 2022, 16:00–17:30, P

Study of LaB6-Cathodes in Neutral Pressure Gauges for Strong Magnetic Fields — •Bartholomäus Jagielski^1,2, Uwe Wenzel¹, Mirko Marquardt¹, Jiawu Zhu¹, and Thomas Sunn Pedersen¹ — ¹Max Planck Institute for Plasma Physics, Greifswald, Germany — ²Physical Institute of the University Greifswald, Greifswald, Germany

The neutral gas pressure measurement is a key diagnostic for scrape-off-layer physics, that gives a direct indication of the exhaust rate. However, strong magnetic fields and the requirement for the longevity of diagnostics in increasingly longer lasting plasma pulses, is a major challenge. For this reason, we developed and tested new crystal-cathode pressure gauges with different cathode geometries made of lanthanum hexaboride (LaB6), which can permanently withstand the Lorentz-Forces. For the next campaign of Wendelstein7-X, mono- and polycrystalline LaB6-cathodes have been operated in a specially prepared laboratory, equipped with a superconducting magnet, which provides magnetic field strengths of up to 5.9 T, in a wide range of neutral pressure values, as well as several different working gases. NIR-thermionic investigations have been conducted, cross-checked with ANSYS simulations. The Anode potential has been optimized and we compared several different cathode lengths, ranging from 5mm to 8mm, for different electron emittances. A significant decrease of the required heating current of the shorter variants has been observed. Furthermore, we tested a new two-rod-cathode design, heated by three pyrolytic graphite blocks, showing noticeably improved performance.