0617281 - ÚFP 2025 RIV CZ eng O - Others
Weinzettl, Vladimír - Vartanian, S. - Dejarnac, Renaud - Jeřáb, Martin - Havránek, Aleš - Jaulmes, Fabien - Dimitrova, Miglena - Naydenkova, Diana
First partial pressure measurements using Optical Penning Gauge in the COMPASS tokamak.
2024
Institutional support: RVO:61389021
Keywords : COMPASS * measurement * tokamak
OECD category: Fluids and plasma physics (including surface physics)
Result website:
https://soft2024.eu/wp-content/uploads/2024/09/SOFT-2024_Book-of-Abstracts_20-09-2024.pdf

The Optical Penning Gauge (OPG) for partial pressure measurements has been successfully implemented in the bottom high-field side diagnostic port in the COMPASS tokamak. The OPG diagnostic was based on an Alcatel CF2P type and two photomultipliers covered with interference filters as fast detectors. The procedure of its implementation on COMPASS is described in detail, mentioning technical improvements such as a new 3D printed light-proof shield and fine optics refocusing, leading to a doubling of the light collection efficiency, demonstrated on the measured calibration curves. Calibration data for deuterium (using 486 nm), helium (using 728 nm), nitrogen (around 820 nm) and argon (around 810 nm) are discussed, including the effect of deuterium pressure on the helium channel. Time-resolved measurements of the working gas (deuterium) and main gaseous impurity (helium) show, how helium, used for glow discharge cleaning, is subsequently released from the plasma-facing components during the following shot. Also, a typical behaviour of both the gasses in L-mode, ELM-free and ELMy H-mode regimes, and even just after the main (high-current high-temperature) discharge is exemplified. Surprisingly long, low-current post-discharges (2-3 kA, about 100 ms), predominantly in helium, were observed by the OPG but further also confirmed by an overview high-speed visible camera and by photomultipliers focused to the plasma edge. The OPG results were compared with a wide-range pressure gauge installed at the miplane on the low-field side, revealing similarities but also differences in both the time behaviour and magnitude. The values of the tokamak vacuum vessel pre-fill and the following gas puff, both extracted either from the calibrated gas puff piezo-valve or from the above-mentioned gauges, are compared to those required by the DYON code to achieve reasonable agreement with the measured plasma current, density and temperature for breakdown and burn-through discharge phases.
Permanent Link: https://hdl.handle.net/11104/0364229