Speaker
Description
The diagnostic residual gas analyzer (DRGA) at Wendelstein 7-X (W7-X) provides remote measurements of the exhaust gas composition sampled from the sub-divertor region. A new compact time-of-flight mass spectrometer has been installed and operated routinely during the latest operation campaign OP2.3. It records full mass spectra, enabling comprehensive monitoring of exhaust-gas dynamics. The system achieves a temporal resolution of 0.1 s and a mass resolution of approximately m/Δm = 500 at mass 4. Both raw spectral data and directly processed data for a predefined set of masses are available, facilitating rapid trend analysis as well as detailed post-processing.
The measurement fidelity allows for the analysis of trace gases. Two applications are presented.
First, an enrichment study of Neon between the core plasma, divertor, and exhaust was carried out during experiments with auxiliary Neon seeding for edge-radiation control. No significant impurity enrichment was observed.
Second, helium transport in the sub-divertor region is examined by comparing measured signal ratios. The measured concentrations match well with the model results.
At present, these analyses are limited to relative signal intensities, as no absolute calibration has yet been performed. Calibration of the instrument response and determination of the transfer function between the sub-divertor and the analysis chamber are planned.
Initial measurements using a He–D₂ gas mixture have been successfully performed. The resulting spectra show a clear separation of the expected mass peaks, confirming the system’s capability to distinguish species of similar mass. This represents an important preparatory step for the W7-X deuterium campaign currently in preparation.
These results demonstrate the utility and versatility of the instrument.