Abstract
The composition of exhausted gas is a key parameter in long-pulse plasma fusion experiments, and its evolution shall be monitored at timescales relevant to plasma dynamics and plasma-wall interactions. A diagnostic residual gas analyzer (DRGA) is a multisensor instrument particularly suited to these studies, and ITER will adopt DRGAs in the equatorial and in the divertor tokamak regions. In this work, we have revisited the design of the ITER divertor DRGA through simple vacuum analytical considerations supported by simulations conducted with Molflow+, a test particle Monte Carlo (TPMC) simulation code commonly used in the particle accelerator community. Starting with recommendations on the manufacturing of the vacuum piping of the DRGA, this work is followed by a complete vacuum characterization of the diagnostic vacuum setup (pressure profiles at base pressure and during sampling, orifice diameter, and length optimization), and finally, the in-vessel residence time of the most important gas species is simulated. These studies have allowed us to give insights into some experimental results recently found on the prototype DRGA installed in the Wendelstein W7-X stellarator.
| Original language | English |
|---|---|
| Pages (from-to) | 629-640 |
| Number of pages | 12 |
| Journal | Fusion Science and Technology |
| Volume | 77 |
| Issue number | 7-8 |
| DOIs | |
| State | Published - 2021 |
Funding
This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the peer-reviewed, accepted form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-publicaccess-plan ). The authors would like to thank M. Ady, CERN Geneva, for valuable discussions on Molfow+. Also, information exchanges with IPP-Greifswald?s G. Schlisio on the W7-X DRGA system configuration and early results are very much appreciated. Finally, the authors wish to thank D. E. Williamson, Oak Ridge National Laboratory US ITER Project Office, for his continuous support of the initiative to optimize the pumping aspects specific to ITER diagnostic systems with direct vacuum connection to the main torus, as in the case of the DRGA. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the peer-reviewed, accepted form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-publicaccess-plan).
Keywords
- Diagnostic residual gas analyzer
- ITER
- Molflow+
- Wendelstein W7-X