Mitigation of plasma-wall interactions with low-Z powders in DIII-D high confinement plasmas

• Published in: arXiv.org
• Main Authors: Effenberg, Florian, Bortolon, Alessandro, Casali, Livia, Nazikian, Raffi, Bykov, Igor, Scotti, Filippo, Wang, Huiqian Q, Fenstermacher, Max E, Lunsford, Robert, Nagy, Alexander, Grierson, Brian A, Laggner, Florian M, Maingi, Rajesh, the DIII-D Team
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 16.08.2022
• Subjects: Boron; Boron nitride; Confinement; Lithium; Oxygen content; Physics - Applied Physics; Physics - Plasma Physics; Plasmas (physics)
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2203.15204

Experiments with low-Z powder injection in DIII-D high confinement discharges demonstrated increased divertor dissipation and detachment while maintaining good core energy confinement. Lithium (Li), boron (B), and boron nitride (BN) powders were injected in high-confinement mode plasmas (\(I_p=\)1 MA, \(B_t=\)2 T, \(P_{NB}=\)6 MW, \(\langle n_e\rangle=3.6-5.0\cdot10^{19}\) m\(^{-3}\)) into the upper small-angle slot (SAS) divertor for 2-s intervals at constant rates of 3-204 mg/s. The multi-species BN powders at a rate of 54 mg/s showed the most substantial increase in divertor neutral compression by more than an order of magnitude and lasting detachment with minor degradation of the stored magnetic energy \(W_{mhd}\) by 5%. Rates of 204 mg/s of boron nitride powder further reduce ELM-fluxes on the divertor but also cause a drop in confinement performance by 24% due to the onset of an \(n=2\) tearing mode. The application of powders also showed a substantial improvement of wall conditions manifesting in reduced wall fueling source and intrinsic carbon and oxygen content in response to the cumulative injection of non-recycling materials. The results suggest that low-Z powder injection, including mixed element compounds, is a promising new core-edge compatible technique that simultaneously enables divertor detachment and improves wall conditions during high confinement operation.