Dynamics of ultralow-q plasmas in the RFX-mod device. (1st June 2022)

• Record Type: Journal Article
• Authors: Zuin, M.; Agostini, M.; Auriemma, F.; Bonfiglio, D.; Cappello, S.; Carraro, L.; Cavazzana, R.; Cordaro, L.; Franz, P.; Marrelli, L.; Martines, E.; Puiatti, M.E.; Piovan, R.; Spizzo, G.; Terranova, D.; Vianello, N.; Zanca, P.; Zaniol, B.; Zanotto, L.
• Is Part Of: Nuclear fusion. Volume 62:Number 6(2022)
• Publication Date: 2022-06-01
• Subjects: ultra low q -- RFP -- MHD -- magnetic confinement -- reconnection -- mode control; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/ac58a7
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: The results are presented of an experimental activity performed in the RFX-mod device aimed at characterizing plasma dynamics in the so-called Ultralow-q (ULq) magnetic configuration, which corresponds to edge safety factor values below 1. The role of the edge safety factor in determining plasma dynamics is studied. In particular, a characterization of MHD activity is performed. The results of dedicated non-linear 3D visco-resistive MHD simulations are in good quantitative agreement with the experimental observations. In particular, the predicted tendency for ULq plasmas to be characterized by magnetic spectra dominated by a single mode (either a kink or a double resonant internal mode) is confirmed by experiment. Magnetic reconnection plays a relevant role in determining the dynamics of the magnetic topology. Both almost quiescent and largely fluctuating plasmas are observed with a strong sensitivity on the edge safety factor. The main MHD properties of the ULq are compared to those of RFP and tokamak discharges, also produced in the RFX-mod device. MHD modes exhibit toroidal rotation at a frequency depending on mode amplitude. Differently from what encountered in RFP plasmas at comparable current levels, no wall locking is detected.