Speaker
Paolo Piovesan
(Consorzio RFX)
Description
This work investigates the formation of helical core equilibria in toroidal fusion plasmas, focusing on the role of dynamo, or magnetic flux pumping mechanisms in determining the equilibrium current profile. Dynamo effects determine the safety factor profile of the final 3D equilibrium, with important consequences on MHD stability and transport. We compare experimental results from multiple machines (RFX-mod, MST, AUG, DIII-D) and nonlinear MHD modelling. Two paradigmatic cases of helical state formation are considered and common physics is identified, by direct measurements of dynamo effects and MHD simulations: spontaneous formation in high-current reversed-field pinch (RFP) plasmas [1] and the hybrid scenario in high-beta tokamak plasmas [2]. Helical cores form in both cases, either spontaneously via saturation of MHD modes, or due to the marginally-stable ideal MHD response to external 3D fields. Direct measurements of the dynamo emf associated to 3D plasma distortions will be presented for a database of helical RFP plasmas from RFX-mod and MST, covering a wide range of plasma parameters. Similar measurements were also done in helical states forming in response to external 3D fields in Ohmic RFX-mod tokamak plasmas and in DIII-D high-beta hybrid plasmas. Experimental results qualitatively agree with nonlinear MHD modelling performed with the codes SpeCyl [3], PIXIE3D [4], and NIMROD [5]. They indicate that central current is redistributed by a dominantly electrostatic MHD dynamo. The underlying physics common to RFP and tokamak is thus revealed: a helical core displacement modulates parallel current density along flux tubes, which requires a helical electrostatic potential to build up, giving rise to a helical dynamo flow. Similar results were also recently obtained with the M3D-C1 code [6].
[1] R. Lorenzini et al., Nature Phys. 5, 570 (2009); [2] T.C. Luce et al., Nucl. Fusion 54, 013015 (2014); [3] D. Bonfiglio et al., Phys. Rev. Lett. 94, 145001 (2005); [4] D. Bonfiglio et al., Plasma Phys. Control. Fusion 57, 044001 (2015); [5] J.R. King, C.R. Sovinec, V.V. Mirnov, Phys. Plasmas 19, 055905 (2012); [6] S.C. Jardin et al., Phys. Rev. Lett. 115, 215001 (2015).
| Country or International Organization | Italy |
|---|---|
| Paper Number | EX/1-1 |
Primary author
Paolo Piovesan
(Consorzio RFX)
Co-authors
Dr
Barbara Zaniol
(Consorzio RFX, Padova, Italy)
Dr
Carlos Paz-Soldan
(General Atomics, San Diego, CA, USA)
Dr
Christopher T. Holcomb
(Lawrence Livermore National Laboratory)
Dr
Colin Chrystal
(Oak Ridge Associated Universities, Oak Ridge, TN, USA)
Dr
Daniele Bonfiglio
(Consorzio RFX, Padova, Italy)
Dr
David Terranova
(Consorzio RFX, Padova, Italy)
Dr
Dominique Escande
(Laboratoire PIIM, UMR 7345 CNRS-Aix Marseille Université, France)
Dr
Francesca Turco
(Columbia University)
Prof.
John Sarff
(University of Wisconsin-Madison)
Dr
Lidia Piron
(CCFE, Abingdon, UK)
Dr
Lionello Marrelli
(Consorzio RFX)
Dr
Luis Chacón
(Los Alamos National Laboratory, Los Alamos, NM, USA)
Mark Nornberg
(University of Wisconsin-Madison)
Dr
N.Z. Taylor
(Oak Ridge Associated Universities, Oak Ridge, TN, USA)
Dr
Paolo Franz
(Consorzio RFX, Padova, Italy)
Dr
Paolo Zanca
(Consorzio RFX, Padova, Italy)
Dr
Susanna cappello
(Consorzio RFX)
Dr
Timothy C. Luce
(General Atomics)
Dr
Valentin Igochine
(MPI für Plasmaphysik, Garching, Germany)
