THE REVERSED FIELD PINCH L Marrelli, P. Martin, M Puiatti, J Sarff, B. Chapman, J Drake, Dominique Escande, S Masamune To cite this version: L Marrelli, P. Martin, M Puiatti, J Sarff, B. Chapman, et al.. THE REVERSED FIELD PINCH. 2020. hal-02505414 HAL Id: hal-02505414 https://hal.archives-ouvertes.fr/hal-02505414 Preprint submitted on 11 Mar 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THE REVERSED FIELD PINCH L. Marrelli1,2, P. Martin1,3, M.E. Puiatti1,2, J. S. Sarff4, B. E. Chapman4, J. R. Drake5, D. F. Escande6, S. Masamune7,8 1Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy 2 CNR-ISTP, Corso Stati Uniti 4, 35127 Padova, Italy 3 Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Padova, Italy 4 Department of Physics, University of Wisconsin, Madison, WI, United States of America 5 Royal Institute of Technology KTH, SE-10044 Stockholm, Sweden 6 Aix-Marseille Universitè, CNRS, PIIM, UMR 7345, Marseille, France 7 Kyoto Institute of Technology, Kyoto 606-8585, Japan 8 Chubu University,1200, Matsumoto-cho, Kasugai-shi, Aichi 487-8501, Japan Abstract. This paper reviews the research on the Reversed Field Pinch in the last three decades. Substantial experimental and theoretical progress and transformational changes have been achieved since the last review (Bodin, 1990). The experiments have been performed in devices with different sizes and capabilities. The largest one are RFX-mod in Padova (Italy) and MST in Madison (US). The experimental community includes also EXTRAP -T2R in Sweden, RELAX in Japan and KTX in China. Impressive improvements in the performance are the result of exploration of two lines: the high current operation with the spontaneous occurrence of helical equilibria with good magnetic flux surfaces and the active control of the current profile. A crucial ingredient for the advancements obtained in the experiments has been the development of state-of-art active feedback control systems allowing the control of MHD instabilities in presence of a thin shell. Contributions of the RFP line to the fusion grand challenge will be reported. The balance between achievements and still open issues leads us to the conclusion the RFP can be a valuable and diverse contributor in the quest for fusion electricity. Contents Abstract. ............................................................................................................................................... 1 Introduction .......................................................................................................................................... 3 1 Narrative summary ....................................................................................................................... 5 2 RFP basics .................................................................................................................................. 11 2.1 Cylindrical equilibrium and basic linear stability .............................................................. 11 2.2 The RFP devices ................................................................................................................ 13 3 Magnetic self-organization in the RFP ...................................................................................... 15 3.1 The RFP turbulent dynamo in single fluid approximation ................................................ 16 3.2 The Hall dynamo in two-fluid MHD ................................................................................. 19 3.3 Measurements of the RFP dynamo and momentum transport ........................................... 20 3.4 Emergence of a new interpretation of viscoresistive simulations: the helical ohmic state 21 3.5 Electrostatic nature of the RFP dynamo ............................................................................ 23 3.6 Emergence of helical states in experiments ....................................................................... 24 3.7 Experimental reconstruction of helical equilibria .............................................................. 25 3.8 Driven helical states. .......................................................................................................... 26 3.9 Further theoretical results................................................................................................... 28 4 Transport and confinement in the Multiple Helicity and Quasi Single Helicity RFP ............... 30 4.1 Core heat transport and confinement ................................................................................. 31 Multiple Helicity states .................................................................................................. 31 Quasi Single Helicity states ........................................................................................... 33 4.2 Particle transport and confinement .................................................................................... 35 4.3 Effect of microinstabilities ................................................................................................. 37 4.4 Effect of reconnection events ............................................................................................. 37 4.5 Edge transport and turbulence ............................................................................................ 39 4.6 Isotopic effect ..................................................................................................................... 41 4.7 Fast ion confinement .......................................................................................................... 41 5 Current profile control ............................................................................................................... 43 5.1 Foundations for current profile control .............................................................................. 43 5.2 Inductive techniques .......................................................................................................... 44 5.3 Current profile modification and fluctuation reduction ..................................................... 45 5.4 Improved fusion performance ............................................................................................ 47 5.5 Confinement scaling .......................................................................................................... 51 5.6 Emergence of microinstability in PPCD plasmas .............................................................. 52 5.7 Toward non-inductive (dc) current profile control ............................................................ 52 5.8 Other routes to improved confinement .............................................................................. 53 5.9 Open questions and future directions ................................................................................. 55 6 and density limit ...................................................................................................................... 57 6.1 High plasmas ................................................................................................................... 57 6.2 Density limits ..................................................................................................................... 59 6.3 Neoclassical bootstrap current at high ............................................................................ 62 7 Active control of MHD stability ................................................................................................ 63 7.1 Resistive Wall Modes ........................................................................................................ 63 Theoretical studies on RWM stabilisation ..................................................................... 64 The Intelligent Shell geometry ....................................................................................... 65 The Mode Control algorithms ........................................................................................ 67 Influence of control coils field sidebands and their aliasing on MHD control .............. 67 Experimental demonstrations of RWM stabilization ..................................................... 68 Advanced topics in RWM control ................................................................................. 69 7.2 Tearing Modes in the RFP ................................................................................................. 72 Wall and phase locking of Tearing Modes .................................................................... 73 Mitigation techniques of TM wall locking .................................................................... 75 Modeling of TM phase dynamics under feedback control: limits of CMC control ....... 76 8 Plasma-wall interactions ............................................................................................................ 78 8.1 Effect of magnetic topology on plasma-wall interaction ................................................... 78 8.2 Recycling control ..............................................................................................................