Motivations and perspectives of RFX-mod2, the challenge of the upgraded RFX-mod device

摘要

Introduction In recent years the RFX-mod [1] device has been operated as a Reversed Field Pinch (RFP) and as a low-q Tokamak, and recently the H-mode has been achieved by electrode biasing in circular and Single Null configuration [2]. In both configurations the capability and flexibility of its active control system of MHD instabilities have been exploited to control RWMs and tearing mode wall locking (RFP) and to stabilize the m/n=2/l mode to operate at q(a)<2 (Tokamak). The dynamics of the tearing modes has been fully characterized experimentally, and simulated by the RFXLocking code [3]. At high plasma current (Ip>lMA), RFP plasmas have been observed to self-organize into quasi single helicity (QSH) states, where a single m=l modes dominates the spectrum of all the other secondary modes and magnetic chaos is reduced. In particular, in QSH up to the SHAx states, where the main magnetic axis becomes the helical axis of the dominant mode [4], the best plasma performance is observed at the lowest amplitude of the secondary modes.