The RFX-mod2 device [0] will follow the path of the RFX-mod experiment as a multi-configuration machine. Different configurations and scenarios will be studied given the high flexibility of its power supplies and control system going from the Reversed Filed Pinch to the tokamak and ultra-low q configurations. The changes to the machine are expected to improve plasma performances, allow better measurements and explore regimes (such as shaped tokamak equilibria also with negative triangularity) that were only tested in RFX-mod. In view of the restart of operations (in late 2024) predictive studies are being carried out on the expected plasma state in terms of magnetic field fluctuations amplitude, equilibrium configuration, particle and energy confinement time as well as the evaluation of plasma control issues and performances given the new system of magnetic sensors in the different plasma configurations (i.e. RFP and tokamak). In addition to consolidating the understanding and potentiality of spontaneous RFP helical regimes (QSH), the renewed facility RFX-mod2 is expected to facilitate the exploration of the stimulated helical regimes, based on the application of Magnetic Perturbations (MP) to select the helical pitch of the resulting QSH states. Indeed, a favorable action of MP is expected on the basis of preliminary 3D nonlinear MHD simulations, indicating a reduction of secondary modes amplitudes, and an increase of the ratio dominant/secondary modes amplitude, consistently with a favorable plasma-wall proximity of b/a=1.04 (instead of b/a=1.1 of RX-mod) [1]. In particular, a more efficient magnetic chaos healing effect has been envisaged to occur in QSH regimes based on non-resonant MPs, by means of 3D nonlinear MHD simulations. Such regimes have been preliminarily tested in RFX-mod [2]. Different helical pitches of QSH regimes are shown to involve different magnetic shear profiles (from monotonic to shear reversed safety factor profiles) whose impact on transport properties could provide insight on underlying transport mechanism. In this respect it is expected that also RFX-mod 2 will show helical equilibria and the associated internal transport barrier experimentally observed in RFX-mod. MHD analyses suggest that a lower level of magnetic perturbation is to be expected (around 25% reduction) with possibly an increase in the ratio between dominant and secondary modes (a favourable trend as shown in [3]). This is quite a promising result given the fact that residual stochasticity in SHAx states seems still to play a role in the barrier formation. In RFX- mod two candidates were considered as responsible for the energy transport at the internal barrier: secondary tearing modes and micro-tearing modes [4,5]. We aim at providing an estimate of particle and energy confinement in RFX-mod2 within a predictive scheme as performed in [3]. The ASTRA [6] and orbit [7] codes will be used to provide information on the expected particle diffusion in a self-consistent way and this will allow an indirect estimate of the energy transport (?eff) again in the assumption of a dominant chaotic mechanism. In this respect, the new diagnostics system to measure internal kinetic profiles expected for RFX- mod2 will allow a better experimental characterization and provide additional input to the codes in terms of time evolution of temperature profiles, particle sources (both main gas and impurities) and neutrons production.
RFX-mod2 As Flexible Device For Reversed-Field-Pinch And Low-Field Tokamak Research
Terranova D
2023
Abstract
The RFX-mod2 device [0] will follow the path of the RFX-mod experiment as a multi-configuration machine. Different configurations and scenarios will be studied given the high flexibility of its power supplies and control system going from the Reversed Filed Pinch to the tokamak and ultra-low q configurations. The changes to the machine are expected to improve plasma performances, allow better measurements and explore regimes (such as shaped tokamak equilibria also with negative triangularity) that were only tested in RFX-mod. In view of the restart of operations (in late 2024) predictive studies are being carried out on the expected plasma state in terms of magnetic field fluctuations amplitude, equilibrium configuration, particle and energy confinement time as well as the evaluation of plasma control issues and performances given the new system of magnetic sensors in the different plasma configurations (i.e. RFP and tokamak). In addition to consolidating the understanding and potentiality of spontaneous RFP helical regimes (QSH), the renewed facility RFX-mod2 is expected to facilitate the exploration of the stimulated helical regimes, based on the application of Magnetic Perturbations (MP) to select the helical pitch of the resulting QSH states. Indeed, a favorable action of MP is expected on the basis of preliminary 3D nonlinear MHD simulations, indicating a reduction of secondary modes amplitudes, and an increase of the ratio dominant/secondary modes amplitude, consistently with a favorable plasma-wall proximity of b/a=1.04 (instead of b/a=1.1 of RX-mod) [1]. In particular, a more efficient magnetic chaos healing effect has been envisaged to occur in QSH regimes based on non-resonant MPs, by means of 3D nonlinear MHD simulations. Such regimes have been preliminarily tested in RFX-mod [2]. Different helical pitches of QSH regimes are shown to involve different magnetic shear profiles (from monotonic to shear reversed safety factor profiles) whose impact on transport properties could provide insight on underlying transport mechanism. In this respect it is expected that also RFX-mod 2 will show helical equilibria and the associated internal transport barrier experimentally observed in RFX-mod. MHD analyses suggest that a lower level of magnetic perturbation is to be expected (around 25% reduction) with possibly an increase in the ratio between dominant and secondary modes (a favourable trend as shown in [3]). This is quite a promising result given the fact that residual stochasticity in SHAx states seems still to play a role in the barrier formation. In RFX- mod two candidates were considered as responsible for the energy transport at the internal barrier: secondary tearing modes and micro-tearing modes [4,5]. We aim at providing an estimate of particle and energy confinement in RFX-mod2 within a predictive scheme as performed in [3]. The ASTRA [6] and orbit [7] codes will be used to provide information on the expected particle diffusion in a self-consistent way and this will allow an indirect estimate of the energy transport (?eff) again in the assumption of a dominant chaotic mechanism. In this respect, the new diagnostics system to measure internal kinetic profiles expected for RFX- mod2 will allow a better experimental characterization and provide additional input to the codes in terms of time evolution of temperature profiles, particle sources (both main gas and impurities) and neutrons production.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
