L. Piron

L. Piron
Italian National Research Council | CNR

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57
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1,303
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Publications

Publications (57)
Article
Full-text available
The JET hybrid scenario has been developed from low plasma current carbon wall discharges to the record-breaking Deuterium-Tritium plasmas obtained in 2021 with the ITER-like Be/W wall. The development started in pure Deuterium with refinement of the plasma current, and toroidal magnetic field choices and succeeded in solving the heat load challeng...
Article
The RAPTOR suite of codes combines real-time model-based predictions of the plasma state with the available diagnostic measurements. Following the work on TCV and ASDEX-Upgrade, this paper presents the implementation of the RAPTOR suite for JET. This suite embeds: the upgraded equilibrium reconstruction EQUINOX code, the new FLUXMAP algorithm, whic...
Article
Operation of a magnetic fusion experiment, such as JET, relies on the availability of real-time (RT) control schemes, which supervise the plasma as it approaches the expected target performance while maintaining the integrity of the machine and its subsystems. At JET, there have been a series of recent efforts since (Lennholm M. et al 2017 Fusion E...
Article
In magnetic fusion devices, unwanted non-axisymmetric magnetic field perturbations, known as error fields (EF), can have detrimental effects on plasma stability and confinement. Such EFs may originate from several sources, such as axi-symmetric coil misalignments, coil feeds, 3D structures in the wall surrounding the plasma, presence of ferromagnet...
Article
The mega amp spherical tokamak (MAST) was a low aspect ratio device (R/a = 0.85/0.65 ∼ 1.3) with similar poloidal cross-section to other medium-size tokamaks. The physics programme concentrates on addressing key physics issues for the operation of ITER, design of DEMO and future spherical tokamaks by utilising high resolution diagnostic measurement...
Article
Operations using deuterium-tritium (DT) mixtures are envisaged in JET device in the forthcoming 2020 experimental campaign. These experiments will offer a unique possibility to study several open issues in support to ITER and DEMO, such as alpha particle heating, and to improve the high plasma performance obtained in the previous DT campaign Keilha...
Article
This paper reports the main recent results of the RFX-mod fusion science activity. The RFX-mod device is characterized by a unique flexibility in terms of accessible magnetic configurations. Axisymmetric and helically shaped reversed-field pinch equilibria have been studied, along with tokamak plasmas in a wide range of q(a) regimes (spanning from...
Article
This work presents the first evidence of helical flow in RFX-mod q(a) < 2 tokamak plasmas. The flow pattern is characterized by the presence of convective cells with m = 1 and n = 1 periodicity in the poloidal and toroidal directions, respectively. A similar helical flow deformation has been observed in the same device when operated as a reversed f...
Article
Disruptions caused by tearing modes (TMs) are considered to be one of the most critical roadblocks to achieving reliable, steady-state operation of tokamak fusion reactors. Here we have demonstrated a promising scheme to avoid mode locking by utilizing the electro-magnetic (EM) torque produced with 3D coils that are available in many tokamaks. In t...
Article
The RFX-mod device is operated both as a reversed field pinch (RFP), where advanced regimes featuring helical shape develop, and as a tokamak. Due to its flexibility, RFX-mod is contributing to the solution of key issues in the roadmap to ITER and DEMO, including MHD instability control, internal transport barriers, edge transport and turbulence, i...
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We present experimental results of magnetic feedback control on the m=2, n=1 tearing mode in RFX-mod operated as a circular ohmically heated tokamak. The feedback suppression of the non-resonant m=2, n=1 Resistive Wall Mode (RWM) in q(a)<2 plasmas is a well-established result of RFX-mod. The control of the tearing counterpart, which develops in q(a...
Article
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Magnetic feedback control of the resistive-wall mode has enabled the DIII-D tokamak to access stable operation at safety factor q_{95}=1.9 in divertor plasmas for 150 instability growth times. Magnetohydrodynamic stability sets a hard, disruptive limit on the minimum edge safety factor achievable in a tokamak, or on the maximum plasma current at a...
Article
Recent DIII-D and RFX-mod experiments have demonstrated stable tokamak operation at very low values of the edge safety factor q(a) near and below 2. The onset of n = 1 resistive wall mode (RWM) kink instabilities leads to a disruptive stability limit, encountered at q(a) = 2 (limiter plasmas) and q 95 = 2 (divertor plasmas). However, passively stab...
Article
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The plasma–wall interaction (PWI) in the reversed field pinch is strongly influenced by three-dimensional edge magnetic topology. This is true both in the chaotic regime, where several modes interact producing a toroidally localized bulge, and in the helical state, which helically modulates the edge profiles. In both regimes an external region with...
Article
Plasma rotation has been one of the topics of major interest in the fusion community over the last few years, given in particular its role on magnetohydrodynamic stability and turbulence suppression. Rotation can be affected by three-dimensional (3D) magnetic fields, e.g. due to intrinsic magnetic field errors or active coils. The reversed field pi...
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Recent evidence has demonstrated the efficacy of Virtual Reality (VR) for stroke rehabilitation nonetheless its benefits and limitations in large population of patients have not yet been studied. To evaluate the effectiveness of non-immersive VR treatment for the restoration of the upper limb motor function and its impact on the activities of daily...
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RFX-mod [Sonato et al., Fusion Eng. Des. 66, 161 (2003)] exploits its 192 active coils in both reversed-field pinch (RFP) and tokamak configurations with varying degrees of 3D shaping, providing also a test bed for validating stellarator codes and 3D nonlinear magnetohydrodynamic codes. This makes RFX-mod a unique and flexible facility for comparat...
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Background. Haptic robots allow the exploitation of known motor learning mechanisms, representing a valuable option for motor treatment after stroke. The aim of this feasibility multicentre study was to test the clinical efficacy of a haptic prototype, for the recovery of hand function after stroke. Methods. A prospective pilot clinical trial was p...
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A survey of the feedback algorithms exploiting radial sensors applied in RFX-mod is presented. A Fourier variant of the ‘intelligent shell’, whose efficiency is limited by the aliasing coming from the active coils' sideband harmonics, and ‘clean mode control’, a method to single out and cancel this pollution, are compared for both tearing mode and...
Article
In the reversed field pinch experiment RFX-mod, plasma currents larger than 1 MA show a spontaneous transition from an axisymmetric to a helical configuration, where electron internal transport barriers (eITB) are observed in the proximity of the maximum of the q safety factor. 3D MHD simulations predict a helical flow pattern associated with the h...
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This paper reports the highlights of the RFX-mod fusion science programme since the last 2010 IAEA Fusion Energy Conference. The RFX-mod fusion science programme focused on two main goals: exploring the fusion potential of the reversed field pinch (RFP) magnetic configuration and contributing to the solution of key science and technology problems i...
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An interesting result of magnetic chaos reduction in RFX-mod high current discharges is the development of strong electron transport barriers. An internal heat and particle transport barrier is formed when a bifurcation process changes the magnetic configuration into a helical equilibrium and chaos reduction follows, together with the formation of...
Article
A spontaneous transition to a helical equilibrium with an electron internal transport barrier is observed in RFX-mod as the plasma current is raised above 1 MA (Lorenzini R et al 2009 Nature Phys. 5 570). The helical magnetic equilibrium can be controlled with external three-dimensional (3D) magnetic fields applied by 192 active coils, providing pr...
Article
The wall of any magnetic fusion device is characterized by the presence of several 3D structures, such as portholes for diagnostics and for heating and current drive systems, coil feeds and other features. Time-varying magnetic fields induce eddy currents in the wall, whose pattern is modified by these structures, giving rise to magnetic field erro...
Article
Magnetic field errors can have a significant impact on the confinement properties of magnetized fusion plasmas. In the RFX-mod reversed-field pinch (Sonato et al 2003 Fusion Eng. Des. 33 161) a significant error field is produced during the current ramp by the eddy currents induced in the 3D wall structures, such as the gaps and some large porthole...
Article
This paper summarizes the main achievements of the RFX fusion science program in the period between the 2008 and 2010 IAEA Fusion Energy Conferences. RFX-mod is the largest reversed field pinch in the world, equipped with a system of 192 coils for active control of MHD stability. The discovery and understanding of helical states with electron inter...
Article
Full-text available
The wall of any magnetic fusion device is composed of various 3D structures, such as large portholes, gaps, coil feeds, and other features. These can affect plasma stability, inducing magnetic field errors, coupling different modes, or increasing their growth rate. These effects should thus be considered in any MHD feedback control approach. Exampl...
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The full three-dimensional (3D) approach is now becoming an important issue for all magnetic confinement configurations. It is a necessary condition for the stellarator but also the tokamak and the reversed field pinch (RFP) now cannot be completely described in an axisymmetric framework. For the RFP the observation of self-sustained helical config...
Article
The achievement of plasmas with current values close to the maximum design point of 2 MA for the operation of RFX-mod Reversed Field Pinch (RFP) involved acting on three key issues: the RFP start-up method, the MHD equilibrium control and the plasma-wall interaction mitigation. The most effective start-up scheme for high current operation consisted...
Article
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In all major confinement devices (tokamaks, stellarators, spheromaks and reversed-field pinches—RFPs), a density limit has been found. Results summarized in a recent work by Puiatti et al (2009 Nucl. Fusion 49 045012) show that in the RFP high density does not cause a disruption, but a sequence of increasingly critical phenomena. First, at intermed...
Article
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The reversed field pinch configuration is characterized by the presence of magnetic structures both in the core and at the edge: in the core, at high plasma current the spontaneous development of a helical structure is accompanied by the appearance of internal electron transport barriers; at the edge strong pressure gradients, identifying an edge t...
Article
Full-text available
The reversed field pinch configuration is characterized by the presence of magnetic structures both in the core and at the edge: in the core, at high plasma current the spontaneous development of a helical structure is accompanied by the appearance of internal electron transport barriers; at the edge strong pressure gradients, identifying an edge t...
Article
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With the exploration of the MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for the reversed field pinch (RFP) magnetic configuration, and has made significant progress in understanding and improving confinement and in controlling plasma stability. A big leap with respect to previous k...
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In the quest for new energy sources, the research on controlled thermonuclear fusion1 has been boosted by the start of the construction phase of the International Thermonuclear Experimental Reactor2 (ITER). ITER is based on the tokamak magnetic configuration3, which is the best performing one in terms of energy confinement. Alternative concepts are...
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The reversed field pinch (RFP) is a magnetic configuration alternative to the tokamak that can be considered for a second generation of reactors. In this paper new remarkable results obtained in the RFP experiment RFX-mod are presented, showing that an internal transport barrier delimitates a large fraction of the plasma volume in a RFP when the cu...
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Optimization of machine operation, including plasma position control, density control and especially feedback control on multiple magnetohydrodynamic modes, has led RFX-mod to operate reliably at 1.5 MA, the highest current ever achieved on a reversed field pinch (RFP). At high current and low density the magnetic topology spontaneously self-organi...
Article
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The simultaneous use of feedback control for error field correction (EFC) and stabilization of an unstable resistive wall mode (RWM) has been demonstrated in DIII-D. While the conventional EFC method addresses error fields in a pre-programmed manner, it is challenged when an unstable RWM becomes dominant, because a weakly stable or feedback-stabili...
Article
The RFX-mod machine is equipped with the most advanced magnetic feedback system realized in a fusion device. With its 192 active coils, independently driven and fully covering the torus surface, RFX-mod is ideally suited to investigate different schemes for multi-mode feedback control of MHD modes and error fields. A great advance in the RFX-mod pe...

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