• Energy Research

Abstract Reconnection events in high current reversed field pinch plasmas are often associated to the partial or total loss of the helical magnetic topology. The electron temperature collapse during these phenomena is investigated in RFX-mod thanks to high time resolution soft-x-ray diagnostics; these data are used, together with magnetic energy reconstructions, for energy balance analysis. The paper shows that the energy released during reconnection events, similarly to astrophysical plasmas, might be involved in ion heating, the latter being estimated by the energy distribution function of neutral atoms, a rather interesting feature in a reactorial perspective. These issues will be further investigated in RFX-mod2 , an upgrade of the present device starting its operations from 2022, where the modified boundary conditions are expected to increase the helical states duration and reduce the frequency of reconnection events.

Abstract Reconnection events in high current reversed field pinch plasmas are often associated to the partial or total loss of the helical magnetic topology. The electron temperature collapse during these phenomena is investigated in RFX-mod thanks to high time resolution soft-x-ray diagnostics; these data are used, together with magnetic energy reconstructions, for energy balance analysis. The paper shows that the energy released during reconnection events, similarly to astrophysical plasmas, might be involved in ion heating, the latter being estimated by the energy distribution function of neutral atoms, a rather interesting feature in a reactorial perspective. These issues will be further investigated in RFX-mod2 , an upgrade of the present device starting its operations from 2022, where the modified boundary conditions are expected to increase the helical states duration and reduce the frequency of reconnection events.

Reconnection events in high current reversed field pinch plasmas are often associated to the partial or total transitions from a helical topology with conserved flux surfaces to a configuration characterized by a chaotic magnetic field. The electron temperature dynamic together with the magnetic energy reconstructions are used to evaluate the energy balance during these events and to quantify the associated dissipated power and released energy. A fraction of the energy released during reconnection events is involved in ion heating, as estimated by the energy distribution function of neutral atoms, a rather interesting feature in a reactorial perspective.

Reconnection events in high current reversed field pinch plasmas are often associated to the partial or total transitions from a helical topology with conserved flux surfaces to a configuration characterized by a chaotic magnetic field. The electron temperature dynamic together with the magnetic energy reconstructions are used to evaluate the energy balance during these events and to quantify the associated dissipated power and released energy. A fraction of the energy released during reconnection events is involved in ion heating, as estimated by the energy distribution function of neutral atoms, a rather interesting feature in a reactorial perspective.

In this paper we present our studies about the choices of anode design and operational regime in order to get high efficiency glow discharge cleaning of the first wall of a fusion device. We analyzed a database of toroidal and poloidal profiles of the ion current density at the wall, measured by electrostatic probes embedded in RFX-mod first wall tiles, taken in different configurations. The ion current at the wall, both global and local, is in fact strictly connected to the cleaning efficiency, since during glow discharge the wall is physically sputtered by the ions. We found that small size anodes and high in-vessel pressure lead to the peaking of the current profile around the anodes locations, and we experimentally characterized this effect. Instead, we found that anode radial position in the poloidal section has negligible effect on current density profile, even when the anodes are placed at the first wall. Finally, the most convenient operational regime, in terms of pressure and current, has been proposed.

In this paper we present our studies about the choices of anode design and operational regime in order to get high efficiency glow discharge cleaning of the first wall of a fusion device. We analyzed a database of toroidal and poloidal profiles of the ion current density at the wall, measured by electrostatic probes embedded in RFX-mod first wall tiles, taken in different configurations. The ion current at the wall, both global and local, is in fact strictly connected to the cleaning efficiency, since during glow discharge the wall is physically sputtered by the ions. We found that small size anodes and high in-vessel pressure lead to the peaking of the current profile around the anodes locations, and we experimentally characterized this effect. Instead, we found that anode radial position in the poloidal section has negligible effect on current density profile, even when the anodes are placed at the first wall. Finally, the most convenient operational regime, in terms of pressure and current, has been proposed.

Reconnection events in high current reversed field pinch plasmas are often associated to the partial or total transitions from a helical topology with conserved flux surfaces to a configuration characterized by a chaotic magnetic field. The electron temperature dynamic together with the magnetic energy reconstructions are used to evaluate the energy balance during these events and to quantify the associated dissipated power and released energy. A fraction of the energy released during reconnection events is involved in ion heating, as estimated by the energy distribution function of neutral atoms, a rather interesting feature in a reactorial perspective.

Reconnection events in high current reversed field pinch plasmas are often associated to the partial or total transitions from a helical topology with conserved flux surfaces to a configuration characterized by a chaotic magnetic field. The electron temperature dynamic together with the magnetic energy reconstructions are used to evaluate the energy balance during these events and to quantify the associated dissipated power and released energy. A fraction of the energy released during reconnection events is involved in ion heating, as estimated by the energy distribution function of neutral atoms, a rather interesting feature in a reactorial perspective.