Magnetic Reconnection in Plasmas

Non-diffusive transport of suprathermal ions in turbulent plasmas

10 Aug 2015, 12:00

25m

FD5 (FD5)

Invited Workshop, August 10-14 Pre-noon I

Speaker

Mr Ivo Furno (EPFL-CRPP)

Description

Suprathermal ions with energies greater than the background plasma species are frequently observed during magnetic reconnection in astrophysical and laboratory plasmas. Understanding the interaction between turbulence and suprathermal ions is a fundamental problem to shed light on the physics governing many plasma phenomena, from particle dropouts during impulsive solar energetic events to transport of alpha particles in fusion reactors. Advances are hampered by difficulties in diagnosing distant astrophysical plasmas as well as fusion-grade plasmas. We report on experimental, numerical and theoretical investigations in the laboratory device TORPEX, which permits full characterization of suprathermal ion dynamics and turbulent structures. TORPEX is a toroidal device in which turbulent structures are intermittently generated and propagate across a confining magnetic fields. Suprathermal ions are locally injected using a miniaturized source and detected using grid-energy analyzers. By combining unprecedented 3D measurements and first-principle numerical simulations, we show unambiguous evidence for the existence of sub-diffusive and super-diffusive suprathermal ion transport regimes. We identify the mechanisms responsible for the non-diffusive transport and show that the transport character is determined by the interaction of the ion orbits with the turbulent structures, and is strongly affected by the ratio of the ion energy to the background plasma temperature. Furthermore, time-resolved cross-field dynamics reveal that suprathermal ions experiencing super-diffusive transport are associated with bursty displacement events. This work links measurements usually inaccessible in fusion and astrophysical plasmas, namely energy resolved 3D time-averaged measurements, with Eulerian time-resolved measurements, which are often the only accessible ones in such systems.

Presentation materials

Slides

Nordita2015_Furno.pdf