Research fields
Superconducting magnets
Fundamental plasma physicsFundamental plasma physics
The group's activities on fundamental plasma physics cover:
- Magnetic Reconnection: magnetic reconnection is believed to be a crucial mechanism in order to explain different phenomena in laboratory as well as in astrophysical plasmas. Sawtooth oscillations and solar flares are examples of such phenomena. Although magnetic reconnection is a local process, occurring on a small scale, its main feature is a rearrangement of the magnetic field lines topology on a global scale. Typically in 2D a magnetic island forms together with vorticity and current density layers. Related to these layers, strong shear flows may develop and, under appropriate conditions, become unstable to a hydrodynamical instability of the Kelvin-Helmholtz type, generating turbulent structures on small scales.
- Magnetic Island Control: the magnetic island, generated by a reconnection process, are a serious cause of degradation of plasma confinement in the Tokamak devices. An important open issue is to find appropriate means for the control of such instabilities. One of the most promising methods suitable to counteract robustly the tearing instabilities in a Tokamak is based on the injection of an Electron Cyclotron Current Drive (ECCD), that can be effectively simulated by the localized deposition of an external control current within the magnetic island.
- Magnetic Chaos: for reconnection processes that are nearly two dimensional, 3D effects are of interest in that they introduce regions of magnetic field line stochasticity centered around the separatrices of 2D magnetic islands, where current and vorticity sheets are localized. During this phase, regions of regular and irregular magnetic fields coexist and coherent structures that form barriers to the transport of the magnetic field line may exist.
- Runaway Electrons: in tokamak disruptions the Ohmic current is often replaced by a current of runaway electrons, which is likely to be more peaked in the center of the discharge than the pre-disruption current. This raises the question of the stability of the post-disruption plasma, where the equilibrium current is entirely carried by the runaway electrons while the cold background plasma is relatively resistive.
- Turbulence: the problem of the mutual interaction between fluid and magnetic instabilities in hot and rarefied plasmas, is relevant in tokamak plasmas, due to its implications on the transport mechanisms. Indeed the coexistence of structures associated with magnetic instabilities and fluid turbulence is crucial for controlling the stability of the fusion plasmas.
- Transport of impurities in Tokamaks and its interaction with magnetic islands: the use of tungsten in plasma facing components in fusion devices is considered a solution for the problems of heat load on the walls and of Tritium retention. However, Tungsten is a heavy metal prone to pollute the discharge. Moreover, in some discharges it accumulates in the plasma core, leading to radiation collapse and possibly disruption, and this accumulation seems exacerbated by the presence of a magnetic island.