Density limit in fusion plasmas

It is widely accepted that plasmas magnetically confined in tokamak configuration have an upper density limit, called Greenwald limit. This limit is expressed by the formula n (10²⁰ m^-3) < I_p (MA)/S (m²), where n is the average plasma density, I_p is the plasma current and S is the area of the vacuum chamber cross section. This is a hard limit, in the sense that going beyond it triggers a catastrophic squence of events, called disruption, which causes the loss of the plasma. The Greenwald limit has been obtained empirically, putting together data coming from many different experiments, and has no theoretical explanation.

The aim of this line of activity, carried out with a group from the Department of Mathematics at the University of Milano, is to give an expression for the density limits in tokamaks (and subsequently also in other configurations) starting from the first principles of electromagnetism.

Essential bibliography

M. Zuin, A. Carati, M. Marino, E. Martines, L. Galgani, A first principles explanation for the density limit in magnetized plasmas, preprint.

M. Marino, M. Zuin, A. Carati, E. Martines, L. Galgani, Short-wavelength oscillatory modes in a magnetized neutral plasma, and theoretical derivation of a density limit, preprint.