Spontaneous largescale momentum exchange by microinstabilities: An analogy between tokamaks and space plasmas

Based on a recent theory (Coppi, Nuclear Fusion, 42, 1, 2002) of spontaneous toroidal rotation in tokamaks (Lee et ai, Phys Rev Lett. 91, 205003. 2003) and in astrophysical accretion disks, we propose that an analogous process could be at play also in the Earth space environment. We use fully kinetic simulations to study the evolution of drift instabilities and we show that indeed a macroscopic velocity shear is generated spontaneously in the plasma. As in tokamaks, the microscopic fluctuations remain limited to the edge of the plasma channel but the momentum spreads over the whole macroscopic system.