Alfvénic

Alfvénic describes fluctuations or waves in a magnetized plasma that behave like Alfvén waves. It is named after Hannes Alfvén, who described these transverse, incompressible disturbances and received the Nobel Prize in Physics in 1970 for work on magnetohydrodynamics.

In an ideal, incompressible magnetohydrodynamic (MHD) plasma, Alfvén waves propagate along the background magnetic field at the Alfvén speed v_A = B0 / sqrt(μ0 ρ), where B0 is the ambient magnetic field, μ0 the vacuum permeability, and ρ the mass density. The perturbations are transverse to B0, with the velocity fluctuation δv and magnetic-fluctuation δB tied by δv ≈ δB / sqrt(μ0 ρ). Because the restoring force is magnetic tension, Alfvén waves can carry energy and momentum along field lines without compressing the plasma to first order.

Alfvénic fluctuations are a key feature of many space and laboratory plasmas. They are commonly observed in the solar wind and planetary magnetospheres, and they are important in fusion devices and other laboratory plasmas. In turbulent plasmas, a state is often described as Alfvénic when velocity and magnetic-field fluctuations are highly correlated and the noncompressive, shear-Alfvén mode dominates, though real systems can exhibit weak compressive effects.

See also: Alfvén wave, magnetohydrodynamics, solar wind, space plasma physics, plasma turbulence.