Alfvén

Hannes Olof Gösta Alfvén (1908–1995) was a Swedish physicist who laid the foundations of magnetohydrodynamics (MHD) and plasma physics. His work on the behavior of conducting fluids in magnetic fields and the dynamics of plasmas earned him the Nobel Prize in Physics in 1970.

Alfvén is best known for identifying and describing Alfvén waves, a type of transverse wave that propagates along magnetic field lines in a magnetized plasma. These waves arise from magnetic tension forces and are a fundamental mode of motion in astrophysical and space plasmas. The characteristic speed of an Alfvén wave, the Alfvén speed, is v_A = B / sqrt(μ0 ρ), where B is the magnetic field, μ0 is the vacuum permeability, and ρ is the mass density. Alfvén showed that plasmas can support a variety of wave modes and instabilities, a framework that underpins much of space and solar physics today.

In his career, Alfvén held academic positions in Sweden and produced influential work and teaching in cosmical physics and plasma physics. His research encompassed the solar wind, cosmic rays, and interplanetary and interstellar plasmas, applying MHD to describe large-scale astrophysical processes. In addition to his Nobel Prize, he helped establish magnetized plasma physics as a central field in both theoretical and observational studies.

Alfvén’s legacy endures in modern plasma physics, fusion research, and space science. The concepts of Alfvén waves and Alfvén speed remain essential tools for interpreting measurements from the solar wind, planetary magnetospheres, and the broader cosmos, shaping how scientists understand the dynamics of magnetized plasmas.