Hannes Alfven. Portrait of Hannes Olof Gosta Alfven (1908-95), Swedish theoretical physicist. Alfven studied the physics of ionised gases or plasmas, especially their behaviour in electric and magnetic fields (magnetohydrodynamics). He theorised that magnetic fields passing through a plasma can bind the ions to the field lines. In 1942 he predicted the existence of Alfven waves in plasmas; these were later experimentally observed. Alfven's work led to important advances in the understanding of the movement of charged particles in the magnetic fields of the Earth and Sun and in the development of fusion reactors. He was awarded the 1970 Nobel physics prize.