The discovery of magnetohydrodynamic waves

The discovery of magnetohydrodynamic waves was a major breakthrough in plasma physics and its applications to space physics and fusion research. The waves were discovered by Hannes Alfvén and are therefore also called Alfvén Waves. The discovery was typical of Alfvén's outstanding ability to derive results of great generality from analysis of specific problems—in this case, the sunspots and the sunspot cycle. It was also typical of his electrodynamic approach to astrophysical problems. It took a long time before his discovery was generally accepted, partly because of the contemporary lack of means to verify the waves experimentally. The experimental verification of the magnetohydrodynamic waves came gradually many years later, beginning with experiments in liquid metals. It was not until the end of the 1950s that experiments were performed in plasmas. These clearly and conclusively demonstrated the existence and properties of magnetohydrodynamic waves, in excellent agreement with the theoretical prediction of Alfvén. The discovery of the magnetohydrodynamic waves opened a whole new field of physics—magnetohydrodynamics, which is of profound importance especially, but not only, in plasma physics. At the same time as the magnetohydrodynamic waves, Hannes Alfvén also discovered another magnetohydrodynamic concept, the frozen-in magnetic field.