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Hannes Alfvén was a Swedish plasma physicist who won the Nobel Prize in Physics in 1970. He is best known for his work on magnetohydrodynamics, the study of the interaction of magnetic fields and plasmas. Alfvén's work on magnetohydrodynamics helped to explain the behavior of plasmas in stars and other astrophysical objects, and it has also been used to develop new technologies, such as fusion power plants.