The discovery of synchrotron radiation

Thirty-five years ago the electromagnetic radiation that results from the acceleration of electrons in a circular accelerator was observed for the first time in a 70-MeV synchrotron at the General Electric Research Laboratory in Schenectady, NY. In May 1981, an entire issue of Physics Today was devoted to synchrotron radiation, which is widely recognized as an important research tool for physicists, chemists, and biologists and perhaps in medicine as higher-energy synchrotrons and electron storage rings have been constructed. It seems timely to review the background of its discovery at this laboratory and to record the exact circumstances of the first visual observation and measurements of the radiation. Before discussing the first observation of synchrotron radiation from a laboratory machine it should be noted that for centuries man had been seeing synchrotron radiation from stars or galaxies without knowing that some of their light resulted from the acceleration of elementary particles in the large magnetic fields associated with astronomical objects. In 1898 Lienard' first pointed out that an electric charge moving in a circular path should radiate energy and he calculated the rate of radiation from the centripetal acceleration of an electron. The theory was extended subsequently by Schott,^ who received the Adams Prize in 1908 at Cambridge University for his essay, "The Radiation from Electric Systems or Ions in Accelerated Motion and the Mechanical Reactions on their Motion which Arise from I t . " Schott, attempting to provide the background for an electron theory of matter, calculated the amount and the angular distribution of radiation from relativistic electrons grouped in various ways in orbits of proposed atomic models.