Cornell scientists have researched the fundamental particles of nature for more than 70 years. Cornell physicists, such as Hans Bethe, contributed not only to the foundations of nuclear physics but also participated in the Manhattan Project. In the 1930s, Cornell built the second cyclotron in the United States. In the 1950s, Cornell physicists became the first to study synchrotron radiation. During the 1990s, the Cornell Electron Storage Ring, beneath Alumni Field, was the world's highest-luminosity electron-positron collider. After building the synchrotron at Cornell, Robert R. Wilson took a leave of absence to become the founding director of Fermilab, which involved designing and building the Tevatron, the largest accelerator in the United States. Cornell's accelerator and high-energy physics groups are involved in the design of the proposed International Linear Collider and plan to participate in its construction and operation. The International Linear Collider, to be completed in the late 2010s, will complement the Large Hadron Collider and shed light on questions such as the identity of dark matter and the existence of extra dimensions.