This machine, called the cyclotron, revolutionized accelerator physics. In 1932, Lawrence’s research group completed a 1.2 million eV (1.2 MeV) cyclotron. Almost all consecutive accelerators used for protons or nuclei rely on Lawrence’s concept of incrementally accelerating particles as they circulate in a ring or spiral.

As the energies of cyclotrons increased, the nice relationship that allowed for the constant round-trip time started becoming invalid. The reason is that Albert Einstein’s theory of special relativity demands that nothing can go faster than the speed of light. If a particle that is already moving close to the speed of light is pushed to a higher energy, only some of that energy will go into accelerating the particle, while the remainder goes into effectively increasing the particle’s mass, which itself is energy (yes, by E = mc² .) This effective mass-increase messes up the nice mathematics that gave us the constant round-trip time. Therefore, to counteract this effect, more powerful cyclotrons had to adjust the frequency of the accelerating voltage to account for the effective mass increase. Such machines, called frequency-synchronized cyclotrons (or synchrocyclotrons), allowed the transition to the gi

Figure 3: Higher energies are required to probe smaller structures. These energies range from every-day energies of about 0.1eV, which are required to break molecular bonds (e.g., digesting food), to energies that are reached only by rare cosmic rays and particles energized in advanced accelerators.

ant, much more powerful synchrotron accelerators that were to come. One of the early powerful synchrocyclotrons was erected at Berkeley in 1946 and achieved 350 MeV (million eV).