M2 Synchrotron and Storage Ring

Topic

A synchrotron is a circular machine in which particles make many repeated orbits, passing time and again through the same set of magnets and radio-frequency cavities described in the fundamentals section, gaining energy in small increments with each pass. Unlike a cyclotron—an older circular machine where the orbital radius increases with energy—the radius in a synchrotron remains fixed: as the particle's energy rises, the dipole magnet field is increased synchronously to keep the particle on the same circular path, which is the origin of the machine's name. This process of gradually increasing the magnetic field alongside the beam energy is called "ramping," and its duration depends on the machine's size and how quickly its magnets can respond without generating eddy currents or—in the case of superconducting magnets—risking the loss of superconductivity, a vulnerability already noted in the fundamentals section. Once the machine reaches its nominal operating energy, it can function in storage-ring mode: the beam simply circulates stably for an extended period, while experiments utilize that circulating beam to collide it with another beam, extract it toward a fixed target, or harness the synchrotron radiation it continuously emits. Maintaining a stable circulating beam for hours—rather than just during the brief acceleration phase—depends critically on the vacuum quality described in the fundamentals section, precise beam optics correction, and keeping the betatron wavenumber away from the previously noted dangerous resonances. Thus, this module, which opens with a ramp that boosts energy with each successive orbit, concludes with the same ring maintaining—at its final energy—an equilibrium that relies on everything described in the fundamentals section.

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