M1 Linear Accelerator (Linac)

Topic

A linear accelerator, or linac, applies the radio-frequency acceleration mechanism described earlier in this catalog along a single straight path, passing particles just once through a long sequence of resonant cavities arranged in succession. The final energy achieved is essentially the sum of the increments provided by each accelerating structure traversed; consequently, reaching very high energies requires either highly efficient individual structures, a physically very long linac, or both. The primary advantage of this linear geometry is that it completely avoids the energy loss due to synchrotron radiation—a phenomenon previously identified in this catalog as dominant in curved paths—making the linac the only practical option for accelerating electrons to extreme energies without that radiation consuming all the energy supplied by the radio-frequency system. The trade-off is that each accelerating structure is used only once per particle—unlike in a ring, where the same set of cavities accelerates the particle during each of its many revolutions—meaning a linac typically requires far more installed radio-frequency infrastructure to achieve a given final energy. Linacs serve two distinct roles: as injectors, providing the initial energy boost to a beam that will subsequently continue into circular machines—a role explored later in this catalog—or as standalone accelerators delivering the final energy, whether for single-beam applications or as part of a future electron-positron collider. Thus, this module—which begins by discussing radio-frequency acceleration along a straight line—concludes by demonstrating that this very linearity, while demanding in terms of infrastructure, is precisely what avoids the energy penalty imposed by curvature in any circular machine.

ID:4961