M7 Linear Collider

Topic

A linear collider smashes together two beams—typically of electrons and positrons—that have each been accelerated in their own linac (the same type of machine described at the start of this section) and aimed at one another, rather than circulating them in a shared ring. This architecture completely avoids the synchrotron radiation identified earlier as the dominant design factor for electrons, because each particle passes through the acceleration zone only once and never follows a sustained curved path; this makes it the only viable way to achieve electron-positron collisions at energies far exceeding those attainable in a circular ring of reasonable size. The trade-off is that, unlike a storage ring where the same beam collides repeatedly with every revolution, in a linear collider each bunch collides only once and is then discarded. This necessitates the generation of a continuous stream of high-quality new bunches—extremely compressed at the collision point—to achieve a collision density competitive with that of a circular ring. Achieving such extreme compression without the benefit of the multi-turn cooling techniques described earlier in this catalog requires electron and positron sources with extraordinarily low initial emittance and ultra-precise final-focus systems. An additional challenge inherent to this architecture is the disruption effect: when two very dense bunches of opposite charge cross paths, the intense electric field of the opposing bunch acts as an additional lens on the particles of the other bunch during the very instant of collision, curving their trajectories and slightly altering the available energy spectrum. Thus, this module—which opens by highlighting how the cost of curvature is avoided—concludes by showing that this saving comes at the price of having to produce, ceaselessly, a continuous stream of perfect bunches.

ID:4967