A long, straight accelerator for smashing lighter-mass particles
Undetermined (possibly in Japan)
19 miles long
: Electrons and positrons
Protons aren't the only particles worth smashing, but they have their advantages, the most critical being mass. The more massive a particle, the less it radiates when it's being accelerated. For a large ring collider like the LHC, it's very difficult to accelerate lower-mass particles like electrons effectively because each time around the ring they radiate roughly four percent of their energy. Given that particle acceleration and collision happens at extremely high velocities, it's easy enough to see how an electron could very quickly lose most of its energy while circling the loop--even a 17-mile one.
If you want to smash electrons, then, you build a linear collider--a straight pipe with a particle accelerator at either end, through which you send electrons and positrons hurtling toward each other (and toward mutual destruction). This way the particles don't lose most of their energy while looping the accelerator ring. But there are other disadvantages to take into account.
First, linear colliders have to accelerate these particles to very high speeds over relatively short distances--the proposed International Linear Collider
is roughly 19 miles from end to end, so from end to collision point in the middle is half that--and that requires a lot of energy up front. Then, when only a fraction of the electron-positron pairs collide, the unused accelerated particles can't go around the loop again and try for a second collision. They are wasted, discarded, and the whole energy-intensive process starts over again. All said, it's less efficient than a proton collider. Yet the ILC is one of the clear favorites within the physics community right now and it or something like it could very well be world's the next big science experiment.
âTechnically, such an accelerator is likely feasible,â Wyatt says. âThe problem is, it will cost many billions of whatever currency unit you like to think in.â