FUTURE
 
Today, the limit is being reached for minimizing the energy losses to synchrotron radiation in circular accelerators; longer linear accelerators are being built instead. The International Linear Collider to be finished sometime around 2020, will be up to 30 or 40 km in length.
 
Another recent solution that has been proposed is using plasma in the beam cavities of the accelerators instead of a vaccuum. Pulses of electrons(or laser light) will follow the particles being accelerated. The particles in these pulses will disrupt the plasma, which causes a chain reaction as the plasma particles hit each other; together this pushes the particles even futher. This is called plasma wakefield acceleration.
 
As for future usages of large-scale particle accelerators, some think that according to superstring predictions, black holes might eventually be produced. Less far-fetched ideas include using particle accelerators to break down nuclear waste cleanly, and to produce clean energy safely. "Accelerator transmutation of waste" would take place by hitting the nuclear waste with particles until neutrons were released, at which point the neutrons and the radioactive parts would form a stable element.
 
Even more promising is the "energy amplifier" idea from Carlos Rubbia, in which accelerators could be used with nuclear reactors for safe energy production. The accelerators would cause nuclear fission by bombarding particles with protons. This would make nuclear reactors safer because it is not a self-sustaining reaction and would not get out of control like the chain reactions currently used in nuclear power plants.