1.) There are two major kinds of accelerators: linear and circular accelerators. The first ones use "only" electronic field (radio frequencies) the second ones combine them with magnetic fields. The most advanced ones can give the Energy of 7 TeV to the particles. The problem with linear accelerator is the fact that they reach their limits: the particles only go through them once and they cannot have infinite length. On the other hand, the circular accelerator has the advantage of accelerating them every time they go through the given part of the circle.