It is fairly easy to obtain particles.
Physicists get electrons by heating metals;
they get protons by robbing hydrogen of its electron; etc.
Accelerators speed up charged particles by
creating large electric fields which attract or repel the particles.
This field is then moved down the accelerator, "pushing" the particles along.
In a linear accelerator the field is due to traveling electromagnetic
(E-M) waves. When an E-M wave hits a bunch of particles, those in the back
get the biggest boost, while those in the front get less of a boost. In this
fashion, the particles "ride" the front of the
E-M wave like a bunch of surfers.
The next page shows this process in an easier to understand