Beginning in about 1945, improved circular particle accelerators were made. In them, magnetic fields were used to confine and control the position of the particle beams. Electric fields are used repeatedly for accelerating purposes.
Scientists then discovered that by accelerating known particles, such as protons, to very high speed and causing them to collide with other protons, many new particles were produced.
These particles were almost always very unstable with incredibly small half-lives. Over 400 unstable temporary particles have been found.
The aerial photograph above is of the accelerator centre in CERN in Switzerland. The smaller accelerator has a circumference of 7 km, the larger one 27 km. The tunnels for both accelerators are underground.