A particle accelerator is a machine that speeds up charged particles, such as electrons or protons, to very high energies. Physicists then smash them into a target or into each other and study what comes out. This is how we test the Standard Model, discover new particles and look deep into the structure of matter.
Every accelerator uses the same two ideas.
Electric fields speed the particles up, because a charge in an electric field feels a force.
Magnetic fields steer them, because a moving charge in a magnetic field is pushed sideways, so it follows a curved path.
A linear accelerator sends the particles along a straight line. A circular accelerator bends the beam around so that the same electric fields can boost it again and again.
In this lesson we look at how two circular designs work: the cyclotron and the synchrotron. The biggest of them all is the Large Hadron Collider at CERN, a ring 27 km around.
The cyclotron
A cyclotron accelerates charged particles in a spiral inside two hollow D-shaped metal boxes, called dees, placed between the poles of a large electromagnet.
The magnetic field bends the particles into a semicircle inside each dee, and an alternating voltage across the gap between the dees gives them a push every time they cross it. As they speed up, they spiral outwards. Ernest Lawrence built the first ones in the 1930s.
The synchrotron
In a synchrotron, particles travel around a ring of fixed size inside a vacuum pipe.
Bending magnets keep the beam on the circle, and radio-frequency cavities give it a boost on every lap. As the particles gain energy, the magnetic field is increased in step, or synchronised, so the particles stay on the same path. This lets synchrotrons reach far higher energies than cyclotrons.
Applications
This video is a examines the workings of a cyclotron.
Although now decommissioned, this was the cyclotron, based in Sydney, involved in medical reseacrh,
In 2019, I had the opportunity to spend two weeks at CERN. This video gives you a brief overview of the what CERN is and what happens there.