What Is a Proton Accelerator?

An electric field accelerates a charged particle, such as a proton, and it collides with a target.

The idea behind a a proton accelerator is to fire billions of protons at billions of other protons and see what happens when the particles collide. Scientists look at the debris resulting from the collision to see if they can find any new types of particles.

The Device

A proton accelerator uses electric fields to propel charged particles called ions to extremely fast speeds and focus them in well-defined beams. An accelerator takes a particle such as a proton or an electron and speeds it up with electromagnetic fields, then smashes the particle into a target or a stream of other particles. At the point of the collision are detectors that record the results of the collision.
Protons can be collected by ionizing hydrogen gas. A hydrogen atom consists of one proton (with a positive charge) and one electron (with a negative charge) and is easily ionized by stripping off the electrons. The resulting proton stream will be positively charged.

Electric Fields and Magnets

The main power source for accelerating protons is powerful electric fields. In a field, the positively charged protons head for the negative potential. As soon as they get to the first one, another one is turned on downstream and they rush to that one and then to the next one further along. Scientists modulate the electric fields so that the particles continuously speed up until they're going at the desired speed.

The magnets steer the particle beam and focus it. A particle beam is a stream of accelerated ions (protons). The more protons in the beam and the more concentrated the beam, the better the chance that the resulting collision will be successful in producing new particles.

Accelerating the Protons

The protons require electric fields and magnets for acceleration and lots of room to build up speed. Scientists set up the collisions in two ways. In a fixed target collision, the proton beam is aimed at a fixed target that does not move. In a colliding beams collision, two proton beams are aimed at each other so that the beams intersect as they cross. Particle accelerators are built in two forms. They might be linear where the protons are accelerated in a straight line, or they might be circular as the Large Hadron Collider (LHC) at CERN.

Linear Accelerators

Linear accelerators send protons down a long, copper tube in a vacuum. Electromagnets focus the protons in a narrow beam and when the proton beam hits the target at the end of the tunnel, detectors record the subatomic particles and radiation released from the impact. The Stanford Linear Accelerator (SLAC) in California is almost two miles long.

Circular Accelerators

Circular accelerators propel the protons around a circular track over and over again. As the beam passes the magnets, the magnetic field is strengthened so that the beam accelerates with each pass. When the desired energy level is reached, a target is placed in the beam's path and detectors analyze the residual debris of the collision. The advantage is that the particle can save space and hardware as it circles. The disadvantage is that these accelerators emit electromagnetic radiation and energy must be expended continuously to keep the beam on path. So these accelerators are less efficient and the large accelerators must be buried underground to contain the radiation and maintain safety standards. The Fermilab accelerator in Illinois is 4 miles in circumference.

Particle Accelerators

Example of particle accelerators include: Cornell Electron Storage Ring (CESR), Stanford Linear Accelerator Center (SLAC), Deutsches Elektronen-Synchrotron (DESY), Fermi National Accelerator Laboratory (Fermilab), and European Organization for Nuclear Research (CERN).

References

• MIT Engineering: How A Proton Accelerator Works
• CERN Particle Accelerator: European Organization For Nuclear Research
• Lawrence Berkeley National Lab: General Particle Accelerator Reference

Resources

• Fermilab's General Accelerators: General Reference