Linear and Circular Accelerators

The Modern World of Particle Acceleration and Discovery

Mar 6, 2008

Particle Accelerators form an enormous part of physical discovery, and as such, they are constantly getting bigger, better, and (much) more expensive.

Within just the past few decades, particle accelerators have evolved a great deal since their initial, somewhat less-than-impressive predecessors (such as the use of “natural” particle accelerators in the form of Cosmic Rays, and the first man-made accelerator – the “Cyclotron”), and now tend to come in two main varieties.

Linear Accelerators

There is the linear type, which is the simplest to make, as it only requires one to create a perfectly straight beam of particles (such as in an electron-producing cathode ray). This beam is accelerated using finely-tuned magnetic fields of increasing power until the particles reache the end of the line (while it may sound simple, the immense precision required to perform this feat is wholly remarkable), interacting with some form of matter, these reactions thusly photographed in a bubble chamber.

While it may be simple in function, a good linear accelerator is really quite an enormously impressive piece of architecture. The great difficulty comes in the attempt to supplying the accelerator with enough energy to build up the speed necessary to smash particles together at the necessary energy levels. Most of the available power goes to powering the electromagnets, which have required more and more energy as the power of the accelerators have grown even grander over the years. Once all of this is all finished, the accelerator is turned on and the particles collide.

The longest linear accelerator in the world today is the 2 mile long SLAC (Stanford Linear Accelerator Center) in Menlo Park, CA – truly an unrecognized giant among modern-day architecture, especially considering the fact that it is an instrument of unbelievably high precision, built practically directly on top of the famous San Andreas fault (perhaps this was a strategic blunder, but it is impressive nonetheless).

Circular Accelerators

Other, even more impressive accelerators in existence today are of the circular sort; perhaps the most famous being Fermilab near Chicago with a four mile long proton-antiproton collider ring called the Tevatron, and the accelerator at CERN (The acronym originally stood for Conseil Europeen pour la Recherche Nucleaire, and while that name has since been set aside, the acronym remains), which is located in between Switzerland and France and has operated several state of the art accelerators since its inception, but will begin operation of its new Large Hadron Collider, a ring 17 miles in circumference in (hopefully) May of 2008.

The LHC is the most ambitious (and expensive, at almost $10 Billion) such project yet undertaken, and will hopefully be used to discover several new particles which have been theorized, yet for which scientists have not yet had the power necessary to create experimentally, such as a particularly elusive particle known as the Higgs Boson, which will hopefully help to explain mysteries about the some of the earliest moments of the universe. It is really quite exciting.

The benefit of a circular accelerator is that it possesses an infinite distance through which the beam may be accelerated – it can potentially keep a beam of particles (actually, while this is a common description of a particle accelerator, in reality, the particles are made to move through in “clumps” so as to make them more manageable, rather than as a continuous beam) moving through the same system forever, accelerating faster and faster (ebbing closer and closer to the speed of light) until there is no longer enough power to accelerate it any further.

One can imagine the fine-tuning necessary to accomplish such a task – with every lap the particles take around the accelerator, the system must, with absolutely perfect accuracy, slightly increase the power of the magnets to just such a degree that the orbit remains at exactly the same size – this must happen many times each second for the system to work. Speeds terribly close to the speed of light have been recorded in accelerators such as these – but of course that elusive speed has never, and will never be reached, thanks to Einstein's E = mc² equation, which says that the closer something gets to the speed of light, the harder it will be to push it any faster, hence the reason these machines take up so very much power, for such seemingly little gain in energy.

With excitement growing over the opening of the LHC, physicists’ mouths are watering to get a hold of the first bits of data that come streaming out of these new experiments. Who knows, an entirely new era of physics might be right at the doorstep!

Asimov, I. (1966). Understanding Physics: 3 Volumes in 1. Barnes and Noble Books.

Carrigan, R. A., & Trower, W. P. (1989). Scientific American: Particle Physics in the Cosmos. New York, NY: Scientific American.

Clay, R., & Dawson, B. (1997). Cosmic Bullets - High Energy Particles in Astrophysics. Australia: Helix Books.

Lederman, L. (1993). The God Particle: If the Universe is the Answer, What is the Question? New York: Dell Publishing.

The copyright of the article Linear and Circular Accelerators in Particle Physics is owned by Isaac M. McPhee. Permission to republish Linear and Circular Accelerators in print or online must be granted by the author in writing.