Thursday, February 11, 2016

This Educational Video on Accelerators Doesn't Get It

OK, before you send me hate mail and comments, I KNOW that I'm hard on this guy. He was probably trying to make a sincere and honest effort to explain something based on what he knew. And besides, this video is from 2009 and maybe he has understood a lot more since then.

But still, this video is online, and someone pointed this out to me. I get a lot of these kinds of "references" from folks online, especially with Wikipedia entries. And try as I might to ignore most of these things, they ARE out there, and some of these sources do have not only misleading information, but also outright wrong information.

This video, made presumably by a high-school science teacher, tries to explain what a particle accelerator is. Unfortunately, he described what a particle accelerator CAN do (i.e. use it in high energy physics colliders), but completely neglected the description of a "particle accelerator". This is a common error because most people associate particle accelerator with high energy physics, and think that they are one and the same.

They are not!

As I've stated in an earlier post, more than 95% of particle accelerators on earth has NOTHING to do with high energy physics. One of these things might even be in your doctors office, to generate x-rays to look at your insides. So using high energy physics experiment to explain what a particle accelerator is is like using creme brulee to describe what a dessert is. Sure, it can be a dessert, but it is such a small, SMALL part of a dessert.

A particle accelerator  is, to put it bluntly, a device to accelerate particles! Period. Once they are accelerated, the charge particles can then be used for whatever they are needed for.

Now, that may sounds trivial to you, but I can assure you that it isn't. Not only does one need to accelerate the charge particles to a set energy, but in some cases, the "quality" of the accelerated particles must be of a certain standard. Case in point is a quantity called "emittance". If these are electrons, and they are to be used to generate light in a free-electron laser, then the required emittance, especially the transverse emittance, can extremely low (in fact, the lower the better). This is where the study of beam physics is crucial (which is a part of accelerator physics).

The point I'm trying to make here is that the word "particle accelerator" is pretty generic and quite independent of "high energy physics" or "particle collider". Many accelerators don't even collide these particles as part of its operation (in fact, many do NOT want these particles to collide, such as in synchrotron radiation facilities).

What this teacher neglected to describe is HOW a particle accelerator works. The idea that there are these accelerating structures with a wide range of geometries, and they can have either static electric field, or oscillating electric field insides of these structures, that are responsible for accelerating these charged particles, be it electrons, protons, positrons, antiprotons, heavy nucleus, etc... And even for high energy physics experiments, they don't usually collide with a "fixed" target, as implied in the video. Both LEP, the Tevatron, the LHC, etc. all collide with beams moving in the opposite direction. The proposed International Linear Collider is a linear accelerator that will collide positrons and electrons moving toward each other in opposite direction.

So while the intention of this video is noble, unfortunately, the information content is suspect, and it missed its target completely. It does not really explain what a particle accelerator really is, merely what it can be used for. It also perpetuates the fallacy that particle accelerators are only for these exotic experiments, when they are definitely not.


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