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GeV Acceleration In 3 Centimeters
ZonkerWilliam writes, "Here is a very interesting article, for the scientific community at least, on an advancement in laser wakefield particle accelerators. Being able to accelerate electrons to 1 Gev in the space of 3.3 cm calls up visions of portable devices that can be used anywhere: think of portable cancer therapies, if they can do the same for positrons, portable PET scans, possible use in compact fusion devices, capturing the dearly departed, etc. The uses are mind boggling." From the article: "By comparison, SLAC, the Stanford Linear Accelerator Center, boosts electrons to 50 GeV over a distance of two miles... The Berkeley Lab group and their Oxford collaborators... achieve a 50th of SLAC's beam energy in just one-100,000th of SLAC's length." I doubt that this tech will fit on a table top anytime soon. The article quotes the Berkeley researcher: "We believe we can [get to 10 GB] with an accelerator less than a meter long — although we'll probably need 30 meters' worth of laser path."
Seeing as how the LHC produces two beams in opposite directions with energy 7 Tev each (total collision energy is 14 Tev) this accelerator has 3 or 4 orders of magnitude to scale before it can even begin to compete with the LHC.
History will be kind to me, for I intend to write it - Sir Winston Churchill
GeV = giga electron Volts
Also, TFA links to an illustrated version of the story.
We're talking about electron volts. You see, electricity is not the electrons themselves, but rather a wave of energy passing from one electron to the next as they collide with each other. (A bit simplified, but hey.)
You know those desk decorations that have about 5 metal ball suspended from wires? If you lift one and let go, gravity imparts energy on one of those balls. When it hits the next ball, it transfers energy to the other ball, which in turn hits the next ball, transfers its energy, so on and so forth. When the last ball has nothing more to hit, it swings out from the kinetic energy imparted on it. This is pretty much how electricity works.
An electron Volt is a method of measuring the kinetic energy for individual particles. It translates directly to the voltage/joules calculations we all know and love, except that it only involves one particle instead of a wire full of them. Most commonly, this term is used in particle physics where the energy of a single particle matters.
What has been built here is a micro particle-accelerator capable of imparting massive velocities on individual electrons. This is useful for things like advanced medical scanners which bombard a target with a small number of high energy particles in order to get 3D image of the object. With a small enough particle accelerator, we could begin building devices like the medical tricorders you see in Star Trek. That's never been possible before.
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I actually do some research in this area (Plasma-wakefield particle acceleration, really really similar), and one of the biggest problems is getting the pulse-width incredibly small. They have to use something called Chirp Pulse Amplification and I think the beam length is somewhere on the order of 1-2 picoseconds. From the article, the power delivered by this beam is about 40 TeraWatts, which gives you some sort of idea. The acceleration gradient might be really high, but that doesnt mean youre going to get a desktop version any time soon. The equipment necessary to get the timing (pulse-length and power) right is incredibly difficult and expensive at the moment.
I'm perfect in every way, except for my humility.
For anyone who's interested, the actual velocity of the electrons is about 0.999999869 times the speed of light -- which is why talking about GeV is more instructive than talking about how fast the particle goes. The math follows, if you're interested.
... or you can type sqrt(1-1/(1GeV / electron mass / c^2)^2) into Google Calculator.
1GeV = energy = gamma * m * c^2 (gamma = 1/sqrt(1-v^2/c^2))
1 GeV / c^2 / m = gamma
1957 = gamma = 1/sqrt(1-v^2/c^2)
v/c = 0.999999869
Interesting fact: we usually hear about E = mc^2. That's the direct matter->energy conversion when the matter is at rest: if the matter is moving, we add on a factor of "gamma" -- which, at small velocities, is about 1 + 1/2 * v^2/c^2 (giving E = mc^2 + 1/2 mv^2, or rest mass + classical kinetic energy!)
It is not for electron beams that this would be a boon. It is rather for other particles (protons, heavy ions). The footprint of such facilities is pretty large. In the US there are currently a number of proton treatment centers. Protons allow you to generate more conformal treatments (e.g. treating tumor not healthy tissue) with very low levels of doses elsewhere in the body. The latter is important for patients expected to have long survival times (these are becoming more prevalent as we are able to cure more and more tumors with less side effects). This is particularly important in treatment of childhood cancers.
Heavy Ions is another ball game. Now you need a synchrotron to get these up to the desired energies. This means building another building only to hold the accelerator (no talk about treatment rooms, rotatable gantries or anything). Heavy ions are very good at destroying cells as they generate a high density of ionizations along their path. They also have the same interesting conformal properties as protons. There are only about 4 or 5 heavy ion facilities in the world, most of them in Japan or Europe. There currently is no economic gain to be made building heavy ion facilities, protons are now reimbursed and facilities are starting to be generated although they are very costly ($100 10^6)
A "portable" accelerator would reduce footprint and building costs immensely making it economically feasible. Unfortunately, the accelerators presented here do not have a high enough flux yet to be used for clinically relevant doses.
In short: interesting, but don't hold your breath. Implementation, even in a research setting is at least 10-15 years down the line. Of course I could be completely wrong and have one on my doorstep tomorrow, with a note by a physician, "please calibrate, a patient starts tomorrow"PET scans don't use accelerated positrons. A radioisotope is injected into the patient, which emits a positron when it decays. The positron immediately annihilates with an electron and emits two gamma rays. The gamma rays are detected and used to build the scan. To make the radioisotope you need a proton accelerator, but these are already very compact at 2-3m diameter, and anyway don't need to be near the patient.
Fusion, of course, has nothing to do with accelerating electrons.
I thought geeks knew this stuff, or do they only need to pretend these days?