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3mm Inexpensive Chip Revolutionizes Electron Accelerators
AaronW writes "Scientists and engineers at the US DOE SLAC National Accelerator Laboratory and Stanford University have developed an advanced accelerator technology smaller than a grain of rice. It is currently accelerating electrons at 300 million volts per meter with a goal of achieving 1 billion EV per meter. It could do in 100 feet what the SLAC linear accelerator does in two miles and could achieve a million more electron pulses per second. This could lead to more compact accelerators and X-ray devices."
"300 Mev photons are high-power gamma rays, not x-rays."
No, an accelerator of 300 MeV per meter over 3 mm gives you 1 MeV, or less if the actual field is over less than the chip size. Tuning down from there will easily get you into the x ray domain.
Avantslash: low-bandwidth mobile slashdot.
1 billion EV per meter is not going to cut it. Everyone knows you need 1.21 Gigawatts...
Exactly! Just look at the powerful computers we have right now. We clearly shouldn't have wasted all the money on mechanical and tube computers and just waited until we got i7s. In fact, fuck it; let's stop all investment now and wait another fifty years when we'll have 512-core pocket computers.
This is a reference to a movie called "Back to the Future"..
Fair enough, just two questions:
1) An electron hitting an atom will produce photons with the same energy via the Bremsstrahlung effect. As electrons will hit atoms sometimes, 300 MeV electrons means you will have 300 MeV photons, right?
2) How much energy a photon needs to transmute an atom? I believe it's lower than 300 MeV (but as a commenter said, it's 300 MeV *per meter* so really you need a lot of those devices chained together for them to become dangerous, I guess)
1) You'll probably get some photons out of the deal but they won't all be 300MeV. There are lots of places to put energy (this is what makes particle physics hard) and photons are only one of those places. See the light-matter interaction box on the "Photoelectric_effect" wiki page. At 1MeV, even pair production becomes viable.
2) Photons don't transmute atoms (search for "photonuclear reactions" for the exceptions). Neither do electrons (look up "Electron_capture" for the exception, but it generally only happens with electrons already bound to the nucleus rather than ones flying around). Neutrons transmute elements because they can ignore the Coulomb barrier. Irradiating, say, rubber tubing with gamma radiation won't make it radioactive (it'll probably make some radicals and mess with the chemistry, but nothing nuclear). Neutron radiation is a totally different story.
The modern classification of x-ray vs. gamma-ray is based on the source of the emission (electron vs. nucleus), not the wavelength. http://wiki.answers.com/Q/What_is_the_difference_between_gamma_rays_and_X-rays
1. This accelerator, like SLAC (in it's current configuration), accelerates electrons, and the accelerated electrons are undulated (wiggled) in a vacuum to produce xrays (photons), then the electron beam is deflected off-line into a beam absorber, nearly all of the beam energy at SLAC is discarded, rather than reaching the experimental target. This is unlike most xray sources which generate xrays by spallation (collision with atoms), as the energy (wavelength) of the photons has the same bandwidth as the particle bunch, rather than being spread over a large bandwidth as they are in a typical LINAC xray source. The radiation mechanism is the same as in a synchrotron, when an electron is accelerated it emits EM radiation, because it is being cyclically accelerated by alternately poled magnets, the emitted radiation wavelength is determined by the beam velocity, the spacing of the undulators, and relativistic time dilation, rather than the beam energy (the X-ray photons have lower eV than the electrons).
2. A neutron has a rest mass of 939.565378 MeV/c2, but I'm not aware of any experimental validation of gamma transmutation.
These new devices only accelerate electrons. For high energy physics research other particles need to be accelerated and collided, e,g, hadrons (hence the name Large Hadron Collider) It's unclear if the same tech can be used for other particles. Rubbish TFA.
assignment != equality != identity
There are photoneutrons. If I recall correctly they are typically produced by high energy photons hitting deuterium. The neutron produced can go an activate material around it. For a nuclear reactor that has shut down, photoneutrons are the dominant form of source neutrons produced for a little while (the gammas come from beta decay which drops off over time).
Those units don't even have the same dimension, how do you propose to compare them?
1 Watt is a Joule per second. An eV is 1.6*10^-16 Joule. Now according to the theory of relativity, space and time are just different dimensions of the space time, therefore space units and time units are related. The factor is the light speed, 3*10^8 m/s, that is, a second is 3*10^8 meters, or a meter is 1/(3*10^8) seconds
Therefore 1 eV per meter is 1.6*10^-16 Joule * 3*10^8/second, or 4.8*10^-8 Joule/second. Now a Watt is 1 Joule/second, therefore 1 eV/m is 4.8*10^-8 Watt.
On the other hand, 1.21 Gigawatt are 1.21*10^9 Watt. Which is a factor of about 2.5*10^16. So still quite a way to go for time travel.
SCNR ;-)
And in order to not confuse anyone: the calculation above is of course meaningless because even though you can make the *units* the same using relativity, the *quantities* are still completely different; just like the torsional moment has the same unit as energy, but certainly is not the same as energy.
Ahh didn't see it was 300 Mev *per meter*. Small detail, thanks!
This masterful demonstration of The Save reminds me of the way a cat lands on its feet no matter how it is thro^H^H^H^H^H^H^Hfalls.
..Mullah or Pope, Preacher or Poet, who was it wrote: "Give any one species too much rope and they'll fuck it up"?
Those units don't even have the same dimension, how do you propose to compare them?
Very carefully?
Ezekiel 23:20
Well, yes and no, it also depends on the field what term is used. Astronomers always name it gamma radiation, while physicists from the field of elementary particles and accelerators use the term gamma radiation only for radiation coming from the nucleus. X-ray radiation is used to specify the wavelength range, for any other source.
The SLAC isn't a spallation radiation instrument. It produces xrays by coherent synchrotron radiation: as the electron beam passes through the end-stage undulators, the electrons are undulated at a fixed wavelength by a series of alternating undulator magnets, the wavelength of which is shorter (higher energy) than that of the spacing of the undulators because the electrons "see" the undulators as closer together due to time dilation, the electrons, still carrying over 99% of the bunch energy are then diverted into a dump load, which absorbs the energy of the beam. The xrays, being uncharged photons, carry on past the bending magnet at the end of the accelerator line and into the target huts in the experimental lab.
Because the photons are moving with the electrons during the stimulation stage, they pile up and interact with the electron bunch to produce more photon emission at a very narrow band gap, hence why it is called a free-electron laser.
I'm talking about the SLAC, because this new chip accelerator, besides being developed at SLAC, is intended to be used as an electron source for a similar design of FEL. I suppose it could also be used for high energy spallation experiments, where it would generate much higher energy photons and other particles with a much higher conversion efficiency than a FEL, but with a broad spectrum, rather than the narrow line that an FEL (and until recently, only SLAC) is uniquely able to produce at xray and higher energies.
As a medical radiographer commented when I was talking to him about SLAC: "Cool, colored xrays!"
Give me an efficient source of neutron flux and I can stop collecting smoke detectors. I'm kidding obviously, but if this is cheaper than collecting radium watch hands we may soon have more "Nuclear boy scouts" on our hands.
On the plus side, not all neutron generators are polite enough to stop generating when you cut the power, so it might be an improvement.
Riiiiiight, because anyone in their right mind is gonna click a random link ending in .dmg... Aka, a Mac disk image file, commonly used for distributing software.
Hey, if you think that it's diseased, don't mount it. Did you skip sex ed or something?
If you read the article, you'll realize that there is a separate laser accelerator necessary BEFORE this chip, and then a second high-power IR laser necessary to drive the chip.
More-or-less, they've increased the efficiency of laser-based electron acceleration. Good on them, but the solution isn't, as the summary suggests by omission, just a small chip alone and nothing else.
More importantly for the parent (I know, I know, don't feed the trolls), the presented accelerator only accelerates electrons, and is intended as a gamma and x-ray source. That's very different from accelerating electrons and positrons to nearly the speed of light, or protons, or atomic nuclei, etc. To do high-energy physics, you need big, big accelerators. The device to accelerate a single subatomic particle to levels where it carries as much energy as a brick dropped on your foot, isn't going to be a crystal a few millimeters on a side.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
We didn't. Early computers were funded from commercial sources not taxation, and they had practical applications right from the start.
ENIAC was arguably the first general purpose electronic computer, and it was built for the US military (a wing of their government). Zuse's Z3 was arguably the first general purpose electric computer, and it was built for the German Air Ministry (a wing of their government). Of course, these devices are practical applications representing the culmination of centuries of prior basic research. The basics of electrical and electronic science was performed in the seventeenth and eighteenth centuries, largely by aristocrats who could be considered to be functionally the government of the day, many of whom supported their work with the labor of their tenants, which was pretty nearly taxation at the time. It wasn't until the nineteenth century that practical applications (notably the telegraph) began to appear. Even after the point where commercial interests began to involve themselves, taxation and government programs continued to support development of technologies like transistors, network communication technologies, and photolithography.
> "This could lead to more compact accelerators and X-ray devices."
...and weapons.
Actually yes. Luis Alvarez, a Nobel Prize winning experimentalist argued extensively that large grants make experimentalists lazy. He joked that Michelson-Morley today would be done by launching antipodal satellites with expensive laser alignment hardware at the very low cost of $300 million.
At least, it won't scale in the way the article suggests.
It's possible that the tech involved might make for a more efficient acceleration mechanism than the current superconducting electromagnets, but I sincerely doubt it will lead to significantly smaller accelerators: accelerators are large not because it isn't possible to accelerate the electrons in a shorter distance, but because it's extremely inefficient to do so.
Large accelerators are limited by the fact that rapid accelerations of charged particles cause lots of radiation to be emitted. The amount of radiation emitted increases dramatically as the particles approach the speed of light, making it harder and harder to push the particles faster (or even just to keep them going at speed in a ring for circular accelerators). Even if this mechanism of electron acceleration is a hundred-fold more efficient energetically than the SLAC accelerator, it still couldn't accelerate electrons to SLAC speeds in 100 feet, because it would need vastly higher acceleration and that higher acceleration would lead to lots of radiation, limiting the pace of acceleration. Personally, I doubt it's 100 times more efficient. I bet most of that efficiency difference comes from this small device not operating on electrons moving anywhere near the speed of light.