3mm Inexpensive Chip Revolutionizes Electron Accelerators 113
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."
Re:More like Gamma-ray devices (Score:5, Informative)
"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.
Re:Or, another option (Score:4, Informative)
Re:More like Gamma-ray devices (Score:5, Informative)
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.
Re:More like Gamma-ray devices (Score:5, Informative)
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 [answers.com]
Re:More like Gamma-ray devices (Score:3, Informative)
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.
Re:More like Gamma-ray devices (Score:2, Informative)
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).
Re:Foreseeable effects? (Score:2, Informative)
It might enable radars of similar size, cheap enough to mount in every air vent in your house and able to direct the chilled air at people; combined with similarly miniaturized heat sensors, you'll find yourself cooling off or warming up much more quickly after coming inside.
Re:More like Gamma-ray devices (Score:3, Informative)
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!"
Re:so we wasted a shit load of money on colliders? (Score:5, Informative)
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.