Laser pulses fired into hydrogen produces intense x-rays.Tom Tracy Photography / AlamyPosted on 10/01/2009 12:26:56 AM PDT by neverdem
Laser pulses fired into hydrogen produces intense x-rays.Tom Tracy Photography / AlamyA team of physicists has built a small, powerful X-ray source — a prototype of the sort of machine they hope could replace much larger facilities.
The technology has the potential to revolutionize everything from microbiology to materials science by giving scientists easier access to high-quality images of the things they are studying.
Researchers use X-rays to probe all manner of things — from comet dust to fossilized animals trapped in amber. But making high-quality images requires much brighter and better controlled sources than those available in most institutions. So at the moment, most scientists use large particle accelerators known as synchrotrons, which work by accelerating electrons around a ring. As the electrons bend along the circular path, they naturally emit high-quality X-ray radiation.
Synchrotrons are large, costly and usually in high-demand by scientists, so Matthias Fuchs of the Max-Planck-Institute for Quantum Optics in Garching, Germany, and his colleagues have been working on another way to generate electrons.
Rather than using conventional magnets to guide and accelerate electrons, the team used a powerful laser beam and a small cell of hydrogen gas. They shot a brief, 37-femtosecond (10-15 seconds) pulse into the cell to blow the electrons off the hydrogen atom's nuclei. But electrical attraction causes the electrons to snap back towards the positive ions, so for a brief period after the pulse the electrons vibrate back and forth around the hydrogen atom's positive core, producing a wave. As they do so, a few electrons break loose and ride the crest of the electron wave. "Just like a surfer, the electrons can surf down these waves," Fuchs says.
The electrons then sail through a series of magnetic lenses, which feed them into a second series of magnets that cause them to wiggle back and forth — releasing low-energy 18-nanometre wavelength X-rays as they go.
Because the electric fields between the hydrogen ions and their electrons are so large, the electrons pick up speed much more rapidly than they would in a conventional accelerator. That means a machine the size of a building can be shrunk to the size of a tabletop. Well, almost. Fuchs says that including the laser, the accelerator takes up two fairly large tables. "We came up with the phrase 'banquet tabletop'," he says. The team's research has been published by Nature Physics1.
Nevertheless, "it is exciting", says Tom Katsouleas, dean of engineering at Duke University in Durham, North Carolina. Other groups had already shown lower-power radiation from similar systems, so it wasn't surprising, he adds. "I don't think anybody really doubted it could be done." "But they've actually shown that the beam quality can be fairly high," he says.
Because relatively few electrons are accelerated, the pulses are bright but short, so the 'tabletop' accelerator is unlikely to replace conventional synchrotrons any time soon. Still, Katsouleas says, there is no reason, in principle, why they could not be made into a workable X-ray source for use in universities.
doi:10.1038/nphys1404 from abstract
The DOI link didn't work originally.
That’s a great invention - with proteins it’s not so much about in what order the elements are attached to one big molecule , but it’s the folding and coiling - how the molecules are arranging themselfs - often in very complicated chrystal structures.
If it’s about chrystal structures there’s only one good way to find out how it looks - and that’s brillant x-rays that normaly come from an accelerator with a small nuclear reactor attached.
In a year or two you can have that type of analytics in a properly equipped chemical or biological institute at the university in the next large town.
Not to mention that x-ray laser are badass weapons of the future.
Needless to say, this is a horrible explanation. The Lyman series is in the far UV, and is the result of electrons falling into the ground state of H from higher orbits. The Lyman-alpha line, caused by electrons dropping from the first excited state to the ground state, has a wavelength of about 121.5 nanometers, and the series terminates at about 91 nanometers, which represents electrons falling into the ground state from the "continuum", that is low energy passer-by electrons.
So how do they get a wavelength of 1/5 the Lyman limit? As far as I can surmise, the magenetic fields are used to place the Hydrogen nuclei ( protons ) in an environment of high energy electrons circulating in a magnetic field, so that the Lyman limit is displaced to a higher energy.
That's as far as I can make sense of it, but I hope it's close!
Give them a couple of billion and I bet they can build it as big as a three football fields at 1/10 the efficiency.
Wait til the government starts developing technology. Then you’ll really see macroscale tech!
Dunno, Doc. I could grasp “wiggling electrons” better than your explanation.
Does it fit on a shark?
Not quite right. Some of the near light speed electrons are picked up and accelerated much more by the electric field of the E-M laser light. Those electrons are focused and sent through a “wiggler” or “undulator” that forces them to give up that energy gained. The peak of that radiation is a function of the wiggler design, which is chosen in this case to be both reasonably efficient, and of practical experimental value.
LOL... well, I give you solid partial credit. I’m a soft grader- don’t tell the students I had for relativity and quantum mechanics that, though! Undulators and wigglers are rather similar, but wigglers have a more “white” spectrum whereas undulators have a very “spiked” spectrum. I don’t blame you for missing that single line “electrons ride like a surfer” in the article. That concept is very common in current accelerators, but it is now being implemented via the E-Field in Laser light. It is unlikely to ever be a concept that will allow the most rigorous experiments to be done, but it will allow good “proof of concept” experiments to be tested that can then be ported to one of the high ability “international-class” accelerators for data taking.
One of the interesting things to me about this is that one of my friends was one of the pioneers of the femto-second lasers when he was a post-doc about 15-20 years ago, and he showed me prototypes of these devices... though his was about a factor of ten shorter pulse in design, these current devices are pretty reliable now. Pretty impressive advances, to me.
Laser pulses fired into hydrogen produces intense x-rays.Thanks neverdem. Wonder if this could be adapted for SDI? Ed Teller came up with a (probably unworkable) idea for X-ray lasers generated from orbit by nuclear implosion.
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