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from the is-that-a-particle-accelerator-in-your-pocket? dept.
Phys.org has the story on new research demonstrating an extremely small particle accelerator that uses lasers to generate terahertz frequency pulses of light to accelerate electrons.
Scientists have successfully developed a pocket-sized particle accelerator capable of projecting ultra-short electron beams with laser light at more than 99.99% of the speed of light.
To achieve this result, the researchers have had to slow down light to match the speed of the electrons using a specially designed metallic structure lined with quartz layers thinner than a human hair.
This huge leap forward simultaneously offers the ability to both measure and manipulate particle bunches on time scales of less than 10 femtoseconds (0.000 000 000 000 01 seconds, or the time is takes light to travel 1/100th of a millimeter). This will enable them to create strobe photographs of atomic motion.
Particle accelerators are widespread with applications in basic research in particle physics, materials characterisation, radiotherapy in hospitals, where they are used to treat cancer patients, radioisotope production for medical imaging, and security screening of cargo. The basic technology (radio-frequency oscillators) underpinning these machines however, was developed for radar during the Second World War.
In new research published today in Nature Photonics, a collaborative team of academics show that their unique solution is to use lasers to generate terahertz frequency pulses of light. Terahertz is a region of the electromagnetic spectrum between infrared (used in TV remotes) and microwave (used in microwave ovens). Laser-generated THz radiation exists in the ideal millimeter-scale wavelength regime, making structure fabrication simpler but most importantly providing the half-cycle lengths that are well suited for acceleration of whole electron bunches with high levels of charge.
In addition to applications such as radiotherapy and imaging, in the long run the researchers feel this technology could potentially be used to replace miles-long particle accelerators in use today with devices only meters in length.
Journal Reference
Hibberd, M.T., Healy, A.L., Lake, D.S. et al. Acceleration of relativistic beams using laser-generated terahertz pulses. Nat. Photonics (2020). DOI: 10.1038/s41566-020-0674-1
(Score: 3, Interesting) by stormwyrm on Wednesday August 12 2020, @04:49PM (5 children)
So if it's at 0.9999c, the electron energy would be ½(9⋅10-31 kg)⋅(0.9999c)2 = 250 keV. This would have required a voltage of at least 250 kV (probably substantially more) to produce such high-energy electrons. Highly compact high-energy particle accelerators are the obvious application, but might it then be possible to make a desktop-sized electron microscope with this technique? Or something like an orthovoltage x-ray machine? These are somewhat large and unwieldy pieces of equipment right now to say the least.
Numquam ponenda est pluralitas sine necessitate.
(Score: 0) by Anonymous Coward on Wednesday August 12 2020, @11:00PM
Now we just have to reliably generate 250kV in a pocket-sized form factor...
I once hacked together a 6kV connector for an ion pump from a 2mm ferule crimp, an inch of steel tube and some heatshrink. I'll be giving DIY 250kV connectors a miss.
(Score: 2) by ChrisMaple on Wednesday August 12 2020, @11:59PM
There already are desktop size electron microscopes.
(Score: 2) by FatPhil on Thursday August 13 2020, @12:00PM (2 children)
"To achieve this result, the researchers have had to slow down light to match the speed of the electrons using a specially designed metallic structure lined with quartz layers thinner than a human hair."
So it's 0.9999 * alpha * c, where alpha is some suitably small fraction that the summary does not disclose.
Personally, I don't like the description "speed of light" to be anything apart from c. "Speed of light in vacuo" is just arse covering, and shouldn't be needed. The speed of propagation of the electromagnetic force in *any* medium (which is almost entirely vacuum, no matter what the medium is) is c. However, in some media, the induced magnetic field in the material generates a wave in the electric field, which when combined with the original wave such that the combined fields appear to have wavefronts that advance at a speed lower than c. So these materials have an *apparent* or *effective* speed of light that is less than the "speed of light". However, I only got cranky about it after I saw the explanation using Maxwell's equations themselves (which only use c), and I can understand why people who have the wrong idea about why light "bends" or "slows down" through water/glass/whatever would have a different view on what language is appropriate. So I guess it's best to just keep covering your arse and explicitely use "in vacuo" or "in [the material/medium]". Which they didn't do. Grrr.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by hubie on Friday August 14 2020, @05:38PM (1 child)
I think you're being a bit too pedantic with your objection to "speed of light in vacuo." For sure c falls out of Maxwell's equations when you assume free-space propagation, but in a practical sense, even in the physics community, you typically are talking about interactions in a medium, so you care about propagation speeds in materials. When speeds of effects start getting comparable to c, then you talk about how they compare to the ultimate (in vacuo) speed. In equations, c is always taken to be the in vacuo value, so you never need to distinguish it there. Transmission line engineers or optical or solid state physicists always want to know the speed of light through the system and they don't care too much about the micro or nanophysics of what is going on, unless that is important to their research. For an effect like Cherenkov radiation (radiation emitted when a charged particle is moving faster than light through a medium, thus creating an "optical shock wave"), you absolutely need to discuss the two different flavors of c if you want to understand the effect.
(Score: 2) by FatPhil on Friday August 14 2020, @10:06PM
If you are manipulating the medium deliberately such that you manipulate the speed of light in that medium, and then you don't make that clearly obvious in your anouncement, then you are being a knobend.
They were being knobends. I am calling them out on that. Feel free to disagree.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves