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Comment by AllegedAlec | Hacker News Reader

> Sapra et al. developed an integrated particle accelerator using photonic inverse design methods to optimize the interaction between the light and the electrons. They show that an additional kick of around 0.9 kilo–electron volts (keV) can be given to a bunch of 80-keV electrons along just 30 micrometers of a specially designed channel.

A lot less exiting than techcrunch says, but I wouldn't know why I expected better.

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The exciting part of this is the gradient. The addition of 1keV in 30um is huge!

For reference, in a typical electron microscope, accelerating fields might reach a 1 MeV/m gradient. In these cases, it's usually an anode (-200kV) and cathode (0V) closely separated. High vacuum is required, it's large, power supplies are enormous, etc.

Scaling the results of this paper, especially after a working prototype, will be more interesting to the general population. But the key discoveries are already here. Scaling becomes an engineering concern.

So what’s stopping us from being able to convert energy to mass with a particle accelerator? Shouldn’t it be possible to get a particle of equivalent mass-energy to the energy concentrated by an accelerator? So like amp up an electron to 106 MeV and get a muon-on-demand?

Well, muons are made by getting electrons or other particles up to high speeds and then crashing them into stationary targets or counterrotating beams. But you have to create muon-antimuon pairs, so that requires at least 212 MeV in theory and much more in practice because of energy lost to heat, etc. https://www.fnal.gov/pub/today/SpecialROW032808MERIT.html

Per google, you have to have a collision because of the law of conservation of momentum otherwise won’t allow for pair production. It’s an open question how we get a universe of matter out of seemingly only producing mass energy in matter/anti-matter symmetry. Sounds like a sure Nobel prize for that one, too.

Is there any reason they couldn't chain a whole bunch together to kick up to higher energy levels? Say you need 50um per segment for the support framework and whatnot, you could pack 200 of them in a cm long instrument and kick up the power by 200keV?

Oh yes, that's what I would anticipate.

The design shown in this paper is specific to an initial electron energy of 83keV. That means that chaining identical parts wouldn't work, but you could have an array of similar parts with slightly different properties at each "stage".

900V/30μm is likely to be very useful indeed. At that gradient, the threshold for positron-electron pair production is about 34mm, which is small enough I can — for example — imagine it being built into a surgical instrument specifically intended to be pushed into a tumour.

As I am not a biologist, I have no idea if that is actually a useful way to deal with tumours, but regardless of the specifics I definitely expect it to enable things that are not currently practical.

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