5 ms·

Bad ass! Our E&M professor was kind of flabbergasted that we weren't doing table top colliders (this was a decade ago), almost implying some sort of scam was go

Bad ass! Our E&M professor was kind of flabbergasted that we weren't doing table top colliders (this was a decade ago), almost implying some sort of scam was going on. Do most people know that alchemy has been realized in modern physics? Lead has indeed been converted to gold (at terrible efficiency)!

akomtu 4y ago
The alchemy moment will be when a laser impulse (made of a cardboard, a stick and a couple mirrors) assumes the shape of the gold nucleus.
TedDoesntTalk 4y ago
> Lead has indeed been converted to gold Seaborg did it in 1980 but with bismuth. “It would cost more than one quadrillion dollars per ounce to produce gold this way.” And that’s in 1980 dollars :) https://youtu.be/dpBwlcUZZRI https://youtu.be/dpBwlcUZZRI
- system2 4y ago
  At least we know we can come up with more gold if we deplete the planet one day.
  - irrational 4y ago
    But only Uncle Scrooge will be able to afford it.
    - sulam 4y ago
      Money is an artificial construct. If it’s worth doing, it will be affordable to those who get value out of it.
      - jchw 4y ago
        Money is made up, but cost is real. It's not the dollar value that matters here.
        v4dok 4y ago
        Ultimately it's energy. And as long as the output is valued enough, we would put the energy there. It would be a terribly inefficient/poor world but it could be done. Unless we have so much energy available that the cost is negligible.
        jchw 4y ago
        Energy is finite, and without some form of subsidy this kind of use case has to compete directly with everything else that we use energy for. Production of usable energy is not free...
      - andrewflnr 4y ago
        This is a very optimistic take on the efficient market hypothesis, and not one that's well supported by the evidence IMO.
      - antonvs 4y ago
        This is like saying that miles are an artificial construct. The problem is that distance is not. Or in pop-Zen terms, don’t mistake the finger for the moon.
noobermin 4y ago
If you want the lowdown from an expert, the issue with these acceleration schemes with lasers is the accelerated beams aren't that great in terms of characteristics, specifically they tend to not have the best divergence and energy spread compared to traditional linacs (divergence is better for electron beams from LWFA but for the ion accelerators which are another major application of intense laser interaction with plasma, the beam characteristics are much worse). With a cyclotron or a linac you control everything a lot better because the involved fields are fields you put in yourself with equipment you can tinker with, but here the plasma bubble is microscopic and the relevant physics happens on a femtosecond-to-picosecond time scale, and any small issues with the input laser (specifically the wings of the gaussian pulse) mess things up. One of the issues that I sort of sniffed out in the field is as a whole they are pushing for higher and higher peak energy without really looking to improve beam quality, that is, everything below the peak. Like this paper (which an old colleague is an author on!! Congrats to him) is actually pretty good on the divergence as 1mrad (mili radians) but the energy spread is 15% around the peak, which is good for some things, but there are experiments with linacs that require percent spreads less than a percent. Now, you can probably "filter" out the energies you don't want out of the beam to make it even more monoenergetic, but for example this beam has tens of picocoloumbs. Assuming (very generously, haven't read beyond the abstract yet) that most of the tens of pico they report is in that 15% spread, 1% means you might be dipping into less than a picocoloumb territory on target for your experiment, which might not give enough dose for what you need to probe or otherwise do. Anyway, in terms of the field, this work is fantastic, and generally Howard and Jorge are fantastic scientists (never met Jorge but Howard's a real decent man), but this is the cream of the crop of what we as a field can currently do. I feel like getting to the point where we give the traditional accelerator types a run on their money is still a few years out.
- fnands 4y ago
  Thanks for the input. I've been hearing about wakefield accelerators for a long time, but never got into the nitty gritty of it. Is the beam quality a fundamental limiting factor, or is it solvable (at least theoretically). It sees they're going for the get the energy up and solve the beam characteristics later approach

akomtu 4y ago

The alchemy moment will be when a laser impulse (made of a cardboard, a stick and a couple mirrors) assumes the shape of the gold nucleus.

TedDoesntTalk 4y ago

> Lead has indeed been converted to gold Seaborg did it in 1980 but with bismuth. “It would cost more than one quadrillion dollars per ounce to produce gold this way.” And that’s in 1980 dollars :) https://youtu.be/dpBwlcUZZRI https://youtu.be/dpBwlcUZZRI

system2 4y ago
At least we know we can come up with more gold if we deplete the planet one day.
- irrational 4y ago
  But only Uncle Scrooge will be able to afford it.
  - sulam 4y ago
    Money is an artificial construct. If it’s worth doing, it will be affordable to those who get value out of it.
    - jchw 4y ago
      Money is made up, but cost is real. It's not the dollar value that matters here.
      - v4dok 4y ago
        Ultimately it's energy. And as long as the output is valued enough, we would put the energy there. It would be a terribly inefficient/poor world but it could be done. Unless we have so much energy available that the cost is negligible.
        jchw 4y ago
        Energy is finite, and without some form of subsidy this kind of use case has to compete directly with everything else that we use energy for. Production of usable energy is not free...
    - andrewflnr 4y ago
      This is a very optimistic take on the efficient market hypothesis, and not one that's well supported by the evidence IMO.
    - antonvs 4y ago
      This is like saying that miles are an artificial construct. The problem is that distance is not. Or in pop-Zen terms, don’t mistake the finger for the moon.

noobermin 4y ago

If you want the lowdown from an expert, the issue with these acceleration schemes with lasers is the accelerated beams aren't that great in terms of characteristics, specifically they tend to not have the best divergence and energy spread compared to traditional linacs (divergence is better for electron beams from LWFA but for the ion accelerators which are another major application of intense laser interaction with plasma, the beam characteristics are much worse). With a cyclotron or a linac you control everything a lot better because the involved fields are fields you put in yourself with equipment you can tinker with, but here the plasma bubble is microscopic and the relevant physics happens on a femtosecond-to-picosecond time scale, and any small issues with the input laser (specifically the wings of the gaussian pulse) mess things up. One of the issues that I sort of sniffed out in the field is as a whole they are pushing for higher and higher peak energy without really looking to improve beam quality, that is, everything below the peak. Like this paper (which an old colleague is an author on!! Congrats to him) is actually pretty good on the divergence as 1mrad (mili radians) but the energy spread is 15% around the peak, which is good for some things, but there are experiments with linacs that require percent spreads less than a percent. Now, you can probably "filter" out the energies you don't want out of the beam to make it even more monoenergetic, but for example this beam has tens of picocoloumbs. Assuming (very generously, haven't read beyond the abstract yet) that most of the tens of pico they report is in that 15% spread, 1% means you might be dipping into less than a picocoloumb territory on target for your experiment, which might not give enough dose for what you need to probe or otherwise do. Anyway, in terms of the field, this work is fantastic, and generally Howard and Jorge are fantastic scientists (never met Jorge but Howard's a real decent man), but this is the cream of the crop of what we as a field can currently do. I feel like getting to the point where we give the traditional accelerator types a run on their money is still a few years out.

fnands 4y ago
Thanks for the input. I've been hearing about wakefield accelerators for a long time, but never got into the nitty gritty of it. Is the beam quality a fundamental limiting factor, or is it solvable (at least theoretically). It sees they're going for the get the energy up and solve the beam characteristics later approach