Bro this did not deserve a badge, but thank you! In theory, you should be able to heat whatever-mak plasma with photons, certainly. (for posterity) Inertial confinement fusion uses lasers to fuse. I would guess that the reason the magnetic confinement folks don't really rely on lasers for heating is that whatever particles are bouncing around the vacuum chamber will go into the beam source and fairly quickly ruin whatever material you're using to lase? Honestly, I'm not sure why an energetic neutral beam source would be superior, except for something to do with component degradation being more easily/cheaply dealt with. People are working on the laser'ing method. And of course, if you're using UV or anything shorter wavelength, if you put the laser outside the chamber, behind a glass flange thick enough to hold up under the pressure differential, you're gonna lose a lotttttt of photons inside the glass. Very related, and not mentioned in the blog: Plasma-chamber material considerations are serious business. So even if you've got an infinitely stable confinement, you will still eventually have to cease your fusing mode for a mode of operation that reliably restores the intended coating(s) inside the chamber and sweeps away the large "dust" molecules. It's disheartening that it's 2022 and we're still at "Well we can't really simulate this until we have quantum computing clusters, probably, but we'll do the best we can, and if it seems like a new configuration or approach could work, maybe we'll get the money to build it. Maybe it will even kinda work!". But such is plasma confinement. One of my profs, very candidly one day went into a rant that started with: "Look... Look. Plasma... is.. not your friend." I have been wondering if there's a very different approach from all of this that might be superior. Instead of using the energy from fusion to boil water and going through turbines to generate electricity, if you're clever enough, you might be able to go straight to generating a voltage across the chamber (edit: Yes, I know, a chamber with a potential across it sounds like a nightmare, if not impossible, not sure how you'd have anything, like instruments, sources, the beloved tinfoil sheet barely obscuring some glass, etc., hooked up to it :(. That problem aside, you could have some periphery electronics to siphon off (or in) charge however you need, the same sort of idea as a Marx generator, but maybe in reverse?). Then, instead of aiming for loooooong confinements, engineer the thing to lose confinement (albeit in a controlled manner) every 1/60th of a second. Of course, that's still a long time, as far as the plasma's concerned (typical ion gyrofrequencies for magnetic confinement fusion plasmas are ≳ 1E7 Hz, with electrons ≳ 1E10 Hz). Still shaves off a couple or several orders of magnitude from your targeted confinement time. I kinda doubt either of these directions would work out, ultimately. 'nother edit: Yeah, it'd be.. even harder, I think, to make anything close to a sine wave shape, you'd need something inherently lossy to shape fusion-outputted waveforms back to sine-like. Unless. you had a large array of units that you could use systematically... 'nother 'nother edit: Also I think it is loss of confinement that is to blame for the most egregious dusting/doping events, so maybe planned, routine loss of confinement is just plain stupid. In general, I'm loathe to search the literature outside of my current regime. I'd much rather show up at a conference, find some experts, and ask my foolish questions. I don't care if I look stupid if it saves me huge amounts of time.a similar effect with with a laser
Ah, see, I again treated it too literally like a fluid, thinking the change (modulation?) in surface tension could introduce deeper change in flow. This itself is a trap that can only lead to instabilities down the line, but it didn't hurt to ask. Gonna have some followup questions, but that's a lot to even skim you threw there. Ain't that my call, though? The article presents a frankly abstruse topic approachably, and IMO that's amazing.Bro this did not deserve a badge
This article was a lucky find. I've already forgotten where/how. Glad you liked it :). And plasma is very fluid-like, usually (see: magnetohydrodynamics/MHD). But also, here, relativistic. And collisional. And radioactive (OK, that one's kind of a stretch). Btw, the simple-ish case of the Kelvin-Helmholtz single-fluid flow shear instability is popping off almost all of the time, like 15 Earth radii away, along the duskwards magnetopause flank. 100% MHD plasma. And then rx'n (ignore this for now). Sorry, I should've gone into more detail, but now you've got it. One main function served by the neutral beams is to heat the plasma via collisions (in tandem with the B-field), and the plasma then hopefully makes it past some critical pressure and collision frequency threshold to self-sustain and at least temporarily generate net positive energy. I would say heating via neutral beam is "the" main function, but again, H-mode. In that first configuration of the "four ways to start an FRC" cartoon in the article, the neutral beam is injected along the field. So that leads to disproportionately parallel heating of the plasma, which makes a localized (in space) anisotropy in ion (and electrons, to another degree) velocity space, which always wants to find a way to be thermalized, i.e. made fairly Maxwellian again, instead of having two (or more), or even nearly two distinct populations. In the collisionless regime, this happens via wave-particle interactions, but for fusion plasmas, it is almost always the collisions that serve as the interactions thermalizing the plasma. So uhhh anyway. The article talks about a totally different type of instability. There are often many competing instabilities, it's kind of like a race to see if good conditions are sustained for one instability's progression into the runaway, non-linear growth phase, and then that instability can go on to disrupt and/or initiate other processes. In the article's case, it's a disruption like a vortical, fluid-like eddy current, a not-quite-chamber-size perturbation in the magnetic field geometry. In most tokamak losses of confinement, Princeton, France, et al. seem to think a sustained topological resonance can enable another instability, the tearing (or plasmoid) mode, to progress into the non-linear phase and then trigger magnetic reconnection (rx'n), which rapidly breaks confinement stability. Rx'n is by far and away the most important non-linear plasma mixing process, and I suspect that rx'n is to blame for almost every significant loss of confinement. Rx'n seems typically required for rapid system-scale topological reconfigurations. We have found rx'n to be a crucial mechanism coupling the turbulent cascade of energy from large to small scales over time, in the form of electron-only rx'n resolving ion-scale turbulence; pockets of magnetic domains in a plasma, separated by ~10 ion gyroradii or ~10 ion inertial skin depths (somethin' like that, depends) with some significant component of each's magnetic field opposing the other can annihilate some magnetic flux along the axis of component reversal, converting the flux into electron energy (and not ion energy, since it's not ion-coupled). Electron-scale rx'n recently solved the coronal heating problem, yo! Big coronal mass ejections and strong flares are much more ion-coupled, though. Basically all of the mass of classical plasmas is ions, so yeah. I shall cut me off here last edit, swear on my eldest cat's life eh, oh well, she was sacrificed b/c I found the .pdf