Can anyone tell me if enough R&D has been done on deceleration grids (for the direct-conversion electric generation approach), to determine what sorts of physical limits there might be (at least, with the current generation of the technology)?
What I mean is, I don't know this for sure, but I imagine that even with an efficient grid, some amount of the power from the fusion reactor will be 'wasted' as heat in the grid material itself. If that's true, then it seems like, probably, as you ramp up the power of the reactor, you might hit a point where the waste heat becomes a problem?
I can think of a couple ways it might be a problem - in many materials, isn't it true that as they heat up, their resistance increases? Of course, heat anything up enough and it will start to become permanently damaged.
So, based on that, can we say that, at least in the near term, there is some theoretical maximum output power for a p-11B reactor (e.g. 100MW, 1GW, 10GW, whatever), where if you try to make it more powerful than that, even though you might get increased fusion, you can't 'capture' that power efficiently any longer?
What is the basic principle at work in a deceleration grid? Is it that, after the fusion reaction, the charged particle (does the reaction emit protons, or electrons?) 'explodes' out of the reactor core at a very very high speed (so it has a high amount of kinetic energy), and the deceleration grid exerts an opposed force on the charged particles as they approach the grid, which opposed force a) slows down the charged particle from the reactor, and b) begins to accellerate electrons in the grid, producing current flow?
Or is it some other principle - maybe if electrons are being emitted directly from the core, they are 'grabbed' up by the grid and diverted into whatever conductor is used to move current out of the reactor to whatever use it's being put to?
Deceleration Grid limits?
The grid is tuned to the 2.46 MeV alpha particle; The 3.26 MeV particles give the rest of their energy in a wall collision. So, 0.8 MeV as heat, 7.38 MeV as electricity.
There is another 0.1% that will be low cross section reactions, but that pales in comparison to the ~10% higher energy alpha losses. Also there will be some amount of high energy alphas colliding with the grid, despite the magnets.
There is another 0.1% that will be low cross section reactions, but that pales in comparison to the ~10% higher energy alpha losses. Also there will be some amount of high energy alphas colliding with the grid, despite the magnets.
Wandering Kernel of Happiness
It is not that simple. The energy of the alpha particles (with P-B11 fusion) is the sum of their birth energy and the existing velocity of the parent particles at the instant of fusion and/ or subsequent decay products. I envision the direct conversion grid made up of multiple grids or blinds at cascading voltages to harvest the kinetic energy of the charged particles as they pass. The particles inertia and/or magnetic fields prevent the particles from curving into the grids till most of their energy is bled off- along the lines of a mass spectrometer. Ideally, with enough small voltage gradients between many blinds (venation blind arrangement) the conversion efficiency might approach 100%. But, practical considerations and compromises leads to the presumably much easier obtained efficiencies of ~ 80%
Dan Tibbets
Dan Tibbets
To error is human... and I'm very human.