I was thinking of it in terms of a flux of ions carrying 100 MW of power out of the reaction. My thinking was, even a small fraction of 100 MW hitting a neutral grid is going to cook the grid. So, are you saying that the intercept rate of ions to the neutral grid is going to be vanishingly small? Or that the ions aren't carrying that much power? Or ???
Sure, I understand that once the He ions get past the neutral grid the bias in the decelerator grid will slow them down, do work on that E field, and deliver only a tiny remaining KE to the final grid. But they have to clear the neutral grid first.
Net energy question
The "equalization grid" IS the trap grid. The outer shell should be at +1.7 MV, and the trap grid should be at ground, so it assumes the burden of all the negative charge required to go from almost 2 MV to 0. By Gauss' Law the high-voltage shenanigans out there will be invisible to anything inside the radius of the trap grid, and if that grid is technically grounded, we don't have to float the reactor at high voltage to take advantage of this effect.
BTW, as I recall the plan was in fact to have the alphas obtain electrons from the outer wall. This would of course be good for charge conservation, but another important idea is that the ion be removed from the electrical environment so that it doesn't get fired back out into the reactor at the same energy it had when it passed the first trap grid (there should probably be multiple grids, since not all alphas have the same energy; charge exchange is a problem for the scheme as stated, but hopefully not an insoluble one). I think it's also possible that there could be a bit of an electron plasma near the wall, caused by leakage off the decelerator grids; this could increase the cross section for helium formation from slow alphas near the wall...?
EDIT: It just occurred to me (after reading a post from Tom Ligon at nasaspaceflight that says exactly the following) that it might be wiser to have the high-voltage stuff happening inside the chamber, rather than outside. In this case the result would be a large negative potential on everything inside the vacuum chamber, and an outer wall at ground. That's a design decision, I guess, but there's got to be some grounded shielding between the MV-range stuff and the personnel area regardless...
BTW, as I recall the plan was in fact to have the alphas obtain electrons from the outer wall. This would of course be good for charge conservation, but another important idea is that the ion be removed from the electrical environment so that it doesn't get fired back out into the reactor at the same energy it had when it passed the first trap grid (there should probably be multiple grids, since not all alphas have the same energy; charge exchange is a problem for the scheme as stated, but hopefully not an insoluble one). I think it's also possible that there could be a bit of an electron plasma near the wall, caused by leakage off the decelerator grids; this could increase the cross section for helium formation from slow alphas near the wall...?
EDIT: It just occurred to me (after reading a post from Tom Ligon at nasaspaceflight that says exactly the following) that it might be wiser to have the high-voltage stuff happening inside the chamber, rather than outside. In this case the result would be a large negative potential on everything inside the vacuum chamber, and an outer wall at ground. That's a design decision, I guess, but there's got to be some grounded shielding between the MV-range stuff and the personnel area regardless...
Last edited by 93143 on Thu Oct 25, 2007 9:35 pm, edited 1 time in total.
Yes. The farther away grids will have way more area vs heat load than the mag grid.Stefan wrote:My point was that the power lost to the neutral grid would be a relative small fraction of the total power.
Anyway the problem is to keep the MA-grid cooled, compared to that grids further away are easy.
The purpose of the father grids is not to collect particles. Their purpose is to collect charge from moving alphas. The outer vacuum wall of the reactor may need to be at MEV with a further electrical shield wall around that. The alphas need to be neutralized at the end of their travels.
Electrical isolation is going to be a really fun problem.
Of course when it is all done and working the design will be obvious. Heh.