MSimon wrote:Current flow depends on potential and load. It has zero to do with charge canceling.
Any device capable, even in principle, of running in steady state has to obey null summation of currents. No part of it can supply a current without a replacement current coming in from somewhere else.
The decelerator grid is one end of an open circuit. (I hope you haven't forgotten that at 0 Hz a capacitor looks like an open circuit.) The only way a current could flow in it, steady-state, is for it to flow around the grid between two contacts, which has nothing to do with the decelerator grid's function and won't generate any power.
So what's the other end of this open circuit? A voltage supply. Probably closely connected with the magrid power handling system, since they're at roughly the same large-scale floating voltage (as opposed to the collector).
The MaGrids are practically useless as electrostatic collectors. At even 200 KV (high energy density lower Q machines) they will collect about 15% of the available energy. Provided the collector plates are right at the surface of the magnetic bottle. A big no no as that ruins electron oscillation.
That's not what I meant.
Consider the assembly of magrid, decelerator grid, and collector. What is the potential difference between the collector and the decelerator? 2 MV. What is the potential difference between the magrid and the decelerator? 200 kV or less.
Now remove the decelerator, keeping everything else the same. What is the potential difference between the collector and the magrid?
Naturally you can't actually run a BFR this way. But it illustrates my point.
The essence of the power cycle is that the alphas in the core (ie: at the magrid) are at the bottom of a massive potential well. Alphas that are fired out from the core (this is free energy for the purposes of the electrostatic analysis) represent a current across a voltage - between the magrid (which is sucking up electrons at the same rate in amps (net, counting the e-guns) as the alphas are streaming outwards) and the wall (which is giving up electrons to the alphas at the same rate in amps as they are arriving at the wall).
Sounds like a closed circuit to me. Furthermore, it behaves as expected if you short it (the potential difference collapses and you have a thermal system) or isolate the hot terminal (massive voltage buildup, at least for the first nanosecond before the alphas stop being able to reach the wall at all).
The sole purpose of the 'decelerator' grid is to flatten the bottom of this megavolt-range potential well so that a recirculating wiffleball machine can happily operate in it.