Giorgio wrote:Holes in the x-Ray thermal collection system, not holes that will allow x-Ray to escape out of the system.
They're the same thing. This is what you don't seem to be grasping - the whole radiation shield needs cooling anyway. According to my BoE calculations, with a foot of lead to knock out the p-¹¹B gammas, even a 100 MW reactor (assuming 5% bremsstrahlung) is probably powerful enough to melt the inner layer of the shield via x-ray heating alone...
The problem is if the heat collected in those can be totally feed in a practical way to the main active cooling loop that will feed the steam section of the plant. Unfortunately most of the time this is not possible. Subsystems cooling loops will have to deliver the collected heat somewhere into the main cooling loop via heat exchangers.
I don't see this as a big problem. There aren't all that many cooling loops that need to deal with substantial power levels, and linking them together shouldn't be a big deal.
Think of this as a black box. We have connections in and out, representing a few percent of the total surface area, and these are the
only ways for heat to leave without passing through the shield cooling system. Running the shield coolant past these connections first, before flowing it through the shield, could mitigate these losses if it is considered to be worth worrying about.
The only significant potential loss mechanisms I can see are the direct-converter cooling system and the outer jacket cooling loop for the magnets - these will have to be linked together with the shield cooling system somehow, either via heat exchangers or by virtue of being different lobes of the same system. (The actual cryocooler(s) will be dealing with a much smaller power load and can be neglected; I was mashing terms together last night due to being really tired).
[As an aside, it occurs to me that the magnets will need a bit of radiation shielding as well; we can't have x-rays depositing substantial amounts of power in the superconductors, now can we?]
It's certainly no worse than a coal-fired power plant.
That's quite an assumption.
Okay, I probably shouldn't have said it that strongly without any numbers to back it up. But I still can't see the losses being a substantial fraction of the total bremsstrahlung power.
We do not even know yet the amount nor the distribution nor the energy distribution of the x-Ray that need to be removed.
We don't need to. It all comes out as heat near the inner wall of the shield, regardless of energy distribution. All we need to do is tailor the coolant flow rate to get a reasonable hot-side temperature for a power plant.
After you blithely handwaved away the difficulties inherent in turning Polywell into a launch vehicle technology, I have trouble understanding why you're suddenly so pessimistic about this... after all, the ARC-QED engine's operation depends on being able to collect virtually all the waste heat with a single hydrogen cooling loop at a peak temperature in the range of
1800 K...