ladajo wrote:At the least we can use the Xrays to heat water or something. Energy recovery would be the better move. Or even along the lines of some of the nano enabled solar cells, maybe we could get one sensitive to Xrays at the energy levels required.
Uhm... conversion via thermal recovery has a very little global efficiency. I guess the solution of choice will depend upon the total amount of X-ray produced.
If the amount will be a small percentage of total power it will probably make more sense to ignore them.
I'm not sure what Giorgio means by global efficiency. . But, most reactors will need active cooling with heat collection, which is used to generate electricity at perhaps 25-35% efficiency, depending on various issues. Collecting the x-ray energy in this manner is in a since free as you already need the system. In another since, if is inclusive with all of the other heat generation processes. In a large D-T burning Tokamak, the X-ray energy output is probably a small portion of the total energy output, and is not worth the effort to try to more efficiently collect and convert it, or to recycle it.
In a higher temperature Polywell, the effort to selectively collect the x-ray energy is probably impractical, at least for D-D fusion, unless other benefits dominate (such as reducing waste heat in a spacecraft). For P-B11 fusion it might help some if the Q is closer to 5, rather than 20.
In a FRC or DPF device, where the optimistic gains are closer to breakeven, the extra effort may be profitable or even essential. It is possible that this may end up being the biggest winner for E. Learner if his patented direct conversion scheme for X-rays work.
D Tibbets wrote:I'm not sure what Giorgio means by global efficiency. But, most reactors will need active cooling with heat collection, which is used to generate electricity at perhaps 25-35% efficiency, depending on various issues.
I mean efficiency of absorption of X-ray into heat and transformation of this heat into electricity. As you say there are various issues governing the final conversion efficiency, but a 25% final result is optimistic in my opinion.
A solar cell type approach perhaps. Though if the solar cells are less efficient than ~ 25% there is a net loss. Also, the cells have to be survivable, which means they have to be outside the vacuum vessel and neutron absorbing material. This would stop the vast majority of the low to mid energy x-rays. Even a modest thickness of plain glass will stop most of the X-rays below 10 KeV and a Tokamak average X-ray temperature would probably be in this range. With a Tokamak this would also require a very large surface area to cover all of the reactor. The outside surface area of a Polywell, FRC and especially DPF would be smaller, thus more cost effective to cover. Also, the plasma temperature in these machines will probably be considerably higher so the x-rays will be higher energy and more easily penetrate surrounding structures. Because of the higher temperatures necessary (unless they are burning D-T) the escaping x- rays will be carrying away a higher portion of the total energy escaping the plasma, so any conversion efficiency gains will be magnified over a Tokamak (D-T burning machine with it's necessary lithium layer).
I don't know if Learners claimed 80% efficient onion skin X-ray converter could be considered a type of photovoltaic cell, but if it works, it would be a good candidate for the x-ray direct conversion approach in the smaller machines, especially with P-B11 fuel where the Bremsstrulung X-ray output may be close to the fusion energy output.
Though the economics may not be favorable, I think 80% conversion of Bremssterulung radiation would allow for net positive energy from a P-B11 reactor, even using Rider's assumptions that the 'waste X-ray losses will be ~ twice that of the fusion output.
eg: Energy input = 10 MW (almost no containment losses), Fusion output = 5 MW, Bremsstrulung x-ray output (losses) makes up 10 MW. So the Q would be 0.5 and even if the fusion output could be converted at 100% efficiency it is a losing proposition. If the x-ray losses are salvaged at a 25% efficiency through a heat cycle, it is still a loss. But at 80% x-ray energy salvaging rate, 8 MW out of 10 could be recycled. Now the net gain is ~ 3 MW, or ~ 2.4 MW at 80% efficient direct conversion of the alphas. Steam conversion of the alphas would only allow ~ breakeven energy balance in this situation. I understand that a DPF may operate in this general range (it is a thermalized plasma like what Rider assumed), though claimed effects with extremely strong magnetic fields present in the DPF is supposed to suppress the Bremsstrulung radiation (I have no idea how much). Also having ~5-10 protons for each Boron is suspposed to help.
The Polywell with it's non thermal plasma and dynamic variation in the electron temperature may reach P-B11 Q's of 5-20 (quoted from M. Simon). This would not require the heroic X-ray loss scavenging, though it might be beneficial depending on the engineering, cost, and end purpose situations.
KitemanSA wrote:AFAIK, Lerner's technique IS the "solar cell" approach.
I think Lerner proposal was related to the use of photoelectric effect and not the use of photovoltaic effect (solar cell approach).
The two effects, while related, are quite different.
Giorgio wrote:efficiency of absorption of X-ray into heat
is likely to be close to 100%. Heat is not difficult to produce. If you have sufficient shielding to knock out 99.999999999999% of the x-rays, 99.999999999999% of the x-ray energy passing through the shield will end up as heat in the shielding. Then you just need to actively cool the shielding. Anything else the x-rays hit will either be actively cooled or will conduct/radiate its heat away to something that is.
Better yet, just about all of the x-ray energy is deposited very close to the inner wall of the reactor and shielding, so very little heat should actually escape the outer wall. An x-ray flux that's safe to stand next to is many orders of magnitude lower than one representing a significant fraction of the total bremsstrahlung power of a Polywell, so the bulk of the shielding will absorb very little heat.
Giorgio wrote:efficiency of absorption of X-ray into heat
is likely to be close to 100%. Heat is not difficult to produce. If you have sufficient shielding to knock out 99.999999999999% of the x-rays, 99.999999999999% of the x-ray energy passing through the shield will end up as heat in the shielding. Then you just need to actively cool the shielding. Anything else the x-rays hit will either be actively cooled or will conduct/radiate its heat away to something that is.
The problem I see is not the amount of conversion of the incident x-Ray on the conversion apparatus itself, but the % of generated x-Ray that you can actually bring to the conversion system.
There will still be holes where x-ray will go through, other components of the machine not actively cooled and so on. Is the sum of these total losses that I was referring to.
I personally do see a lot of difficulties if we actually had to implement an x-Ray absorption system inside a pB11 Polywell.
Giorgio wrote:There will still be holes where x-ray will go through
There better not be. People will die otherwise.
other components of the machine not actively cooled
Any heat from those will eventually find its way to either a shield penetration (which can be actively cooled, and will certainly be in very close proximity to the cooling system for the shield itself) or to a component that is actively cooled.
I personally do see a lot of difficulties if we actually had to implement an x-Ray absorption system inside a pB11 Polywell.
I don't. This system is pretty well corralled; the entire radiation shield needs cooling anyway, and thus the only ways for heat to leave uncaught are the cryo, power, fueling, exhaust, and instrumentation penetrations. The last four can be cooled specifically, or just entrusted to the care of the shield cooling system they're right next to. And they won't likely be straight-through penetrations in any case; they'll need to be periscoped to avoid compromising the shield. Any heat lost through cryo lines can be regained as well as thermodynamically necessary by preheating the shield coolant with the cryocooler hot side.
It's certainly no worse than a coal-fired power plant.
Giorgio wrote:There will still be holes where x-ray will go through
There better not be. People will die otherwise.
Holes in the x-Ray thermal collection system, not holes that will allow x-Ray to escape out of the system.
Any heat from those will eventually find its way to either a shield penetration (which can be actively cooled, and will certainly be in very close proximity to the cooling system for the shield itself) or to a component that is actively cooled.
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. This will generate losses.
I am thinking in engineering terms here.
It's certainly no worse than a coal-fired power plant.
That's quite an assumption. We do not even know yet the amount nor the distribution nor the energy distribution of the x-Ray that need to be removed.
This, IMHO, is going to be a lot more complicated to design than a simple boiler/power system. Thinking to be able to collect the whole x-Ray and transform them in thermal heat is not realistic in my opinion.
The whole point here is if there is a low Q, can we capture enough X-Ray to make a difference in favor of viability. It is an efficiency question.
The questions in my mind:
X-Ray energy production rate verses fuel burn created energy?
X-Ray Capture rate?
X-Ray energy recovery rate?
Recovered Energy use availability (efficiency)?
