Maui wrote:I apologize if this has been discussed elsewhere, but can someone explain what they mean when they say they plan to recapture the helium and reuse it (solving supply problems). Do they mean just the un-reacted He-3?
With little specifics on their plans, I will still speculate on possible paths they may be considering. The D-He3 fusion cross section peak is at a higher temperature than likely D-D or D-T cross section target temperatures. The base D-D reactions may be sufficient at a temperature of ~ 60 KeV. This is a little above the D-T fusion cross section peak, but still well below the D-He3 target which may be ~ 100-120 KeV.
Assuming the FRC plasma is thermalized, the fusion ions will thermalize with the deuterium, perhaps even reaching ignition conditions (self heating).
Under these example conditions., the initial pure deuterium fuel will fuse at hopefully adequate levels and produce tritium and He3. The D-D reactions may not be reaching breakeven, but the tritium produced will rapidly react with additional deuterium to produce ~ 4 times as much energy per reaction and perhaps have near complete burn up of the tritium. In this situation, I think the D-T secondary reactions would produce most of the fusion energy, driving the system to profitability. Some small percentage of the He3 may react, but most may not. It would persist in the plasma until the end of the pulse. The plasma is then exhausted and the He3 is collected and purified. It is a valuable end product of the reactor. Any non reacted tritium would also need to be sequestered, perhaps more for safety reasons rather than as a commodity.
The advantage of utilizing produced tritium in this way is that it contributes considerably to the fusion power output, and it is essentially free. There is no complex tritium breading needed, you just use the side product tritium as is, there is no need to generate more tritium than you consume as there is with pure D-T fusion machines. This is similar to the so called 1/2 catalyzed D-D reaction that has been promoted for boosting Polywell yields. The difference is that in a Polywell, the produced tritium and He3 do not thermalize with the fuel deuterium, they naturally leave the system quickly and would need to be collected, and reinjected into the system at desired temperatures. A thermalized machine may not need this extra step. This may even be an attractive situation for Tokamaks as well, provided the temperatures can be pushed high enough for D-D reactions to proceed at an adequate rate (my impression is that this is highly unlikely).
As the He3 is a mostly unused product of the reactor it is available for collection for any appropriate use. Optimistically, several D-D reactors used for grid electricity production would produce enough He3 to power a dedicated D-He3 aneutronic reactor aboard an ocean ship or space ship. As such, the mining of He3 on the Moon is not needed, Adequate He3 would be available at very much cheaper prices.
To error is human... and I'm very human.