a GE CF6-6 jet engine (boeing 747) is 2.19 m dia
pumps 590 kg/sec
air at stp is 1.2 kg/m^3
that gives 491,667 liters per second
scaling the area to 3.125 m dia would give 1e6 l/sec
This agrees with:
But here is one: a 3,000 l/s pump has an inlet 10 cm across (actually about 8 but I'm interested in ball parks). 1 m across would be 300,000 l/s. 3 m across would be 1 M l/s.
NASA has probably built pumps 10X as large for its very big vacuum chambers. Those could do in the range of 100 M l/s.
It is going to be an "interesting" engineering problem to fit 100 turbo pumps the size of 747 engines around a vacuum chamber.
Consider what you kid's 100 sided D&D die looks like.
And there are going to be megawatts expended just to overcome friction in that kind of vacuum system. (WAG)
OR
NASA Has built 30 M diameter vacuum pumps?
Really?
That is almost as wide as a football field. And it's going to spin HOW fast?
IIRC The 6" turbo pumps that I used turned 12,000 rpm.
I'd like to see that machine. It would be very impressive.
The final dynamic balancing of that shaft will be quite a trick too.
Vacuum loads will be aggravated by the out-gassing from the hot wall of the heat exchanger feeding the heat engine which will be needed to extract the bulk of the energy.
There had better be a way to finesse this one.
So:
If the alphas are channeled to strike the chamber walls in 14 spots 1/2 m diameter each and the chamber is 2.5 m radius (1 m more than the magrid). That gives a 24x improvement. ie the partial "pressure" of the particles is 24 times higher than if they were distributed over the whole vacuum chamber. So now we are down to 4 each 747-engine-sized vacuum pumps. That seems doable but still very expensive.
OR
Scaling the vacuum pump above the brings down the monster turbo pump's throat to a mere 12 meters or 6 meters each if we use 4 of them.
That's a lot better. But still way expensive.
This is going to cost on the order of the steam power generator that heretofore was the biggest cost item.
There had better be a better way to finesse this one.