WB-7 details?

[MSimon]

R^7 scaling only holds if you double the magnetic field every time you double the size.

Let us look at B^4 scaling. If we went from .15 T to 1.5 T that gives a power increase of 1E4. If you go from .3 m coil diameter to 3 m coil diameter you 1E3 power multiplication. total is 1E7 if you start at .1 w you are up to 1E6 w.

Increase reaction volume to 15 m on a side and you are up to 100E6 w.

Or increase the magnetic field to 5T would give you a 3 m 100E6 w reactor.

MgB is currently good to 20 T at 4 deg K. 5 T at higher temps (I'd have to look it up).

9 T at 20K has been reported. At 5 T the Jc should be higher allowing for fewer turns.

The real key isn't size. It is magnetic field.

[TallDave]

R^7 scaling only holds if you double the magnetic field every time you double the size.
...
The real key isn't size. It is magnetic field.

Yeah, iirc Bussard was assuming that was the case. Of course, a stronger B field probably means a bigger machine, but I see your point: what's the most cost-effective combination of r^3 and B^4?

[MSimon]

5 T at the center of a 3 m loop requires 25E6 Amp * turns.

http://hyperphysics.phy-astr.gsu.edu/hb ... urloo.html

Assume 4.2 deg K and 1E4 A/cm^2 (assuming ultimate Jc > 2E5 @ 5T and 4.2K allowing for fill factor of 10% and safety margin of 2X)

If the coil was square shaped it would be 50 cm on a side. i.e 20" American.

Now I may be low on the fill factor. A fill factor of 40% would give a coil 10" (25 cm) on a side.