Mass comparison of Focus Fusion and Polywell systems

93143 · Post by **93143** » Tue Oct 12, 2010 9:33 pm

I believe the maximum field and current increase significantly if you use liquid helium instead of liquid nitrogen. Also, MgB is probably better at withstanding neutron bombardment, if it's made with pure ¹¹B...

Note that on your linked document, the magnetic field record in the sidebar was made at 4.2 K...

GIThruster · Post by **GIThruster** » Tue Oct 12, 2010 9:41 pm

from another thread:

Ivy Matt wrote:Sorry, that's what I get for relying on memory. A working 5MW reactor is supposed to be cycled at 330Hz. The Hz/kHz confusion was just sheer laziness on my part, but I could have sworn I read somewhere that it was supposed to be 500Hz. *shrug* The patent mentions a pulse rate of 1kHz, and somewhere on the Focus Fusion forums there's a mention of a pulse rate of as much as 1.5kHz.

Oddly enough, according to the patent, the capacitors have a cycle time of 500kHz, but I don't think that's where I got the 500 number from.

That's great news. Means you can run a bank of 1,500 thrusters off a single bank of caps.

GIThruster · Post by **GIThruster** » Tue Oct 12, 2010 9:46 pm

93143 wrote:I believe the maximum field and current increase significantly if you use liquid helium instead of liquid nitrogen. Also, MgB is probably better at withstanding neutron bombardment, if it's made with pure ¹¹B...

Note that on your linked document, the magnetic field record in the sidebar was made at 4.2 K...

All true but in this application, the reduced cross section of the loops is probably the driving factor. Certainly in any mobile application (like a thruster) you would likewise avoid liquid helium.

TallDave · Post by **TallDave** » Wed Oct 13, 2010 2:37 am

I think the Poly is going to scale better than some suspect, based entirely on this YBCO tape, presuming it is not fragile towards things like X-Rays

Have we calculated the xray load for 100MW?

93143 · Post by **93143** » Wed Oct 13, 2010 3:49 am

GIThruster wrote:Certainly in any mobile application (like a thruster) you would likewise avoid liquid helium.

I wouldn't say "certainly".

The thermal jacketing is thinner, yes. But you have to make the magnet a lot bigger to get the same current, and also to reduce the peak field at the magnet edge below the critical value while still keeping the field high at the wiffleball edge.

GIThruster · Post by **GIThruster** » Wed Oct 13, 2010 4:06 am

Well, maybe just my predisposition to avoid He like the plague. Keeping something that cold so close to something so hot has got to create serious issues. Even running at 77*k is going to be difficult, don't you think? there is enough difference in what's necessary for 4k and 77k, that the new HTSC's like YBCO are revolutionizing several industries. There's miles of YBCO tape being laid from New York to Japan. All manner of generators and motors being built. None of this stuff was done with the old LTSC needing He. Stuff that cold is a real problem on lots of levels.