The "Knobs" discussion (aka "Art and Rick, love at first site"
)
from Cosmic Log:
http://cosmiclog.msnbc.msn.com/archive/ ... 36887.aspx
Rnebel responded;
"1. The theory says that you can beat Bremstrahlung, but it's a challenge. The key is to keep the Boron concentration low compared the proton concentration so Z isn’t too bad. You pay for it in power density, but there is an optimum which works. You also gain because the electron energies are low in the high density regions.
2. The size arguments apply for machines where confinement is limited by cross-field diffusion like Tokamaks. They don't apply for electrostatic machines.
3. The Polywell doesn't have any lines of zero field. Take a look at the original papers on the configuration. See :
Bussard R.W., FusionTechnology, Vol. 19, 273, (1991) .
or
Krall N.A., Fusion Technology. Vol. 22, 42 (1992).
Furthermore, one expects adiabatic behavior along the field lines external to the device. Thus, what goes out comes back in. Phase space scattering is small because the density is small external to the device.
4. The machine does not use a bi-modal velocity distribution. We have looked at two-stream in detail, and it is not an issue for this machine. The most definitive treatise on the ions is : L. Chacon, G. H. Miley, D. C. Barnes, D. A. Knoll, Phys. Plasmas 7, 4547 (2000) which concluded partially relaxed ion distributions work just fine. Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement.
5. The system doesn’t have grids. It has magnetically insulated coil cases to provide the electrostatic acceleration. That’s what keeps the losses tolerable.
6. The electrostatic potential well is an issue. Maintaining it depends on the detailed particle balance. The “knobs” that affect it are the electron confinement time, the ion confinement time, and the electron injection current. There are methods of controlling all of these knobs."