In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.
Subject: Re: p-B11
Date: Nov 23, 9:40 pm
Poster: Tom Ligon
On Nov 23, 9:40 pm, Tom Ligon wrote:
Hirsch got his record neutron productions of something like a trillion or more a second by running an IEC machine at 150 keV. Most researchers dislike the x-rays thus produced, and the need to replace grids after a few seconds of operation. Finding a way to make a gridless system, and investing a little in x-ray shielding, would make exotic-fuel IEC possible.
>The p-B11 is attractive because of zero radiation and because of the potential for direct energy conversion, correct?
p-B11 is attractive because it allows something like 80-95% of the fusion energy to become high voltage DC useful electricity, with no neutrons or radioactive byproducts. There is some x-ray production. Don't underestimate the value of efficiency: in the typical fission plant (30% efficiency) he cooling towers cost more than the reactors, and for space propulsion a system relying on any thermodynamic cycle is prohibitive due to the radiators required.
>Well, D-He3 can come close to zero neutron emissions and pure He3 would have effectively zero emissions. D-T while having a great cross section is impractical because of the safety issues surrounding Tritium. D-D is very useful and any net output machine should be able to burn D-D if it can burn D-T.
D-T is MUCH easier to burn than D-D, which is somewhat easier to burn than D-He3. But all are easy with IEC, and easier than the exotic fuels like p-B11.
Yeah, you can burn D-He3, but the energy is hard to recover. You can tune it for 1/30 of the neutron production of D-T (still some D-D reactions). But the charged particle production energy is spread all over the place making it difficult to do direct conversion. And since it is not a neutron producer you can't breed your own fuel by activating lithium. You have to dig up the Moon to get it, or mine it from the Jovian atmosphere, etc. Or make neutrons elsewhere with D-T and activate lithium. It is a very scarce fuel in nature.
>Now, as for direct energy conversion, this is actually not just a property of p-B11 all fusion reactions in an IEC (i.e., D-D, D-He3, He3-He3) have that potential, but our current IEC technology falls very short of being able to tap the power in this way.
The lithium 6 and 7 isotopes are also direct conversion candidates. Most fusion reactions can make high energy charged particles, but typically only at about 20% or so of total fusion energy.
Boron 11 is 80% of naturally occurring boron, which is fairly abundant. Hydrogen is the most common element in the universe. The alphas produced by the reaction carry virtually all of the fusion energy and are tightly grouped in energy, making a simple direct conversion scheme possible. The system should run cleanly and efficiently on abundant fuel. What more can you ask?