Hey Dave… have you read LLP’s writings on how the Quantum Magnetic Field effect is supposed to mitigate the losses to Brem? The X-rays are pretty significant with fusing just isotopes of hydrogen, but when you start trying to fuse Boron, things get really difficult. Boron has 5 times the charge of hydrogen and about 25 times the effect of braking the electrons (bremmstralung) which cools the plasma. But the QMF should kick in if the field strength gets high enough.

A lot of the objections you’ve noted don’t quite apply to pulsed power devices like Focus Fusion. Certainly to a tokamak, and somewhat still in a polywell. But LLP’s approach has the benefit of being only a couple dozen nano seconds long. Which can avoid many of the causes of plasma cooling. Also, since the energy is going to be extracted as direct electricity and captured x-rays… it is not so much a question of the temperature gradient.

Every fusion approach has it’s problems. With MCF, the science is proven, but the engineering may make it impractical for economic reasons. But I would not ever say the word, “impossible”. Just that Materials Science and other adjacent technology needs a lot of catching up first.

I really like how transparent Focus Fusion has been compared to the other innovative confinement concepts. Polywell has to be mostly hush because of the Navy funding though, so maybe they are making better progress than we know. But it seems like Lerner has been making great progress. The biggest challenges so far have been engineering problems. But what I like best is that they will know whether pB11 fusion using a Focus Fusion pinch is feasible within a year. If it is proven to be feasible, and they demonstrate some level of fusion using pB11… then the eyes, and pockets, of the world would be opened for them. 🙂

The way I see it is that you don’t consider the bremsstrahlung x-ray radiated as losses. There will be some other radiative losses that you can’t recover but if the onion works as well as is hoped a significant (>70%) of the x-ray energy in the 10-30keV range could be recovered.

The key issue for getting a reasonable fusion burn in the plasmoids is that the x-ray cooling is not so high as to cool the plasma faster than the fusion energy from the fast He-4 products can be redistributed in the plasma keeping it hot.

The initial tests with DD done so far have shown the radiative losses are not so high, such then the heating during the pinch can get the plasma hot enough for pB11 ignition (but at lower densities).

The next test is to repeat that temperature threshold with higher Z gases where traditionally the Z^2 dependence of the bremsstrahlung would mean the cooling will be much faster.

Todd Rider’s thesis http://dspace.mit.edu/handle/1721.1/11412 and subsequent work, showed that this bremsstrahlung issue effectively rules out all other fusion fuels except D+T, D+D, and D+He-3, and furthermore for nett gain has to be at or near thermal equilibrium. This is partly why I don’t believe any of the other innovative concepts such as polywells will work. However Rider did not take account of the effect of the quantization of electron cyclotron orbits in very strong magnetic fields http://en.wikipedia.org/wiki/Landau_quantization. This limits the transfer of energy from the fast ions to the electrons, and effectively keeps the electron temperature much lower than the ion temperature. Even so it is a tall order to reach the extreme fields needed to reduce the key collision parameter known as the Coulomb Logarithm from the standard value of 15-20 beyond even Rider’s most optimistic value of 5.

Joe:

Hybrid Mmagnets (Combination of superconducting magnets and normal magnets) hold records of 100 T or 1E6 Gauss in a pulse mode. Pulse current drivers like the plasma focus and Z-pinch are one of the few methods to produce such strong fields in a somewhat controlled way. Other methods are explosively driven like nuclear detonations. Annually, a meeting is held on Megagauss fields which are common in the Z-pinch community using 1 MA to 24 MA drivers to report results on 1E7 and 1E8 Gauss experiments. The reproducible demonstration of Gigagauss fields had yet to be shown. The Focus Fusion concept argues they are necessary but making a measurement of these fields directly is very challenging. Diagnostics are only now becoming available to do what is needed and they require very specific axillary facilities that are likely to exceed the cost of FoFu-1. It is likely that Gigagauss fields will be inferred from another measurement before directly measured. The problem with measurement by inference is the interpretation. Someone sees a plasmoid while others see a Rayleigh-Taylor neck or so called hot spots. To achieve a Gigagauss field using a 1 MA drive pulse, you need a pinch diameter of ~2 microns. Typical observed pinch diameter are more like 5 millimeters. The problem is more complex than this simple calculation but features less than 10 microns are required to achieve such a high field unless you are using other techniques like flux compression.

Dave:

Black body losses are not that significant in a deuterium plasma because most of the electrons are unbound leading so-called free-free radiation instead of free-bound radiation. Free-bound transitions are more frequent and generally more potent because you can excite a bound electron leading to a photon emission to return to ground. It can be rapidly excited again. In the free-free mode, you need specific interactions to generate radiation. Also, deuterium plasma is optically thin. Remind your engineer friends that a black body is the most efficient emitter of radiation at a given temperature which means it takes the most power to sustain a black body at a given temperature. Gray body and white bodies (optically thin bodies) are much easier to heat to high temperature given a fixed power input. Emissivity for plasma can be quite low or large depending upon the conditions of interest. This is a complex matter is plasma physics requiring very complex diagnostics and very intricate numerical simulations.

I would add to Jamesr’s comment about brems. Brems emission is typically related to electron temperature or energy. In pinch devices, the electron temperature is naturally lower than the ion temperature. It is commonly reported in published literature since 1958. Pinch plasma is one of the few plasma types to have hotter ions than electrons. That is a huge advantage to accessing p+11B fuel. If you can further suppress the electron temperature or increase the ion temperature using strong magnetic fields, you can benefit further.