Sorry, no. IEC systems, while they do have a very slight charge imbalance, nevertheless do still satisfy the "quasineutrality" condition to an excellent degree of approximation, as shown by Rider in his thesis.Well in a perfectly neutral system. Bremmsstrahlung is proportional to electron density, electron temperature, and the ratio of electrons to ion Z. These virtual cathode systems are by definition not perfectly neutral, as the electron/ion ratio > 1 sets up the electrostatic well.gdp said:...I am extremely skeptical of this claim by Nebel. Bremsstrahlung scales as the square of the ion charge, so bremsstrahlung off Boron is 25 times worse than bremsstrahlung off D or T, and six times worse than bremsstrahlung off He3.
I am still very skeptical, and I'd want to see the data. IIRC, Rider explicitly shows that in a quasineutral plasma, the bremsstrahlung loss rate and fusion power depend on the densities of the ion species in the exact same way, so that the ratio of bremsstrahlung losses to fusion gain is a constant, independent of any monkey-business with the ion mixture. Anything that decreases bremsstrahlung losses should therefore decrease the fusion power by the exact same fraction.mheslep said:Only to a point, as Nebel suggested with the 'optimum' qualifier, as the power gain function is not linear in all its parameters.gdp said:Since the fusion power scales as the product of the proton and boron ion densities, trying to beat bremsstrahlung by running a "lean mix" (lowering the boron ion concentration relative to the proton concentration) necessarily also decreases the output power, so it is a self-defeating strategy.
Has Nebel published any of these claims in a refereed journal, or is it the only source for Nebel's claims the blog exchange between Nebel and Carlson?
Rider deals with this. In effect, one is "refrigerating" the electrons by removing them from the system before they can equilibriate. Since the electrons are "cold" compared to the ions, the ions therefore continuously lose energy to the cold electrons through coulomb collisions, producing entropy, and requiring that additional power be recycled to maintain the ion distribution. Rider finds that the power expended to maintain the disequilibrium will exceed the additional gain from operating at disequilibrium.mheslep said:As I understand it, though Rider/Nevins correctly point out the 2nd law issues in play, there are two areas where they fall short: 1) the electron confinement times for a virtual cathode device are shorter than the thermalization/collision time with ions so that the electron temperature never has the opportunity to rise enough to cause unsustainable Bremmstrahlung,gdp said:Red Herring. The 2nd Law limit on IEC comes from the necessary disequilibrium between the electron and ion distributions --- not from the secondary disequilibrium between ion species. Two-stream instability is a collective effect that increases the thermalization rate of the plasma --- but even if two-stream and other instabilities were somehow completely eliminated, the unavoidable coulomb collisions between the electrons and ions will still cause their energy distributions to relax toward equilibrium with each other, generating entropy during the process. To maintain the electron/ion disequilibrium will cost power. Rider shows that maintaining this disequilibrium will cost more power than will be gained from operating at an electron/ion disequilibrium.
There is no escape from the 2nd Law.
I have downloaded the paper, but have not yet had time to read it. However, I note already that according to their abstract, they are performing an "optimistic" (their term!) calculation that explicitly neglects electron-ion collisional interactions --- and neglecting electron-ion interactions is simply not physically realistic in these disequilibrium systems.mheslep said:2) their mathematical treatment of collisionality is inadequate. That is, the FP model performed by Chacon et al 2000 improves power gain (Q) by 5 to 10x over that predicted by Nevins. Take this last part up with Chacon et al.
Even worse, they appear to be treating the electron distribution as a fixed, prescribed "background" that generates a potential-well of two assumed forms: square-well and parabolic --- neither of which are particularly physical.
It is like attempting to estimate the performance of an automobile by neglecting road and air friction, and concluding that top speeds of 900 mph should be possible. Well, of course you can get unphysically good results, if you throw away the most important physical limiting factors!
A truly "self-consistent" calculation of fusion gain in an IEC device will need to explicitly treat the continuous transfer of energy from the ion to the electron population, rather than ignoring collisions and treating the electron population as merely a fixed prescribed background that is unaffected by the ion population as Chacon and Miley appear to be doing in their paper.