Reply To: Peak Oil from Truth Out

[Di Vita]

“Di Vita, what do you make of Hannes Alfvén’s Nobel acceptance speech, repudiating magnetohydrodynamics wherein magnetic fields are assumed to be “frozen” into plasma?

Alfven’s speech provided Witalis and Turner with the physical basis of their dismissal of conventional magnetohydrodynamics (MHD) for plasmas whose linear size is smaller than the collisionless ion skin depth (the ion equivalent of the London depth in superconductors). Should a macroscopic description apply to such plasmas, it would rather be provided by the so called ‘extendend MHD’ (EMHD), which is known also as ‘electron MHD’ or ‘Hall MHD’. Ohm’s law is the fundamental difference between MHD and EMHD. If collisions are negligible, then MHD Omh’s law -together with Faraday’s law- predicts the magnetic field lines to be frozen to the velocity of the plasma, where the plasma is made of ions and electrons moving together. In contrast, if collisions are negligible then EMHD Ohm’s law and Faraday’s law predict the magnetic field lines to be frozen to the velocity of the electrons, which may differ from ion velocity. In other words, electrons and ions are much more decoupled in EMHD than in MHD. Remarkably, Stenzel’s experiments and Gekelmann et al.’s experiments have independently shown that spontaneous filamentation occurs in EMHD even without the triggering due to thermal instabilities predicted by Haines (in UK) in Z-pinch on the basis of MHD. Spontaneous filamentation is a well-known phenomenon in plasma guns like the magnetoplasmadynamic thruster (MPD), currently investigated in Japan, USA (prof. Choueiri) and Italy (prof. Andrenucci) for space electric propulsion. And, of course, it is the foundation of DPF operation, including LPPX. The very structure of DPF pinch is filamentary, as reported by Jakubowski et al. (in Poland) and by Bostick et al. (in USA). But the real amazing thing is tha DPF pinch filaments may collapse into relatively stable hot spots, which are non-filamentary, point-like, ultra-dense plasma structures. Nardi (in Italy) suggested that hot spots may indeed be just relaxed plasmas described by Taylor’s variational principle, according to which magnetic energy attains a minimum with the constraint of magnetic helicity (a quantity related to the twistedness of magnetic field lines). Unfortunately, Taylor’s principle provides no information concerning plasma density, while the only thing we know for sure about hot spots is that the density of electrons attains values near to the liquid water at room temperature and 1 bar. Finally, according to Brzosko (a Polish physicist working in the USA I met long ago in Dubrovnik), nuclear reactions occur spontaneously in hot spots and produce radionuclides. Qualitatively at least, old measurements of Harries in the USA agree with Brzosko’s measurements. These observations support LPPX roadmap towards fusion. Trouble is, occurence of such reactions within hot spots imply the magnetic field achieves locally values unheard-of so far on Earth. In turn, generation of such field is well understood in the framework of MHD. Indeed, Taylor’s principle is a matter of MHD, not of EMHD. But hot filaments and the resulting hot spots are definitely a matter of EMHD. If a macroscopic description of such structures is feasible (Nardi would disagree), then the role of electrons should be properly taken into account. This is precisely what Lerner’s original papers fail to do (according to my opinion). I have tried to take also electrons into account. Today, I think electrons dissipate a certain amount of energy initially stored in the ions. (After all, collisions are not negligible at high density). This dissipation, unaccounted for by Lerner, spoils fusion. However, I suggest there is some way to solve the problem: just recycle a fraction of the energy lost by the plasma through radiation, and fusion becomes again possible.