Monday, October 01, 2007

New Sidebar Links, And The Determinism Of Pessimism

Three new sidebar links (and some culling of older ones, which I didn't document): IEC Fusion Technology, itself an offshoot of Power And Control, which I linked to about a month ago; and Talk-Polywell, which mostly is a bunch of guys praying Robert Bussard is right and Todd Rider is wrong.

On this subject, FuturePundit recently ran a piece about the former chairman of Shell, Lord Oxburgh, admitting peak oil production will occur within the next 20 years. What was interesting was the ensuing comments section, and in particular, Paul Dietz' comments about Bussard's reactor:

It cannot prevent electron-ion interactions. Let me run you through the argument to illustrate the two horns of the dilemma.

Polywell has a putative central interaction region where the ions are energetic and are to undergo nuclear reactions. This interaction region CANNOT exclude electrons. If it did (assuming it even could), the space charge of the ions would limit the ion density to a low value, preventing anywhere close to practical (let alone the promised 100 MW!) power levels.

So, there are electrons in this region. There are two possibilities: the electrons have energies approaching those of the ions ('hot' electrons) or the electrons are significantly less energetic ('cold' electrons).

In the first case, bremsstrahlung power exceeds fusion power.

In the second case, the rate of energy transfer from the ions to the electrons greatly exceeds fusion power. This power would have to be recovered and reinjected with extremely high efficiency. Rider's thesis, IIRC, showed that if the electron temperature were half that of the ions, the recirculating power would exceed the fusion power by a couple of orders of magnitude.

These two cases overlap; in the intermediate energy case both occur.

Re-reading Todd Rider's doctoral thesis "Fundamental limitations on fusion systems not in equilibrium" (note to self: link off the Polywell Wikipedia page — the damn thing keeps moving), it seems a complex net of impossibilities. Want to use a magnetic trap to keep electrons away from the ions? Then you induce synchrotron radiation. And then there's the thermalization problem, which, as far as I can understand it, means the ions will need so much energy to keep them inside the device that, unless you're very very efficient about getting them back in, you'll lose them to the outside of the box before they have a chance to fuse.

Rider, of course, seems to have gone on to become a biomedical researcher, a choice maybe not surprising considering the hopelessness invested in his doctoral dissertation. Maybe he's right, but I do have to ask a hopefully useful question: what was the role of his thesis advisor was in drawing those conclusions? Overseeing Rider's project was Lawrence Lidsky, a long-time MIT fusion researcher who wrote a seminal 1983 paper entitled, "The Trouble With Fusion". Despairing of ever surmounting the engineering challenges, he gave up on fusion altogether, and one wonders just how much that colored Rider's research and paper.

Contradicting Rider: "Maxwell Don't Live Here" claims to have a bunch of answers to why IEC fusion could actually work, bolstered by some recent research at MIT.

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