Reply To: The Harmful Economics of Biofuels

[jamesr]

Henning wrote: Electrons fly off in the other direction than alpha particles, because of the magnetic field (right-hand rule).

It’s not the magnetic field directly. As far as I understand it, it is when the concentrated magnetic field created by the pinch collapses, the rapid change in magnetic field creates an electric field by Faraday’s law dB/dt=-curl(E).

The symmetry of the highly curved magnetic field creates the electric field such that it is directed along the axis of the DPF, accelerating the ions in a cone of around 6degrees away from the anode and the electrons in the opposite direction. However, the electrons have much lower inertia and as they start to be accelerated scatter off ions transferring some of their energy to them, before starting to accelerate down the E-field again. So rather than being able to build up into a coherent beam, a large fraction of the electrons don’t make it out of the plasmoid. Some do make it out and are accelerated enough to blast a little pit in the anode.

After the collapse of the field the plasma will of course react to re-establish quasi-neutrality where any imbalance has built up, but this is on a longer timescale.

It is also worth reiterating the formation of the beam of ions is nothing to do with the fusion or alpha particle directions. Ion beams are created in all DPF’s that manage to form a strong pinch, even with un-reactive gasses. Any fusion alphas (or other charged products in the case of other reactions), which although initially moving much faster than the rest of the ions in the plasma are still confined by the magnetic field of the plasmoid. It will take them roughly 20 collisions to dump most of that kinetic energy and thermalise with the rest of the plasma (heating it in the process) but this occurs on the pico-second timescale rather than the tens of nanosecond lifetime of the plasmoid.