Cosmic Capacitors - Nov 11 2010

[mharratsc]

Think about it in the simplest (i.e. "Mike-speed" form):

Discharge occurs when threshhold is exceeded and the dielectric conducts, right?

Is it any different when a double-layer finally pops, really?

Seems simple on the face of it, but I'm not exactly providing the model, predictions, and equations that some folks here might want to see regarding my thoughts on the matter. o.O

[solrey]

Some links with math and theory relating to the dielectric properties of plasma.

Space Dispersive Properties of Plasma

Generalized dispersion relation for electron Bernstein waves in a non-Maxwellian magnetized anisotropic plasma

Ionospheric Physics of Radio Wave Propagation

Dielectric constant of a plasma

We now need to consider how we could transmit information through a plasma (or any other dielectric medium) by means of electromagnetic waves.

Dielectric constant of a collisional plasma

Theory of the dielectric constant of a partially ionized plasma

cheers

[jjohnson]

Even if capacitors don't exist or are not very strong in space plasma (a thesis I disagree with, but continuing) there is another mechanism for storing and releasing energy, and that is the magnetic field of an inductor, or the self-inductance of the circuit.

Dr. Paul Bellan, CalTech, invokes this argument in Fundamentals of Plasma Physics in discussing kink instabilites in 9.6. To paraphrase, if flux (current flow) is to be conserved in a highly conductive plasma circuit, the magnetic energy will be lowered by any (topological or morphological) rearrangement of the circuit that increases self-inductance. The (Bennett) pinch force is consistent with this as the inductance of a conductor depends inversely on its radius. The hoop force is also consistent with this since inductance of a current loop increases with the major radius of the loop. This drive to minimize energy while conserving flux can results in the kink instability.

The kink instability develops when current flowing "locally, anyway) in a straight line develops an instability that causes the current path to become helical. This coiled current is not unlike the winding of a simple toroid, so the current then has more inductance than the former straight length, he argues, so the effect of the kink instability acts to increase the self-inductance of the circuit.

Peratt shows in 2.9.2 that a cold plasma current beam propagating through background plasma conditions can become unstable and propagation "as a beam" terminates as kink instabilities in the wavefront develop. Part of the kinetic energy of the kinking beam electrons is transferred to the surrounding plasma electrons, causing the background plasma to be heated. He models a beam with a density of 1 particle per cc (10^6 per cubic meter)and radius 100 km into a space 300 by 1000 km, showing in Figure 2.17 the instability growth and the varying radii in the vicinity of the kink. The heating increases with the number of charged particles in the beam; i.e. as the amperage of the current is increased in the simulation. At the scale where the current is as high as 86 000 amps (beam nearly relativistic) plasma electrons can attain energies as high as 1.5MeV. Kink instabilities thus are seen as bright areas as the heated plasma radiates the energy transferred from the beam current.

Having inductance in a circuit is another way of releasing and storing energy. Whether oscillating circuit phenomena can be derived in this way from plasma circuitry, I don't know. So far it looks to a layman like the capacitance of double layers may be more efficient than the inductance discussed above. Sounds to me like a good excuse for a grant!

[genogeno1]

At the risk of sounding like a total newbie to all this, and realizing this is a late posting to an old thread, I thought that all you needed was the differential movement between two or more magnetized plasma layers to generate current. I was a little confused as to Nereids comment about the capacitor issue.