Re: Is plasma a better conductor than a superconducting wire?

There is no generic answer for the first question, it depends heavily on
which conditions both are used (for instance what temperature!). The only
absolute answer is that plasmas require high temperatures to exist. How
high depends on their density. Therefore, plasmas in the aurora have
temperatures of a few hundred degrees, while thermonuclear plasmas have
temperatures of hundred of millions of degrees. 

To give you an idea about how well they conduct electricity, a hydrogen
plasma similar to those existent in present-day tokamak experiments trying
to achieve fusion energy has an electrical resistivity slightly better than
that of pure copper (r_cu = 1.7E-8 ohm.meter, while for a hydrogen plasma
at a temperature of 15 million degrees r_plasma= 2.0 E-9 ohm.meter).
However, the performance of plasma as a conductor improves with temperature
very fast, so that it is many times a good approximation to assume it is a
perfect conductor. 

Superconductors, on the contrary, have (perfect) zero resistivity at very
small temperatures. But they are also limited in regard to the amount
current they can carry, since above some critical value for the current
superconductivity is destroyed (at least for many of them).

The main difference between them is that superconductors not only conduct
without dissipation, but they also "expulse" the magnetic field from within
them. A plasma, even if it also conducts without dissipation at very high
temperatures, "traps" the magnetic field within it, as if the field was frozen.


I hope this helps,

Raul Sanchez