Lundquist number

In plasma physics, the Lundquist number (denoted by $S$) is the dimensionless ratio of an Alfvén wave crossing timescale to a diffusion timescale. In SI units, it is given by:$Sequivfrac\{mu\_0LV\_A\}\{eta\}$,where $L$ is a typical length scale, $mu\_0$ is the permeability of free space, $V\_A=frac\{B\}\{sqrt\{mu\_0\; ho$ is the Alfvén speed, and $eta$ is the plasma resistivity. High Lundquist numbers indicate highly conducting plasmas, while low Lundquist numbers indicate more resistive plasmas. Laboratory plasma experiments typically have Lundquist numbers between $50-10^8$, while in astrophysical situations the Lundquist number can be greater than $10^\{20\}$. Considerations of Lundquist number are especially important in magnetic reconnection.

References

* Eric Priest, Terry Forbes, "Magnetic Reconnection", Cambridge University Press 2000, ISBN 0521481791, [http://assets.cambridge.org/0521481791/sample/0521481791WSN01.pdf contents and sample chapter online]