In plasma physics, the Lundquist number (denoted by S ) is a dimensionless ratio which compares the timescale of an Alfvén wave crossing to the timescale of resistive diffusion. It is a special case of the Magnetic Reynolds number when the Alfvén velocity is the typical velocity scale of the system, and is given by
S = L v A η , where L is the typical length scale of the system, η is the magnetic diffusivity and v A is the Alfvén velocity of the plasma.
High Lundquist numbers indicate highly conducting plasmas, while low Lundquist numbers indicate more resistive plasmas. Laboratory plasma experiments typically have Lundquist numbers between 10 2 − 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.
