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.
