function describing the particle density of a plasma in 6-D space made up of the three spatial vectors and the three velocity vectors, with units s3 m-6
NOTE For distributions that are spatially uniform and isotropic, it is often quoted as f(v), a function of scalar velocity, with units s m-4, or f(E) a function of energy, with units J-1m-3. This can be converted to flux as follows:
v is the scalar velocity
E is the energy
m is the particle mass.