Magnetic flux area S is where "B" is the magnitude of the magnetic field (the magnetic flux density) having the unit of Wb/m (tesla), "S" is the area of the surface, and "θ" is the angle between the magnetic field lines and the normal (perpendicular) to S. For a varying magnetic field, we first consider the magnetic flux through an infinitesimal area element dS, where we may consider the field to be constant: A generic surface, S, can then be broken into infinitesimal elements and the total magnetic flux through the surface is then the surface integral From the definition of the
Flux tube density of the tube increase with the same proportionality. If a flux tube with a configuration of a magnetic field of B and a plasma density of ρ confined to the tube is compressed by a scalar value defined as λ, the new magnetic field and density are given by:formula_10formula_11If λ < 1, known as traverse compression, B and ρ increase and are scaled the same while transverse expansion decreases B and ρ by the same value and proportion where B/ρ = constant value. Extending the length of the flux tube by λ* gives a new length of L =