Alfven Velocity Calculator

Your details

Choose which quantity to solve for. The other two become the known inputs.
Magnetic flux density of the background field threading the plasma. 1 T = 10,000 G.
Mass per unit volume of the plasma. For a proton plasma, rho = n_i * m_proton.
Background plasma bulk flow speed. Used to compute the Alfven Mach number.
Thermal pressure of the plasma, used to compute plasma beta. Leave zero to skip.
Pa
Ion species determines the ion inertial length. Proton is the standard choice for solar-wind plasma.
Alfven velocitySuper-Alfvenic flow
44,603.1029m/s

Speed of Alfven wave propagation along the magnetic field

Alfven velocity44.603km/s
Fraction of speed of light0.0149%
Plasma beta0
Alfven Mach number11.21
Ion inertial length9.3128m
Magnetic pressure0.001Pa
0.0149 % of c
Slow plasma<0.1Moderate speed0.1-1Fast plasma1-2.5Relativistic2.5+

Alfven velocity: 44.6 km/s (0.0149% of c)

  • The Alfven wave travels at 44.6 km/s, which is 0.015% of the speed of light.
  • Plasma beta is 1.01e-7: the magnetic field dominates thermal pressure by a large margin. This is the low-beta regime common in the solar corona and tokamaks.
  • The plasma flow is super-Alfvenic with Alfven Mach number M_A = 11.210.
  • Ion inertial length is 9.31 m. At scales smaller than this, the Hall effect becomes important and the simple MHD approximation breaks down.

Next stepCompare the Alfven velocity to your flow speed to determine whether Alfven waves can propagate upstream against the flow.

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