epsilon_0       = 8.85418782e-12 # Permittivity of free space
mu_0            = 1.25663706e-7  # Permeability of free space
speed_of_light  = 2.99792458e8   # Speed of light in vacuum
charge_electron =-1.60217663e-19 # Electron charge
charge_proton   = 1.60217663e-19 # Proton charge
mass_electron   = 9.10938371e-31 # Electron mass
mass_proton     = 1.67262193e-27 # Proton mass
q_m_electron    = charge_electron / mass_electron # Electron charge-to-mass ratio
q_m_proton      = charge_proton   / mass_proton   # Proton charge-to-mass ratio
