On the boundary layer between a warm, streaming plasma and a confined magnetic field

Conditions are derived under which a magnetic field can be confined by a warm plasma composed of electrons and protons when the plasma has a bulk velocity parallel to the confined field. It is shown that unless the electrons have about 10³ as much thermal energy as the ions, it is extremely unlikely that an equilibrium state can exist. It is further shown that, in general, there will be a component of field normal to the confined field and also normal to its gradient and that if the plasma is not streaming, then a necessary, but not sufficient, condition for equilibrium is that this ‘extra’ field component be identically zero. It is suggested that this calculation may have some bearing on the state of the geomagnetic field-solar wind boundary, particularly on the tail side of the earth.