Potential of the test particle in the magnetic field I

The problem of the test particle potential in the external homogeneous magnetic field is solved in the unmagnetized plasma. It is shown that for the case when the parallel component velocity of the test particle is greater than the thermal velocity of the background particles, the potential has the Coulomb character while for the case where the parallel component velocity is less than the thermal velocity the potential is of Debye character. The Larmor radius of the test particle appears as a additional parameter in these potentials.