  Relativistic electron beam transport through a high-density, magnetized
plasma is studied numerically and theoretically. An electron beam injected into
a cold plasma excites Weibel and two-stream instabilities that heat the beam
and saturate. In the absence of an applied magnetic field, the heated beam
continues to propagate. However, when a magnetic field of particular strength
is applied along the direction of beam propagation, a secondary instability of
off-angle whistler modes is excited. These modes then couple nonlinearly
creating a large amplitude parallel propagating whistler that stops the beam.
In this letter, we will show the phenomena in detail and explain the mechanism
of whistler mediated beam stagnation.
