  A high energy density plasma embedded in a neutral gas is able to launch an
outward-propagating nonlinear electrostatic ionization wave that traps
energetic electrons. The trapping maintains a strong sheath electric field,
enabling rapid and long-lasting wave propagation aided by field ionization.
Using 1D3V kinetic simulations, we examine the propagation of the ionization
wave in the presence of a transverse MG-level magnetic field with the objective
to identify qualitative changes in a regime where the initial thermal pressure
of the plasma exceeds the pressure of the magnetic field ($\beta>1$). Our key
finding is that the magnetic field stops the propagation by causing the
energetic electrons sustaining the wave to lose their energy by emitting an
electromagnetic wave. The emission is accompanied by the magnetic field
expulsion from the plasma and an increased electron loss from the trapping wave
structure. The described effect provides a mechanism mitigating rapid plasma
expansion for those applications that involve an embedded plasma, such as
high-flux neutron production from laser-irradiated deuterium gas jets.
