  Previous studies on the beam-driven plasma emission process were done mainly
for unmagnetized plasmas. Here we present fully-kinetic electromagnetic
particle-in-cell simulations to investigate such process in weakly-magnetized
plasmas of the solar corona conditions. The primary mode excited is the
beam-Langmuir (BL) mode via the classical bump-on-tail instability. Other modes
include the whistler (W) mode excited by the electron cyclotron resonance
instability, the generalized Langmuir (GL) waves that include a superluminal
Z-mode component with smaller wave number $k$ and a thermal Langmuir component
with larger $k$, and the fundamental (F) and harmonic (H) branches of plasma
emission. Further simulations of different mass and temperature ratios of
electrons and protons indicate that the GL mode and the two escaping modes (F
and H) correlate positively with the BL mode in intensity, supporting that they
are excited through nonlinear wave-wave coupling processes involving the BL
mode. We suggest that the dominant process is the decay of the primary BL mode.
This is consistent with the standard theory of plasma emission. Yet, the other
possibility of the Z+W$\rightarrow$O--F coalescing process for the F emission
cannot be ruled out completely.
