  Electrostatic solitary structures are generated by injection of a
suprathermal electron beam parallel to the magnetic field in a laboratory
plasma. Electric microprobes with tips smaller than the Debye length
($\lambda_{De}$) enabled the measurement of positive potential pulses with
half-widths 4 to 25$\lambda_{De}$ and velocities 1 to 3 times the background
electron thermal speed. Nonlinear wave packets of similar velocities and scales
are also observed, indicating that the two descend from the same mode which is
consistent with the electrostatic whistler mode and result from an instability
likely to be driven by field-aligned currents.
