  We examine the momentum and angular momentum (including spin) properties of
linear waves, both longitudinal (Langmuir) and transverse (electromagnetic), in
an isotropic nonrelativistic collisionless electron plasma. We focus on
conserved quantities associated with the translational and rotational
invariance of the wave fields with respect to the homogeneous medium; these are
sometimes called pseudo-momenta. There are two types of the momentum and
angular momentum densities: (i) the kinetic ones associated with the energy
flux density and the symmetrized (Belinfante) energy-momentum tensor and (ii)
the canonical ones associated with the conserved Noether currents and canonical
energy-momentum tensor. We find that the canonical momentum and spin densities
of Langmuir waves are similar to those of sound waves in fluids or gases; they
are expressed via the electron velocity field. In turn, the momentum and spin
densities of electromagnetic waves can be written either in the forms known for
free-space electromagnetic fields, involving only the electric field, or in the
dual-symmetric forms involving both electric and magnetic fields, as well as
the effective permittivity of plasma. We derive these properties both within
the phenomenological macroscopic approach and microscopic Lagrangian field
theory for the coupled electromagnetic fields and electrons. Finally, we
explore implications of the canonical momentum and spin densities in transport
and electrodynamic phenomena: the Stokes drift, the wave-induced magnetization
(inverse Faraday effect), etc.
