  Developing particle-in-cell (PIC) methods using finite element basis sets,
and without auxiliary divergence cleaning methods, was a long standing problem
until recently. It was shown that if consistent spatial basis functions are
used, one can indeed create a methodology that was charge conserving, albeit
using a leap-frog time stepping method. While this is a significant advance,
leap frog schemes are only conditionally stable and time step sizes are closely
tied to the underlying mesh. Ideally, to take full advantage of advances in
finite element methods (FEMs), one needs a charge conserving PIC methodology
that is agnostic to the time stepping method. This is the principal
contribution of this paper. In what follows, we shall develop this methodology,
prove that both charge and Gauss' laws are discretely satisfied at every time
step, provide the necessary details to implement this methodology for both the
wave equation FEM and Maxwell Solver FEM, and finally demonstrate its efficacy
on a suite of test problems. The method will be demonstrated by single particle
evolution, non-neutral beams with space-charge, and adiabatic expansion of a
neutral plasma, where the debye length has been resolved, and real mass ratios
are used.
