  An algorithm is demonstrated that performs first-principles tracking of
relativistic charged-particles. A covariant approach is used which relies on
retarded vector potentials for trajectory integration instead of performing
electromagnetic field calculations. When accounting for retardation effects,
the peak vector potential and corresponding Lorentz force in the direction of
travel increase asymptotically for high-$\beta$ particles. This produces a very
strong field distribution at small angles from the particle's direction of
travel, which can result in considerable change in momentum when approaching a
conducting surface or another charged particle. We quantify the former effect
for protons and electrons at various energies and aperture sizes, where
substantial power deposition can be avoided by ensuring that particles do not
pass within roughly 10 microns of the aperture surface.
  We also simulate breaking a test particle's line of sight with a conductor or
other charged body. After this instant, the test particle continues to
accelerate due to residual fields, but no longer produces an opposing force on
any charged or conducting object; thus any recoil on the enclosing structure is
effectively reduced.
  Resulting acceleration dynamics are characterized using protons and electrons
at various energies; with, for example, a 1% energy gain for an 85 MeV electron
traversing its reflected wake while approaching a pinhole aperture. We then
integrate a micro-scale dielectric laser acceleration (DLA) device into our
simulations: compared with a solitary 2 mm DLA, we find a factor of two
increase in energy gain when combining the DLA with a series of
conducting-surface choppers.
