  Dark current and multiple electron impacts (multipacting), as for example
observed in radio frequency (RF) structures of accelerators, are usually
harmful to the equipment and the beam quality. These effects need to be
suppressed to guarantee efficient and stable operation. Large scale simulations
can be used to understand causes and develop strategies to suppress these
phenomenas.
  We extend \opal, a parallel framework for charged particle optics in
accelerator structures and beam lines, with the necessary physics models to
efficiently and precisely simulate multipacting phenomenas. We added a
Fowler-Nordheim field emission model, two secondary electron emission models,
developed by Furman-Pivi and Vaughan respectively, as well as efficient 3D
boundary geometry handling capabilities. The models and their implementation
are carefully benchmark against a non-stationary multipacting theory for the
classic parallel plate geometry. A dedicated, parallel plate experiment is
sketched.
