  A new computational model is presented suitable for exploring the
self-consistent production of energetic electrons during magnetic reconnection
in macroscale systems. The equations are based on the recent discovery that
parallel electric fields are ineffective drivers of energetic particles during
reconnection so that the kinetic scales which control the development of such
fields can be ordered out of the equations. The resulting equations consist of
a magnetohydrodynamic (MHD) backbone with the energetic component represented
by macro-particles described by the guiding center equations. Crucially, the
energetic component feeds back on the MHD equations so that the total energy of
the MHD fluid and the energetic particles is conserved. The equations correctly
describe the firehose instability, whose dynamics plays a key role in
throttling reconnection and in controlling the spectra of energetic particles.
The results of early tests of the model, including the propagation of Alfven
waves in a system with pressure anisotropy and the growth of firehose modes,
establish that the basic algorithm is stable and produces reliable physics
results in preparation for further benchmarking with particle-in-cell models of
reconnection.
