  Solar flare electron acceleration is an extremely efficient process, but the
method of acceleration is not well constrained. Two of the essential
diagnostics: electron anisotropy (velocity angle to the guiding magnetic field)
and the high energy cutoff (highest energy electrons produced by the
acceleration conditions: mechanism, spatial extent, time), are important
quantities that can help to constrain electron acceleration at the Sun but both
are poorly determined. Here, using electron and X-ray transport simulations
that account for both collisional and non-collisional transport processes such
as turbulent scattering, and X-ray albedo, we show that X-ray polarization can
be used to constrain the anisotropy of the accelerated electron distribution
and the most energetic accelerated electrons together. Moreover, we show that
prospective missions, e.g. CubeSat missions without imaging information, can be
used alongside such simulations to determine these parameters. We conclude that
a fuller understanding of flare acceleration processes will come from missions
capable of both X-ray flux and polarization spectral measurements together.
Although imaging polarimetry is highly desired, we demonstrate that
spectro-polarimeters without imaging can also provide strong constraints on
electron anisotropy and the high energy cutoff.
