  The reconstruction of the distribution function of runaway electrons (RE) in
magnetically confined fusion plasmas gives insights on the runaway electron
beam dynamics during plasma disruptions. In view of enabling a two-dimensional,
energy-pitch reconstruction of the RE velocity space, in this work we present a
calculation of the weight functions for the bremsstrahlung emission by the REs.
The weight functions allow bridging the bremsstrahlung spectrum with the RE
velocity space, as they tell the region of the velocity space that contributes
to a particular spectral measurement. The results are applied to investigate
the RE velocity-space sensitivity of the hard X-ray diagnostic installed at the
Joint European Torus.
