  Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz
in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$,
$\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The
circularly polarized photons, produced from bremsstrahlung of longitudinally
polarized electrons, were tagged with the Glasgow magnetic spectrometer.
Charged pions and the decay photons of $\pi^0$ mesons were detected in a
$~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector
with the TAPS detector. The precisely measured asymmetries are very sensitive
to details of the production processes and are thus key observables in the
modeling of the reaction dynamics.
