  While detecting low mass exoplanets at tens of au is beyond current
instrumentation, debris discs provide a unique opportunity to study the outer
regions of planetary systems. Here we report new ALMA observations of the
80-200 Myr old Solar analogue HD 107146 that reveal the radial structure of its
exo-Kuiper belt at wavelengths of 1.1 and 0.86 mm. We find that the
planetesimal disc is broad, extending from 40 to 140 au, and it is
characterised by a circular gap extending from 60 to 100 au in which the
continuum emission drops by about 50%. We also report the non-detection of the
CO J=3-2 emission line, confirming that there is not enough gas to affect the
dust distribution. To date, HD 107146 is the only gas-poor system showing
multiple rings in the distribution of millimeter sized particles. These rings
suggest a similar distribution of the planetesimals producing small dust grains
that could be explained invoking the presence of one or more perturbing
planets. Because the disk appears axisymmetric, such planets should be on
circular orbits. By comparing N-body simulations with the observed visibilities
we find that to explain the radial extent and depth of the gap, it would be
required the presence of multiple low mass planets or a single planet that
migrated through the disc. Interior to HD 107146's exo-Kuiper belt we find
extended emission with a peak at ~20 au and consistent with the inner warm belt
that was previously predicted based on 22$\mu$m excess as in many other
systems. This warm belt is the first to be imaged, although unexpectedly
suggesting that it is asymmetric. This could be due to a large belt
eccentricity or due to clumpy structure produced by resonant trapping with an
additional inner planet.
