  The generation of magnetic flux in the solar interior and its transport from
the convection zone into the photosphere, the chromosphere, and the corona will
be in the focus of solar physics research for the next decades. With 4m class
telescopes, one plans to measure essential processes of radiative
magneto-hydrodynamics that are needed to understand the nature of solar
magnetic fields. One key-ingredient to understand the behavior of solar
magnetic field is the process of flux emergence into the solar photosphere, and
how the magnetic flux reorganizes to form the magnetic phenomena of active
regions like sunspots and pores. Here, we present a spectropolarimetric and
imaging data set from a region of emerging magnetic flux, in which a proto-spot
without penumbra forms a penumbra. During the formation of the penumbra the
area and the magnetic flux of the spot increases. First results of our data
analysis demonstrate that the additional magnetic flux, which contributes to
the increasing area of the penumbra, is supplied by the region of emerging
magnetic flux. We observe emerging bipoles that are aligned such that the spot
polarity is closer to the spot. As an emerging bipole separates, the pole of
the spot polarity migrates towards the spot, and finally merges with it. We
speculate that this is a fundamental process, which makes the sunspot
accumulate magnetic flux. As more and more flux is accumulated a penumbra forms
and transforms the proto-spot into a fully-fledged sunspot.
