  Electron velocity distribution functions in the solar wind according to
standard models consist of 4 components, of which 3 are symmetric - the core,
the halo, and the superhalo, and one is magnetic field-aligned, beam-like
population, referred to as the strahl. We analysed in-situ measurements
provided by the two Helios spacecrafts to study the behaviour of the last, the
strahl electron population, in the inner Solar system between 0.3 and 1 au. The
strahl is characterised with a pitch-angle width (PAW) depending on electron
energy and evolving with radial distance. We find different behaviour of the
strahl electrons for solar wind separated into types by the core electron beta
parallel value ($\beta_{ec\parallel}$). For the low-$\beta_{ec\parallel}$ solar
wind the strahl component is more pronounced, and the variation of PAW is
electron energy dependent. At low energies a slight focusing over distance is
observed, and the strahl PAW measured at 0.34 au agrees with the width
predicted by a collisionless focusing model. The broadening observed for
higher-energy strahl electrons during expansion can be described by an
exponential relation, which points toward an energy dependent scattering
mechanism. In the high-$\beta_{ec\parallel}$ solar wind the strahl appears
broader in consistence with the high-$\beta_{ec\parallel}$ plasma being more
unstable with respect to kinetic instabilities. Finally we extrapolate our
observations to the distance of 0.16 au, predicting the strahl PAWs in the
low-$\beta_{ec\parallel}$ solar wind to be $\sim$ 29$^o$ for all energies, and
in the high-$\beta_{ec\parallel}$ solar wind a bit broader, ranging between
37$^o$ and 65$^o$.
