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Electron velocity distribution functions in the solar wind according tostandard models consist of 4 components, of which 3 are symmetric - the core,the halo, and the superhalo, and one is magnetic field-aligned, beam-likepopulation, referred to as the strahl. We analysed in-situ measurementsprovided by the two Helios spacecrafts to study the behaviour of the last, thestrahl electron population, in the inner Solar system between 0.3 and 1 au. Thestrahl is characterised with a pitch-angle width (PAW) depending on electronenergy and evolving with radial distance. We find different behaviour of thestrahl electrons for solar wind separated into types by the core electron betaparallel value ($\beta_{ec\parallel}$). For the low-$\beta_{ec\parallel}$ solarwind the strahl component is more pronounced, and the variation of PAW iselectron energy dependent. At low energies a slight focusing over distance isobserved, and the strahl PAW measured at 0.34 au agrees with the widthpredicted by a collisionless focusing model. The broadening observed forhigher-energy strahl electrons during expansion can be described by anexponential relation, which points toward an energy dependent scatteringmechanism. In the high-$\beta_{ec\parallel}$ solar wind the strahl appearsbroader in consistence with the high-$\beta_{ec\parallel}$ plasma being moreunstable with respect to kinetic instabilities. Finally we extrapolate ourobservations to the distance of 0.16 au, predicting the strahl PAWs in thelow-$\beta_{ec\parallel}$ solar wind to be $\sim$ 29$^o$ for all energies, andin the high-$\beta_{ec\parallel}$ solar wind a bit broader, ranging between37$^o$ and 65$^o$.

Scattering of Strahl Electrons in the Solar Wind between 0.3 and 1 au: Helios Observations