  We analyzed a small flux rope eruption converted into a helical blowout jet
in a fan-spine configuration using multi-wavelength observations taken by SDO,
which occurred near the limb on 2016 January 9. In our study, first, we
estimated the fan-spine magnetic configuration with the potential field
calculation and found a sinistral small filament inside it. The filament along
with the flux rope erupted upward and interacted with the surrounding fan-
spine magnetic configuration, where the flux rope breaks in the middle section.
We observed compact brightening, flare ribbons and post-flare loops underneath
the erupting filament. The northern section of the flux rope reconnected with
the surrounding positive polarity, while the southern section straightened.
Next, we observed the untwisting motion of the southern leg, which was
transformed into a rotating helical blowout jet. The sign of the helicity of
the mini-filament matches the one of the rotating jet. This is consistent with
the jet models presented by Adams et al. (2014) and Sterling et al. (2015). We
focused on the fine thread structure of the rotating jet and traced three blobs
with the speed of 60-120 km/s, while the radial speed of the jet is approx 400
km/s. The untwisting motion of the jet accelerated plasma upward along the
collimated outer spine field lines, and it finally evolved into a narrow
coronal mass ejection at the height of approx 9 Rsun . On the basis of the
detailed analysis, we discussed clear evidence of the scenario of the breaking
of the flux rope and the formation of the helical blowout jet in the fan-spine
magnetic configuration.
