Sawtooth oscillations in solar flare radio emission

For the first time, we found a spectral fine structure of solar meter wave radio burst emission which can be due to sawtooth oscillations in the hot flare plasma. This finding newly underlines an analogy between coronal and laboratory plasma processes, The sawteeth occur during the impulsive flare phase hard X-ray emission and consist of a sequence of almost identical narrow band (deltaf/f similar or equal to 1%) drift bursts. All cases of our sample were associated with a radio emitting coronal shock wave (type II burst). Similar oscillations are familiar in tokamak plasmas and understood as: signature of the kink instability of the toroidal current. We argue that the radio sawteeth are nonthermal plasma emission due to 2-4% density fluctuations of the flare plasma. The fluctuations can be excited by a current instability in a coronal flare loop or in a vertical flaring current sheet e.g, occuring behind a rising magnetic flux rope. This is in analogy to kink instability effects observed in laboratory plasmas.