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 f lare plasma. This finding newly underlines an analogy between coronal and l aboratory plasma processes, The sawteeth occur during the impulsive flare p hase hard X-ray emission and consist of a sequence of almost identical narr ow band (deltaf/f similar or equal to 1%) drift bursts. All cases of our sa mple were associated with a radio emitting coronal shock wave (type II burs t). Similar oscillations are familiar in tokamak plasmas and understood as: signature of the kink instability of the toroidal current. We argue that t he radio sawteeth are nonthermal plasma emission due to 2-4% density fluctu ations of the flare plasma. The fluctuations can be excited by a current in stability 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.