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Hard X-ray (HXR) sources are frequently observed near the top of solar flareloops, and the emission is widely ascribed to bremsstrahlung. We here revisitan alternative scenario which stresses the importance of inverse Comptonprocesses and the Kelvin- Helmholtz instability (KHI) proposed by Fang et al.(2016). This scenario adds a novel ingredient to the standard flare model,where evaporation flows from flare-impacted chromospheric foot-points interactwith each other near the loop top and produce turbulence via KHI. Theturbulence can act as a trapping region and as an efficient accelerator toprovide energetic electrons, which scatter soft X-ray (SXR) photons to HXRphotons via the inverse Compton mechanism. This paper focuses on the trigger ofthe KHI and the resulting turbulence in this new scenario. We perform aparameter survey to investigate the necessary ingredients to obtain KHI throughinteraction of chromospheric evaporation flows. When turbulence is produced inthe loop apex, an index of -5/3 can be found in the spectra of velocity andmagnetic field fluctuations. The KHI development and the generation ofturbulence are controlled by the amount of energy deposited in thechromospheric foot-points and the time scale of its energy deposition, buttypical values for M class flares show the KHI development routinely. Asymmetryof energy deposition determines the location where the turbulence is produced,and the synthesized SXR light curve shows a clear periodic signal related tothe sloshing motion of the vortex pattern created by the KHI.

Solar flares and Kelvin-Helmholtz instabilities: A parameter survey