We consider the effects of the heat balance on the structural stability of a preflare current layer. The problem of small perturbations is solved in the piecewise homogeneous magnetohydrodynamic (MHD) approximation taking into account viscosity, electrical and thermal conductivity, and radiative cooling. Solution to the problem allows for the formation of an instability of thermal nature. There is no external magnetic field inside the current layer in the equilibrium state, but it can penetrate inside when the current layer is disturbed. The formation of a magnetic field perturbation inside the layer creates a dedicated frequency in a broadband disturbance subject to thermal instability. In the linear phase, the growth time of the instability is proportional to the characteristic time of radiative cooling of the plasma and depends on the logarithmic derivatives of the radiative cooling function with respect to the plasma parameters. The instability results in transverse fragmentation of the current layer with a spatial period of 1–10 Mm along the layer in a wide range of coronal plasma parameters. The role of that instability in the triggering of the primary energy release in solar flares is discussed.

我们考虑了热平衡对预扩电流层结构稳定性的影响。在考虑粘度，电导率和导热率以及辐射冷却的情况下，通过分段均相磁流体动力学（MHD）逼近解决了小扰动的问题。该问题的解决方案允许形成热性质的不稳定性。处于平衡状态的电流层内部没有外部磁场，但是当电流层受到干扰时，它可以穿透内部磁场。在该层内部形成磁场扰动会在宽带扰动中产生一个专用频率，该扰动会受到热不稳定性的影响。在线性阶段 不稳定性的增长时间与等离子辐射冷却的特征时间成比例，并且取决于等离子辐射冷却功能的对数导数。这种不稳定性会导致当前层的横向破碎，在各种冠状等离子体参数范围内，沿该层的空间周期为1-10 Mm。讨论了这种不稳定性在引发太阳耀斑一次能量释放中的作用。