The work is devoted to the study of the mixed convection in molten salt imitators with a magnetic field in application to promising power facilities, such as hybrid fusion plants. A comparison of direct numerical simulation by DNS with experimental data obtained with mixed convection of 20-30% KOH solution in a rectangular channel (round tube) under the influence of a coplanar (transverse) magnetic field is presented. Transient flow regimes (Re=3000-7000) and with more developed turbulence (Re=14000) were studied. The visualization of the boundary of the appearance of convective temperature pulsations arising due to magnetic effects depending on the regime parameters, such as the numbers Gr, Ha, Re, is presented. Data on the boundary are obtained on the basis of a combined analysis of experimental and numerical data on the modes of complete suppression of turbulence by a magnetic field and the development of high-amplitude pulsations. The possibility of experimental study of the occurrence boundary of fluctuations on the molten salt imitator from the point of view of the achievability of the regime parameters is evaluated. In particular, the possibility of implementing large Ha numbers by increasing the electrical conductivity of the imitators by increasing the temperature, KOH concentration in the solution, and increasing the geometric dimensions of the test section.