[en] This paper reports on the study of the physics of thermonuclear reaction products-alpha particles in fusion devices. During the 1960s, solving alpha-particle problems was far from a practical necessity; therefore, their investigation was carried out by small groups of theorists who optimistically estimated the rate of progress toward a fusion reactor and believed that many important and interesting effects are connected with alpha particles. During the progress in fusion experiments, especially on tokamaks, the scope of alpha-particle research broadened. Also, the range of problems considered essentially increased. Research has now reached a stage in which a comprehensive analysis of alpha-particle influence on reactor operations is a necessity. Ths necessity is caused both by the projected reactors and by the requirements of planning experiments on existing large tokamaks with deuterium-tritium plasma. This is why the study of alpha-particle physics is part of a series of the most important developments in modern fusion programs