This paper discusses the temperature distribution in the accelerating structure of a 20MeV electron linac designed for medical use. An examination is made of the quality of the concrete structure and the cooling mode (of U-type) adopted in this linac. On the basis of the formulas of temperature distribution drawn from the discussion
a comparison concerning effect is given between two cooling modes
the U-type mentoned above and the unidirection flow type as adopted in some other linacs.