Intense relativistic electron beams (1 MV, 125 kA, 50 nsec) launched from foil and foilless diodes have been used to heat mirror‐confined hydrogen plasmas of density 2×1013and 1.6×1014cm−3. Electrical shorts in the foilless diodes were prevented by locating the diode outside the magnetic mirror in a region of lower plasma density. The plasma heating by the foilless diode was found to be slightly greater than that of the foil diode. This agrees qualitatively with the theory of Thode which predicts that foil scattering decreases the strength of the beam‐plasma interaction. E/T;8052.40.Mj, 52.50.Gj, 07.77.+p, 61.80.Fe