Nonlinear acoustic effect of high-current electron beam at radiation rebuilding of metal target

The acoustic emission caused by high-current electron beam in massive polycrystalline metallic samples is studied. Under experiment conditions the bulk expansion of metal due to melting makes the main contribution into total volume increase under radiation heating, and determines the acoustic pulse amplitude. The latter increases with decreasing of crystalline grain dimensions in the region of the beam-target interaction. Size decrease of crystalline grains in metal takes place because of high-rate surface melting followed by fast hardening. Such structure rebuilding of a target material is brought off by the first pulse of the electron beam whereas the second and the following ones affect the target having the modified small-grain structure. The ratio N=(U)/U₁ of the mean stress amplitude (U) from the second and the following electron pulses to the amplitude U ₁ from the first one decreases from 2.6 (Nb) to 1.4 (Al). Such decrease is connected with the change of a sound generation mechanism