Coherent Cherenkov radiation can be generated by "bunched" or rapidly rising charged-particle beams which propagate in a background magnetoplasma in which the Cherenkov conditions are satisfied. It is shown theoretically that when such an electron beam is injected into an initially non-ionized gas the power radiated and the plasma produced by the radiation exhibits a tangent-function dependence on time. This abrupt rise in the power level of the radiation is also shown to produce significant electron energy loss. Results from various high-intensity electron-beam experiments are compared with the theory. The tangent-function dependence of radiation growth and the energy loss of electrons have been observed.