[en] Generally, analytical expressions for the growth rate of the Bunemann instability are given for small ratios of beam density n_b to plasma density n_p and are derived for zero applied electric field. In the case of this instability caused by runaway electrons, e.g. in the dense plasma focus or z-pinch, there exists an appreciable induced electric field strength and the assumption of n_b/n_p << 1 can no longer be made. In this report, a simplified dispersion relation including an applied, time-variable electric field is derived and an approximate analytical expression for the temporal growth rate is given. The magnetic field is assumed to be zero. (orig.)