  We report on the successful experimental generation of electron bunches with
ramped current profiles. The technique relies on impressing nonlinear
correlations in the longitudinal phase space using a superconducing
radiofrequency linear accelerator operating at two frequencies and a
current-enhancing dispersive section. The produced $\sim 700$-MeV bunches have
peak currents of the order of a kilo-Amp\`ere. Data taken for various
accelerator settings demonstrate the versatility of the method and in
particular its ability to produce current profiles that have a quasi-linear
dependency on the longitudinal (temporal) coordinate. The measured bunch
parameters are shown, via numerical simulations, to produce gigavolt-per-meter
peak accelerating electric fields with transformer ratios larger than 2 in
dielectric-lined waveguides.
