In this work we present Thomson scattering measurements on a nanosecond pulsed high voltage dielectric barrier discharge (DBD)-like helium plasma jet, operated in ambient air. With the low detection limit offered by a triple grating spectrograph equipped with a high quantum efficiency intensified charge-coupled device (ICCD) camera, temporally and spatially resolved electron densities and mean energies have been mapped. 7¿kV peak with 250¿ns width pulses at 20¿kHz are applied to the inner cylindrical shaped electrode of a DBD. This results in a peculiar hollow electron density profile in the vicinity of the jet nozzle with maximum values of ne = 5 × 1018¿m-3 and mean energies of up to 2.5¿eV. Further downstream, the profile collapses radially and contracts. A much higher electron density is found (2 × 1019¿m-3) while the mean energy is lower (0.5¿eV).