Energetic neutral particles from neutral hydrogenic beam heating systems are widely used for active spectroscopic measurements of key plasma parameters in fusion experiments. Helium beams are used in dedicated diagnostic beamlines offering deeper penetration and resonant double charge exchange with alpha particles. Neutral beam systems using pure helium either require specialised helium gas pumping with a pumping speed in excess of 1000 m3/h or are restricted to short pulses (normally less than 1 s). A doped hydrogen/helium beam combines the requirements for plasma heating and diagnostics without the need for sophisticated helium pumping. A small flow of helium gas is injected into the plasma source for the time helium particles are required. The helium current is typically 10% of the total extracted current. The reduction in heating power of the doped beam can be kept below 5%. Doped deuterium/helium beams have been successfully tested and routinely used at JET. HeI beam emission spectra obtained with a doped deuterium/helium beam offer sufficiently strong visible lines for spectroscopic applications.