He neutral beams of 29.5 keV/amu have been injected into He plasmas on the JET tokamak. Thermal neutral He in its ground state forms along the beam trajectory due to resonant double charge exchange. This is the first observation of He-He double charge exchange in a laboratory plasma. The cross section is measured as (2.05±0.49)x10-16cm2, about twice the value predicted by theoretical models and measured in ion beam into gas experiments. The signal from the halo is used to measure the plasma ion temperature and the frequency of toroidal rotation and can be used to infer the He ion density.