[en] Attention is directed towards instabilities induced in hydrogen plasmas due to the presence of the desired H/sup /minus// ions. Preliminary investigations indicate that when the electron temperature exceeds the temperature of the background ions (H⁺), the H/sup /minus// beam causes collective instabilities even at very low (even vanishing) beam velocities, provided that the non-ideal properties of the background plasma are taken into consideration. The most dangerous instabilities involve oscillations transverse to the direction of beam extraction, and may thereby degrade the beam emittance. 5 refs