Previous experiments found it difficult to measure plasma spectra because the high temperatures inside the plasma caused the spectral lines to blur. The Weizmann team solved the problem by adding oxygen ions to the plasma: these ions are less disturbed by the heat and density inside the plasma and produce clear spectral lines. Maron's team were able to measure the oxygen spectral lines, and hence the current in the plasma, every billionth of a second. They found that when the current first hit the "roll" of plasma, it flowed on the outside of their sample. By measuring how far the current penetrated the plasma, they were able to determine the velocities of the particles inside the plasma. Under the influence of the applied magnetic field, some particles reached velocities of 100 kilometres per second. Closer studies of current, and hence magnetic fields, in plasmas can allow scientists to improve plasma compression and help generate fusion.