When a suitable accelerating voltage is applied to extract negative ions from a volume production source, electrons are also extracted. If no means of suppression is utilized, the electron current in a hydrogen plasma would typically be of the order of 80-100 times the negative-ion current. In the accelerator designs in use at Culham Laboratory, electrons entering the accelerator are dumped in a trap within the second electrode at a small fraction of the beam energy. Even using this technique, a considerable amount of power would be expended unnecessarily in accelerating electrons to the trap. The suppression of electrons at the source/accelerator interface can be achieved by means of a magnetic field applied across the extraction aperture. This traps electrons, which are then collected on an electrically biased subsection of the first electrode. Experiments performed with an electromagnet configuration have shown that the electron flux entering the accelerator can be reduced as approximately the reciprocal of the square of the magnetic field strength.