You may be looking for:
Ion cannons are a protoss technology developed for the phoenix and later the mirage. They fire beams of negatively charged ions, doing heavy damage to armored targets. The short wavelength of the ions allow the cannons to be fired on the move, but at a short range. The ion cannons’ effective combat range presented a problem until the protoss began to replace the old focusing lenses with the more advanced anion pulse-crystals.