Why electrons?

Electrons are relatively easy to accelerate due to their high electric charge and their small mass. The best know example of an electron accelerator is the television. Within the tube of such a device a metal rod is heated which causes electrons to be ejected out of the rod. These electrons are then accelerated by means of an electric potential (voltage). As such a simple 1.5 Volt battery is sufficient to accelerate the electrons up to a speed of 700 km/s. A normal color-TV employs 20,000 Volt, which is sufficient to accelerate the electrons to almost 90,000 km/s. At BESSY II we use 1,700,000,000 Volt which accelerates the electrons to a velocity of almost 300,000 km/s, i.e. the velocity of light.