The Linear Accelerator

Electrons emitted from a heated filament are accelerated in a special 30 meter long vacuum pipe under the action of a microwave electric field. Positrons, the positively charged antiparticles of the electron, do not normally occur in matter but are produced by accelerating electrons up to 140 MeV at an intermediate point of the linac where they strike a tungsten plate. A spray of electrons, positrons and X-rays emerges from the plate. The positrons are selected, focused, accelerated in the remaining length of the linac up to the 200 MeV final energy, and injected into the synchrotron.

MPEG clips:

• Prebuncher (1300 kbyte MPEG) shows the beam as it comes out of the electron gun and is compressed in the prebuncher.
• Converter (4300 kbyte MPEG) shows the electron beam striking a heavy metal target, and the collection and acceleration of the resulting positrons.
• RF Accelerator Cutaway (2500 kbyte MPEG) shows a cut away of one of the eight Acceleration Cavities in the Linear Accelerator, where the oscillation of the powerful electric field from a radio wave accelerates the electron or positron beam.