Tabletop laser creates dense beams of ultrarelativistic positrons

New Scientist : In 2008, researchers created positrons by using a powerful laser to accelerate electrons toward a metal target, thereby circumventing the need to use a particle accelerator. A new process makes the creation of antimatter an even simpler and cheaper proposition. Gianluca Sarri of Queen’s University Belfast, UK, and his colleagues fired pulses of laser light at helium gas and created a stream of high-energy electrons. The stream was focused at a thin foil where the electrons collided with the metal atoms, releasing both electrons and positrons (antimatter electrons) that were separated into two beams by magnets. The positron beams lasted just 30 fs, but each beam contained 10¹⁵ positrons per cm³. That density is comparable to the positron production at CERN, which uses a 190-m-long accelerator track. Sarri and his group hope to use the high-energy, narrow beams of antimatter they are creating to model the particle fountains associated with black holes and pulsars.