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newscientist 00514.txt

#Tabletop accelerator shoots cheap antimatter bullets Make way for the antimatter gun. A tabletop device just 10 square metres in size can spit out energetic bursts of positrons as dense as those kicked out by the giant particle-factories at CERN. Each positron-packed bullet lasts for just a fraction of a second so don't expect to fill the tank of your antimatter engine any time soon. Instead the smaller cheaper machine might help labs around the world study deep-space objects such as powerful radiation jets squirted out by black holes. Antiparticles have the same mass as their ordinary particle counterparts but carry an opposite charge and spin. The particles annihilate on contact with ordinary matter vanishing in a puff of energy which makes it difficult to produce and study them On earth. Huge machines at particle physics labs such as CERN near Geneva Switzerland have been churning out antimatter for over a decade. But it is an expensive pursuit that for CERN requires a 190-metre-long track. Instead Gianluca Sarri at Queen's university Belfast UK and colleagues used rapid laser bursts to make positrons in their smaller budget device. The laser pulse ionises inert helium gas generating a stream of high-speed electrons. This electron beam is directed at a thin metallic foil so that it crashes into metal atoms releasing a jet of electrons and positrons. These particles are separated into two beams with magnets (Physical Review Letters doi. org/m2n. The team call their device an antimatter gun because the bursts of positrons last just 30 femtoseconds (quadrillionths of a second). Despite their short duration the beams contain a quadrillion positrons per cubic centimetre says Sarri meaning they are comparable in density to the ones made at CERN. In 2008 scientists at the Lawrence Livermore National Laboratory in California produced large quantities of antimatter by directing an extremely powerful laser at a tiny gold disc. Sarri says his setup is much more practical and cheaper: They needed much stronger lasers and those lasers are expensive. Also they produced streams of positrons that were extremely broad whereas our jet is a hundred times narrower and remains pencil-like as it propagates he adds. This is similar to the powerful streams of matter-antimatter observed outside pulsars and black holes. CERN physicist Niels Madsen notes though that the tabletop device has limitations. It only makes relatively light particles like positrons whereas to make an anti-atom you also need antiprotons which are almost 2000 times more massive. For now he says making heavier antiparticles is not doable in a small lab in a cheap fashion. Nor does the smaller machine address the problem of antimatter storage. To hold antimatter stable it must be chilled and the tabletop method makes searing-hot beams of particles moving at near light speed. As an alternative says Sarri the beams can be used to mimic the way particle fountains from black holes and pulsars shoot through and interact with gases in the interstellar medium creating mini versions of these enigmatic astrophysical phenomena in the lab for the first time. This article will appear in print under the headline Antimatter bullets get fast and chea a

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