Compelling Plasma Pair Production

Annihilation and pair production are two of the most fundamental processes in quantum physics and are the most basic application of Einstein’s mass energy equivalence principle. The Breit-Wheeler process is the most common mechanism for how pair production is induced involving two photons colliding to produce an electron and positron pair. Despite being suggested in 1934 by Gregory Breit and John Wheeler it was only tow years ago, in 2014, that it first became observed in a laboratory. This is because forcing two gamma ray beams to collide is incredibly difficult. But eighty years after the theory was proposed, physicists at Imperial College realised that by using a laser they could accelerate electrons to relativistic speeds and slam them into a dense material like gold. This then produces a photon beam many orders of magnitude more energetic then normal light. By firing a second laser into a metal box line with more gold a very dense thermal radiation field (the inside of the box constantly radiating). Directing the produced photons into the gold box causes collisions which were observed to produce the expected electrons and positrons. Another method is being developed in order to try and make the production of positrons more efficient so they may be used to study astrophysical effects. This new method involves firing two lasers in exactly opposite directions into an already energised plasma. The laser radiation can get trapped between the plasmas electrons as they constantly emit and absorb it. As this is happening from both directions due to the counterpropagating waves the gamma rays are much more likely to collide and induce the Breit-Wheeler process. The energy efficiency has been shown to be about 0.14% which, for high energy systems like this, is really not that bad.  This method is currently showing some promise and could very well be the mechanism used in the future to produce pairs of high energy particles.


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