discovered_01_2016 - Plasma Flash in the Supercomputer

WWW.HZDR.DE 10 11 TITLE // THE HZDR RESEARCH MAGAZINE Laser particle acceleration is a highly-complex process: An ultra-short light pulse hits matter and produces a plasma, which catapults electrons to nearly the speed of light in subseconds and accelerates ions. In order to harness this process for applications in fields like tumor therapy, experimental physicists want to make it as effective as possible. They are being supported in their efforts by their theoretical colleagues: With the help of the world’s best supercomputers, HZDR physicist Thomas Kluge simulates laser-acceleration and acquires profound insights into the physical events. His findings help to elucidate the experiments and optimize them for future measurements. "Just imagine bundling all the solar radiation that hits the earth on the tip of a pencil," Thomas Kluge explains. "That’s the power of each of our laser pulses – although it only lasts for 30 femtoseconds, that is, for 30 quadrillionths of a second." What happens when these ultra-intense light pulses encounter a solid, such as a thin metal foil? "It’s tricky to simulate on a computer," the theoretician answers, "because during the processes a number of extreme events happen all at once." What this means in practice is that when the light pulse hits the foil, it produces such a high electromagnetic field that the atoms it is composed of are immediately ionized: Within femtoseconds, electrons are swept out of the atomic shell, leaving behind positively-charged ions. A strong electric field is generated that catapults out some of the ions with huge momentum – a highly-effective method of acceleration. But there is a hitch: During these processes, instabilities occur. For example, the electrons do not usually exit the foil in one homogeneous beam, but in lots of little beams. This, in turn, influences the accelerating field that the ions "see" in the foil. Instead of an even surface, it is deformed to a greater or lesser extent. // How HZDR theoretician Thomas Kluge uses computers to simulate laser acceleration. _TEXT . Frank Grotelüschen PLASMA FLASH IN THE SUPERCOMPUTER INSIGHT: Physicist Thomas Kluge uses super computers to simulate particle acceleration with high-power lasers. Photo: Oliver Killig

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