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discovered 02_2012

FOCUS// The HZDR Research Magazine WWW.Hzdr.DE 24 25 // High-performance lasers are excellent for accelerating particles. The more power you pack into an ultra-short laser pulse, the more energy the particles gain from the acceleration. Physicists at HZDR have come up with a new equation to describe the temperature and density of laser-driven electrons. If it is correct, then it will take higher intensity lasers than previously thought to produce the ion beams needed for applications such as cancer therapy. _TEXT . Michael Bussmann & Christine Bohnet Translation . Peter Gregg Shedding new light on laser heating – electrons heated to several billion degrees We all take it for granted that water boils at 100 degrees Celsius, say, while making our morning cup of tea or coffee. But imagine if, one day, we suddenly had to heat the water to 200 degrees Celsius to get it to boil. We would have to double the power of our kettles and espresso machines to brew our beloved beverage in the usual time. Then, the power plants would have to put out twice the power so that we can all start our mornings in customary fashion. Sounds kind of strange, right? But that is pretty much exactly the situation doctoral student Thomas Kluge and colleagues at HZDR have encountered, although his kettle is a high-power laser and the water is electrons on the surface of a foil. In short, it takes a much more powerful laser pulse than expected to heat electrons to a certain temperature in a foil. A high-power laser accelerates electrons and ions in the following process: First, an intense, ultra-short laser pulse strikes the front side of a thin foil, where it produces a plasma of ions (atoms that have lost some or all of their electrons) and hot electrons. The electrons are heated by the strong fields of the laser, similar to how water is heated in a kettle. The electrons then shoot out of the foil on the reverse side, pulling the ions along behind them, accelerating them to high energies. The scientists harvest these fast-moving ions for use in their research and, one day, in applications such as radiotherapy. SUPERCOMPUTER: To produce high parallel simulations, the “Computational Radiation Physics” junior research group headed by Michael Bussmann employs innovative programming techniques using state-of-the-art high-performance computers, as well as experiments with new kinds of analytic techniques.