discovered_01_2016

WWW.HZDR.DE discovered 01.16 TITLE PENELOPE: HZDR researchers want to use this new laser to accelerate protons to energies that can be used for cancer therapy. It will take several months before the first experiments can be undertaken. Photo: Oliver Killig Hope for the superlaser In order to capture the protons and bundle them into particle pulses, researchers have installed a special magnet at the back of the foil – a magnetic coil with powerful windings through which strong electrical pulses can be unleashed. A magnetic field up to 30 Tesla captures the proton pulses and focuses them in the right direction. Detectors subsequently measure the pulses. In this way, experts can determine how successful an experiment has been. "We can already demonstrate that the principle works," says Zeil. "We have accelerated protons up to 20 MeV on a distance of no more than just a few micrometers." For use in hospitals, however, ten times the amount of particle energy is required, and in order to achieve this, researchers are trying to improve the method in a number of different ways. It is as yet unclear, for example, what are the most appropriate kinds of targets. Among others, the Dresden researchers are experimenting with plastic-coated metal foils as well as refrigerated "wires" of frozen hydrogen. But at the heart of the strategy are even stronger laser pulses, which should mean the ions can be accelerated to significantly higher energies. The course has already been set. Karl Zeil enters a room that is nearly twice as large as the DRACO laser lab. It is still fairly empty, but the first components have already been installed. "This is where PENELOPE is being constructed, our new high-power laser," Zeil explains. "It is based on high-power diode laser technology and will generate significantly longer light pulses than DRACO for the same output – 150 femtoseconds instead of 30." These longer pulses should prove particularly suited to accelerating ions – at least that is what the computer simulations predict. "We want to reach proton energies with PENELOPE which will be relevant for therapies," says Zeil. "In two or three years, we hope to know whether the method will achieve what we want and whether it’s worth building a clinical prototype." They already have a concrete plan: The prototype is supposed to be constructed in the OncoRay Center, a facility run jointly by HZDR, the University Hospital und TU Dresden. In a combined radiation room, the new technology could be directly compared with the old – laser pulses versus radio waves. And the high-power lasers, which currently take up huge spaces, could basically be made much more compact. "This development has only been underway for a short while," Zeil comments. "The potential is enormous." PUBLICATIONS: K. Zeil et al.: "Direct observation of prompt pre-thermal laser ion sheath acceleration", in Nature Communications 2012 (DOI: 10.1038/ncomms1883) K. Zeil et al.: "Dose-controlled irradiation of cancer cells with laser- accelerated proton pulses", in Applied Physics B – Lasers and Optics 2012 (DOI 10.1007/s00340-012-5275-3) A. Jochmann, A. Irman et al.: "High resolution energy-angle correlation measurement of hard X-rays from laser- Thomson backscattering", in Physical Review Letters 2013 (DOI: 10.1103/ PhysRevLett.111.114803) CONTACT _Junior Research Group on Laser-electron Acceleration at HZDR Dr. Arie Irman a.irman@hzdr.de _Junior Research Group on Laser-ion Acceleration at HZDR Dr. Karl Zeil k.zeil@hzdr.de

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