For the first time, researchers have used an X-ray laser to measure how a laser blast-generated plasma expands in the hundreds of femtoseconds after its creation. The findings are expected to advance understanding of plasma instabilities and lead to the next generation of laser-based ion accelerators with applications in medicine, plasma physics and astrophysics.
The experiments conducted at the U.S. Department of Energy’s SLAC National Accelerator Laboratory are part of an effort to harness the behavior of plasma to create a new type of particle accelerator for proton therapy, an existing cancer treatment that involves blasting tumors with charged particles rather than X-rays.
At LCLS, researchers zapped solid samples with a laser to create plasma, then used an X-ray scattering technique to watch it expand and collide. Source:Matt Beardsley/SLAC National Accelerator LaboratoryThe researchers hope to harness the proton streams emitted when a solid is subjected to a laser, resulting in plasma formation, to treat tumors and destroy cancer cells. Producing these protons in a reliable way requires a better understanding of how plasma changes as it expands. A high-power, short-pulse optical laser beam was used at SLAC to create the plasma and the Linac Coherent Light Source (LCLS) X-ray free-electron laser to probe it.
Simulations show that the researchers achieved a new temperature record for matter studied with a free-electron laser: 36 million° F, almost 10 million degrees hotter than the sun’s core. Solid samples consisting of raised silicon bars were fabricated and exposed to intense, short pulses from the optical laser. Tiny amounts of plasma were observed to accumulate between the raised bars in the quadrillionths of seconds following laser pulses. A special form of scattering that uses X-ray pulses from LCLS allowed the team to peer inside the plasma to follow its evolution.
This technique will enhance the understanding of plasma instabilities and allow engineers to create proton sources for cancer therapy with relatively small footprints that, unlike conventional accelerators, can be operated within a hospital. It will also be useful in research relevant to fusion energy, other types of novel particle accelerators and laboratory astrophysics.
Scientists from Helmholtz-Zentrum Dresden-Rossendorf, Technical University Dresden, European XFEL, SLAC, Universität Siegen, Freidrich-Schiller-Universität, Leibniz Institute of Photonic Technology and Osaka University participated in this research, which is published in Physical Review.
