Laser-plasma experiments reveal new magnetic wave patterns that could transform fusion research
Scientists have identified two types of magnetic waves that spontaneously form when ultraintense lasers ablate targets, creating expanding plasma clouds. The discovery matters because these waves are strong enough to detect in real experiments and could help researchers better control and harness laser-plasma interactions for fusion energy and other applications.
Originaltitel: Weibel- and non-resonant Whistler wave growth in an expanding plasma in a 1D simulation geometry
<p>Ablating a target with an ultraintense laser pulse can create a cloud of collisionless plasma. A density ramp forms, in which the plasma density decreases and the ion's mean speed increases with distance from the plasma source. Its width increases with time. Electrons lose energy in the ion's expansion direction, which gives them a temperature anisotropy. We study with one-dimensional particle-in-cell simulations the expansion of a dense plasma into a dilute one, yielding a density ramp similar to that in laser-plasma experiments and a thermal-anisotropy-driven instability. Non-propagating Weibel-type wave modes grow in the simulation with no initial magnetic field. Their magnetic field diffuses across the shock and expands upstream. Circularly polarized propagating Whistler waves grow in a second simulation, in which a magnetic field is aligned with the ion expansion direction. Both wave modes are driven by non-resonant instabilities, they have similar exponential growth rates, and they can leave the density ramp and expand into the dilute plasma. Their large magnetic amplitude should make them detectable in experimental settings.</p>