Radiative characterization of supersonic jets and shocks in a laser-plasma experiment

Abstract

The interaction of supersonic laser-generated plasma jets with a secondary gas target was studied experimentally. The plasma parameters of the jet, and the resulting shock, were characterized using a combination of multi-frame interferometry/shadowgraphy, and x-ray diagnostics, allowing for a detailed study of their structure and evolution. The velocity was obtained with an x-ray streak camera, and filtered x-ray pinhole imaging was used to infer the electron temperature of the jet and shock. The topology of the ambient plasma density was found to have a significant effect on the jet and shock formation, as well as on their radiation characteristics. The experimental results were compared with radiation hydrodynamic simulations, thereby providing further insights into the underlying physical processes of the jet and shock formation and evolution.

Laser-generated supersonic plasma jets and shocks in a transverse magnetic field

“…The stagnant (backing) pressure in the reservoir of the nozzle was varied in the range of p = 10 − 40 bar. The argon neutral density profile, measured with interferometry using a continuous-wave (CW) Helium-Neon (He-Ne) laser, is shown in figure 1(b) for a backing pressure of p Ar = 40 bar [26]. The geometry of the laser-target setup is also shown, with the blue dashed lines indicating the edges of the laser light cone.…”

“…The latter could also be used to determine the velocity of the plasma expansion by tracking the location of the jet and shock features between frames. An x-ray streak camera mounted from the top was used to provide a cross-check of the copper jet velocity for the unmagnetized case as described in Bohlin et al [26].…”

“…The interaction characteristics and typical parameters of the jets and shocks without the magnetic field are outlined in greater detail in Bohlin et al [26]. Due to the limitation of the diagnostic access with the coil installed, the electron temperature measurements using filtered x-ray pinhole camera imaging described therein could not be implemented.…”

“…The resulting collimated outflows have a radius around r J ∼ 150 µm, and are observed to extend several millimeters from the target before the density drops below the detection limit of the diagnostics. The jets have an electron density on the order of n e ∼ 10 19 cm −3 , and an electron temperature in the range of T e = 50-150 eV [26]. The velocity of the jets can be varied through the laser energy, and is typically in the range of v J ∼ 400-700 km s −1 , which allows for the impact of the ram pressure on the interaction with the magnetic field to be investigated.…”

“…The radiative properties of the jets and shocks were studied further by Bohlin et al [26], with key results including measurements of the electron temperature of the jet and shock using filtered x-ray pinhole camera imaging, and identifying the copper plasma as the main source of the observed x-ray emission. It was also shown that the shock structures are highly dependent on the topology and density of the background plasma by its influence on the initial jet formation and geometry.…”