471 / 2019-03-16 22:07:35

Spectroscopic diagnostic of isolated dense plasma generated through laser driven gold hohlraum radiation

Laser-produced plasma; Stark broadening; Plasma diagnostics; Electron temperature; Electron density

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Dense plasma attracted a lot of attentions these years since it widely exists in the super- nova, stellar interior, accration disks, and is the important state of matter in inertial confinement fusion. The routine way to generate dense plasma in laboratory is to heat solid samples with laser. In laser-solid interaction, the laser cannot penetrate into solid, but is reflected on the critical surface. The target bulk are heated and ionized through the propagation of these energetic electrons. In this way, the temperature as well as the free electron density shows great gradient, and the hydrodynamic behavior of the target cannot be neglected. This invokes great challenge for the fast diagnostics techniques and detailed understanding of target evolution. In order to generate uniform, longliving dense plasma in laboratory, we used TAC foam (C12H16O8) as the sample material, which was heated by hohlraum radiation. With this method, the hydrodynamic effects of the target could be neglected in timescale of 10 ns.
The measurement was carried out at the XGIII facility. Combined target consisting of a gold hohlraum converter and a 2 mg/cm−3 TAC foam layer was used. Within this scheme, the ns laser (2ω) with energy of 150 J inter- acts with the inner gold wall of the cylindrical hohlraum, which will induce blackbody-like radiation. The emitted X rays then volumetrically heat the foam to plasma state. The emission spectra of both gold hohlraum and CHO plasma were measured. Pinhole cameras which is sensitive to X rays are used to image the plasmas. XRDs were used for the time-resolved measurement of Xray flux. Transmission Grating Spectrometer and Flat field Grating Spectrometer are used for the measurement of X ray emission with spectral resolution.
Fig.1 shows the emission lines of the CHO plasma in range of 10-28 nm. Through analysing the broadening and intensity of helium-like carbon lines with Saha-Boltzmann curve slope method and Stark line broadening method, it was obtained the electron temperature is around 19eVandthe free electron densityisabout1.0×10 21cm−3.

Figure 1. Self-emission spectra of the CHO plasma
Keywords: Laser-produced plasma; Stark broadening; Plasma diagnostics; Electron temperature; Electron density