The in situ diagnostic of the composition and content of the first wall materials in tokamak devices is an important research interest of the plasma-wall interaction. Laser-induced breakdown spectroscopy (LIBS) has become an attractive tool for in situ diagnostic of the first wall materials. It has the ability to analyze the composition of the first wall remotely and on-line without sample manipulation or pretreatment. In tokamak, using the LIBS method in a fixed window to diagnose wall materials in different positions will inevitably affect the LIBS measurement signal due to different laser ablation and light collection angles. In this paper, we got the determination of the relationship between the intensity of the tungsten spectral line and laser energy in the laboratory as a prerequisite. And the effects of different ablation angles on the temporal evolution of the spectrum of the laser ablated tungsten material were investigated in detail. This provides a reference for in situ LIBS analysis. RECEIVED
In this paper, we have investigated the spatial confinement effects on the spectrum intensity of tungsten plasma generated by laser-induced breakdown spectroscopy in the near-vacuum environment. The enhancement effects that vary with the diameters of the spatial confinement cylinders and with the material type are analyzed. We find that for an Al cylinder, the enhancement factor o reaches its highest value at diameter 4mm. The primary causes behind this finding are attributed to the influences of diameter on the bounce time of shock wave propagating in the plasma as well as on the available range of spectrum collection. Moreover, the enhancement effect of Al cylinder is better than the other four types of materials: ZrO2, Al2O3, Fe and Cu. For each of the latter four types of materials, the thermal conductivity plays a major role on the enhancement effect, whereas for Al the enhancement effect is mainly due to its extremely large reflectivity. Particularly, for cavity with a diameter of 4 mm made of Aluminum, the maximum of the enhancement factor can approximately reach as high as 15. These experimental results indicate that the signal intensity of laser-induced breakdown spectroscopy can be dramatically improved by appropriately selecting diameter and material type of the cylindrical cavity.
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