High-speed VUV spectroscopy for edge impurity line emission measurements in HL-2A tokamak

A 20 cm focal length normal incidence vacuum ultraviolet （VUV_20 cm） monochromator with a fast time response has been developed for measuring edge impurity line emission in the wavelength range of 300-2000 A on an HL-2A tokamak. An aberration corrected concave holographic grating with 1200 grooves/mm is adopted in the monochromator, which provides a wavelength dispersion of 40 A mm-1. The aperture is f/4.5. A channel electron multiplier is used as a detector. The time resolution of the system is 17 μs. Wavelength calibration of the system has been done by using a hollow cathode light source in the laboratory with helium and argon gases. The obtained signals of helium and argon spectra are very strong since the inner surface of the monochromator vacuum chamber is blackened and the stray light level is then significantly reduced. The optical property of the system has been examined by scanning the width of the entrance and exit slits. The system is then installed at the mid-port of the HL-2A tokamak and typical line emissions from the HL-2A plasma are measured. Time behaviors of edge impurity line emissions are observed with the fast time response system in different plasma confinement regimes, especially in the H-mode discharges. The result shows that the VUV_20 cm system works very well to measure the edge impurity line emissions in the edge localized modes phase of H-mode discharges.

Foraging Responses of the Larvae of Invasive Bullfrogs (Lithobates catesbeianus)： Possible Implications for Bullfrog Control and Ecological Impact in China

The predatory behavior of invasive species can affect their ecological impact, and offer opportunities for targeted control. In Australia, tadpoles of invasive cane toads （Rhinella marina） do not consume eggs of native anurans, but are strongly attracted to （and consume） newly-laid eggs of conspecifics; chemical cues from such eggs （or adult secretions） thus can be used to attract toad tadpoles to traps. Do other invasive anurans show similar selectivity？ Our laboratory trials on a Chinese population of invasive American bullfrogs （Lithobates catesbeianus） revealed similar behaviors as exhibited by Australian cane toads. Bullfrog tadpoles rarely consumed the eggs of native anurarts, but were attracted to both bullfrog eggs and bullfrog skin secretions. Although the attraction response was less intense in bullfrogs than in cane toads, it might nonetheless enable selective removal of bullfrog tadpoles from invaded sites.

Scattering by Large Bubbles: Correction for Debye Coefficient at a Small Number of Sub-Waves

I found that when the Debye theory calculates the far-field scattered light intensity of bubbles, the forward scattered light intensity is quite different from the result calculated by the Mie theory due to the convergence problem, so the expression of the Debye coefficient has been revised. I derived the Debye reflectance and transmittance according to the physical meaning of Debye theory and compared them with Fresnel’s formula. I modified the Debye coefficient expressions for bubbles based on the differences between the Debye reflectance and transmittance from the Fresnel formula. Finally, compared with the far-field scattered light intensity calculated by the original Debye theory, the far-field scattered light intensity calculated based on the modified Debye coefficient can obtain more accurate forward scattered light intensity with fewer sub-waves.