No abstract

The dynamic spectral observation at decametric wavelength is important to study solar radio physics and space weather. However, the observing system is difficult to observe with high sensitivity at this band due to the fact that the system temperature is dominated by the sky background noise and the antenna is difficult to design with high gain. An effective solution to improve the sensitivity is constructing an antenna array based on the beamforming method. Accordingly, we develop a decametric solar radio spectrometer system based on 4-element beamforming array. The system consists of 4 antennas, an 8-channel analog receiver and digital receiver.We use the true time delay to implement the beamformer and the classical FFT method to perform spectrum analysis in the digital receiver. Operating at a frequency range of 25 - 65 MHz with dual-circular polarizations, the system provides high resolution dynamic spectrum with spectral resolution of ∼ 12 kHz and temporal resolution of ∼ 5.3ms (typical). Many solar radio bursts have been observed successfully during the period of the trial observation, demonstrating the system’s ability to detect fine structures with high spectral and temporal resolution. In this article, we present the design, implementation, and initial observation results of the decametric solar radio spectrometer system in detail.

High-emissivity coatings are commonly applied in satellite detectors and large-scale cryogenic systems. Accurate and quick measurement of emissivity is in high demand for practical applications at cryogenic temperatures. In this paper, a method for the measurement of the total hemispherical emissivity from 50 K to 300 K was presented based on the static calorimetric method. A two-stage GM cryocooler was used as a cooling source in the measuring device without assumption of cryogenic liquids. The thermal emissivity of a black carbon coating was measured by monitoring temperatures timely in the device. The tested results exhibited good accordance with previous reports. This cryogenic measurement device has made it a strong candidate for the radiative heat dissipation at cryogenic temperatures. Design details of the experiment and measurement results will be presented.