An extraordinary-mode (X-mode) frequency-modulated continuous-wave (FMCW) profile reflectometer has been built on EAST. In the reflectometer, continuous waves with frequency sweeping from 12.5 GHz to 18 GHz were generated through a Hyperabrupt Tuned-varactor Oscillator (HTO) source and a four times active multiplier was used to increase the frequency to V-band (50 GHz to 72 GHz). The polarization of horn lens antenna is perpendicular to the magnetic field line at the edge plasmas. According to the V-band frequency range and polarization, the system cover density range from 0.5 × 10 19 m −3 to 3.0 × 10 19 m −3 (when toroidal magnetic field is 1.8 T), with time resolution of 12.5 ∼ 50 µs. The density profile could be calculated by assuming the edge profile through an empirical equation. The maximum spatial error deduced by the method is about 4 cm. This reflectometer has been successfully applied in 2010 autumn EAST campaign, the temporal evolution of density profiles was acquired during the low confinement mode to high confinement mode transition. The density pedestal of EAST Tokamak was observed and the top value and gradient of the density pedestal were estimated.
Compact torus (CT) injection is one of the most promising methods for the central fuelling of next-generation reactor-grade fusion devices due to its high density, high velocity, and self-contained magnetised structure. A newly compact torus injector (CTI) device in Keda Torus eXperiment (KTX), named KTX-CTI, was successfully developed and tested at the University of Science and Technology in China. In this study, first, we briefly introduce the basic principles and structure of KTX-CTI, and then, present an accurate circuit model that relies on nonlinear regression analysis (NRA) for studying the current waveform of the formation region. The current waveform, displacement, and velocity of CT plasma in the acceleration region are calculated using this NRA-based one-dimensional point model. The agreement between the model results and the experimental results is better than in the previous general model results estimated by the device dimensions in previous. The next-step upgrading reference scheme of the KTX-CTI device is preliminarily investigated using this NRA-based point model. This research can provide insights for the development of experiments and future upgrades of the device.
With the rapid development of urban rail transit and underground space development, the occurrence of excavation near existing tunnels is becoming more common. This excavation and unloading will inevitably cause soil deformation outside the pit and the tunnel buried therein. This paper presents an investigation into the entire excavation process and the deformation effects on the adjacent subway structure under complex construction environments, including soft soil foundations and adjacent subway intersections, based on measured data of pit construction. The horizontal and vertical displacements of deep soils in two pits were analyzed along with safety management measures to determine the horizontal displacement curve pattern and the lateral displacement development distribution law of deep soils. The analysis of subway deformation data shows that after excavation, the subway tunnel undergoes “lateral expansion” and “vertical compression” type deformation, accompanied by “in-pit” horizontal displacement and “settlement” vertical displacement. Furthermore, a correlation analysis reveals a clear linear relationship between pit deformation and subway structure deformation, which can be used as a prediction method for adjacent structure deformation. Finally, a comparative analysis of existing relevant influence zone models and tunnel deformation prediction formulas is carried out based on the monitoring. The results of this study have significant guiding implications for the excavation construction of soft soil foundations in the vicinity of subway crossings.
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