Pan Yuan

Electromagnetic Wave Attenuation in Atmospheric Pressure Plasmas

The properties of electromagnetic waves in atmospheric pressure plasmas are investigated with the Lorentz model. The effects of the electromagnetic wave frequency, plasma density, and the electron-neutral collision frequency on the attenuation of electromagnetic waves are discussed. The numerical results indicate that the wave attenuation is stronger at the region of the longer wavelength and at the higher plasma density.

Reconstruction of the TEXT-U Tokamak in China

The joint TEXT (J-TEXT) tokamak, formerly TEXT/TEXT-U tokamak, operated by the University of Texas at Austin in USA, has been re-built up in Huazhong University of Science and Technology in China. The machine has been run for two experimental campaigns since 2007. Discharges with plasma current beyond 200 kA and duration of 300 ms have been obtained. At present all sub-systems, such as poloidal field (PF) and toroidal field (TF) power supplies, vacuum system, diagnostics systems etc, are successfully integrated into the routine operation. The plasma position can be elaborately controlled within two centimeters. The operational scenario of J-TEXT are typical of the machine and easily understandable compared to the former TEXT/TEXT-U results.

Early Stage of Pulsed Discharge in Water

The bubble radius at the early stage of discharge in water is investigated using high-speed photography. Some simulation results on the bubble radius are presented, which are in agreement with the experimental results, with a maximum difference of about 10%. The reasons why the peak pressure of the first shock wave is only related to the energy released in the bubble during the first half period are addressed. The energy released in the bubble after the first half period increases the bubble pulsation period, but it produces no more than 10% under the peak pressure of the second shock wave.

The Power Supply System for the J-TEXT Poloidal Field

Joint-TEXT (J-TEXT) is a medium-sized tokamak constructed at Huazhong University of Science and Technology. At present, the poloidal field power supply consists of three subsystem sets, namely Ohmic heating field power supply, vertical field power supply, and horizontal field power supply. The structure and function of the poloidal field (PF) power supply as well as the updated control system of the power supply is described. The new scheme uses the realtime feedback control method for the poloidal field power supply. The experimental results show that the poloidal field energized by poloidal field power supply meets the J-TEXT operational requirement perfectly.

Propagation of Electromagnetic TM (S-Polarization) Mode in Two-Dimensional Atmospheric Plasma

The finite-difference-time-domain (FDTD) method is applied to simulate the two-dimensional propagation of electromagnetic TM (S-polarization) mode in atmospheric plasma and in metal layer for strong electron-neutral collisions. Dependence of the wave attenuation on both plasma parameters and incident wave angle are obtained. It is indicated that for a given electron density profile the attenuation depends strongly on the incident angle, the wave frequency, the width of plasma layer, and the collision frequency between electrons and neutrals.

A Visible Light Imaging System for the Estimation of Plasma Vertical Displacement in J-TEXT

A wide-viewing-angle visible light imaging system (VLIS) was mounted on the Joint Texas Experimental Tokamak (J-TEXT) to monitor the discharge process. It is proposed that by using the film data recorded the plasma vertical displacement can be estimated. In this paper installation and operation of the VLIS are presented in detailed. The estimated result is further compared with that measured by using an array of magnetic pickup coils. Their consistency verifies that the estimation of the plasma vertical displacement in J-TEXT by using the imaging data is promising.

Finite-Difference Time-Domain Analysis of Wave Propagation in a Thin Plasma Layer

The propagation property of an electromagnetic wave in a thin plasma layer at high pressure is investigated with the finite-difference time-domain method. The effects of the non-uniformity of plasma distribution, and the frequency of incident wave on the propagation property of the electromagnetic wave are discussed. Numerical results indicate that the phase shift and the reflectivity of wave are sensitive to plasma density distribution, and reflectivity is lower at the middle band of frequency for different plasma distributions.

Effects of ambient pressure on bubble characteristics

The effects of the ambient pressure Pambient on the bubble characteristics of pulsed discharge in water are investigated. The simulation results show that, when Pambient increases from 1 atm to 100 atm, the bubble radius R decreases from 4 cm to 7 mm, and its pulsation period decreases from 8 ms to 0.2 ms. The results also show that the peak pressure of the first shock wave is independent of Pambient, but the peak pressure of the second shock wave caused by the bubble re-expansion decreases when Pambient increases. On the other hand, the larger the ambient pressure, the larger the peak pressure of the plasma in the bubble, while the plasma temperature is independent of Pambient.

Design of the Control System of Toroidal Field (TF) Power Supply for J-TEXT Tokamak

J-TEXT, formerly TEXT-U at the University of Texas at Austin in USA, is a medium-sized tokamak at the Huazhong University of Science and Technology. The toroidal field (TF) power supply of this tokamak should provide a current of 160 kA and a flat duration of 500 ms for the toroidal field coils to generate a maximum toroidal field of 3 T at the geometric center of the vaccum vessel. This paper presents a design of a new control system which takes the real-time feedback control option for the TF power supply operation. The system was tested successfully during the commissioning. In the first experimental campaign of J-TEXT, the system effectively controlled the power supply to provide a flat current up to 92.5 kA and therein the TF produced reached 1.74 T, which enabled the machine to generate the first plasma successfully.

Calculation of Magnetic Field in J-TEXT with an Unsaturated Iron Core

A study of the magnetic field with an unsaturated iron core in tokamak equilibrium using a spool model is described in detail. The application of this model to the J-TEXT tokamak shows that the calculated results are in good agreement with those measured experimentally. At present this scheme is used to give the plasma configuration during J-TEXTs operation.