[en] Here, the high magnetic field helicon experiment system is a helicon wave plasma (HWP) source device in a high axial magnetic field (B₀) developed for plasma–wall interactions studies for fusion reactors. This HWP was realized at low pressure (5 × 10^–3 – 10 Pa) and a RF (radio frequency, 13.56 MHz) power (maximum power of 2 kW) using an internal right helical antenna (5 cm in diameter by 18 cm long) with a maximum B 0 of 6300 G. Ar HWP with electron density ~10¹⁸–10²⁰ m^–3 and electron temperature ~4–7 eV was produced at high B₀ of 5100 G, with an RF power of 1500 W. Maximum Ar+ ion flux of 7.8 × 10²³ m^–2 s^–1 with a bright blue core plasma was obtained at a high B₀ of 2700 G and an RF power of 1500 W without bias. Plasma energy and mass spectrometer studies indicate that Ar⁺ ion-beams of 40.1 eV are formed, which are supersonic (~3.1c _s). The effect of Ar HWP discharge cleaning on the wall conditioning are investigated by using the mass spectrometry. And the consequent plasma parameters will result in favorable wall conditioning with a removal rate of 1.1 × 10²⁴ N₂/m²h.

[en] A new edge tangential multi-energy soft x-ray (ME-SXR) diagnostic with high temporal (≤ 0.1 ms) and spatial (∼1 cm) resolution has been developed for a variety of physics topics studies in the EAST tokamak plasma. The fast edge electron temperature profile (approximately from $r/a\sim <!--\; ???\; -->0.6$ to the scrape-off layer) is investigated using ME-SXR diagnostic system. The data process was performed by the ideal ‘multi-foil’ technique, with no priori assumptions of plasma profiles. Reconstructed ME-SXR emissivity profiles for a variety of EAST experimental scenarios are presented here for the first time. The applications of the ME-SXR for study of the effects of resonant magnetic perturbation on edge localized modes and the first time neon radiating divertor experiment in EAST are also presented in this work. It has been found that neon impurity can suppress the 2/1 tearing mode and trigger a 3/1 MHD mode. (paper)

[en] Through the use of a reductive perturbation technique, solitary kinetic Alfvén waves (KAWs) are investigated in a low but finite $\mathrm{\beta <!--\; ??\; -->}$ (particle-to-magnetic pressure ratio) dense electron–positron–ion plasma where electrons and positrons are degenerate. The degenerate plasma model considered here permits the existence of sub-Alfvénic compressive solitary KAWs. The influence of r (equilibrium positron-to-ion density ratio), ${\mathrm{\sigma <!--\; ??\; -->}}_{\mathrm{F}}$ (electron-to-positron Fermi temperature ratio), $\mathrm{\beta <!--\; ??\; -->}$ and obliqueness parameter $l_z$ on various characteristics of solitary KAWs are examined through numerical plots. We have shown that there exists a critical value of $l_z$ at which a soliton width attains its maximum value which decreases with an increase in r and ${\mathrm{\sigma <!--\; ??\; -->}}_{\mathrm{F}}.$ It is also found that solitons with a higher energy propagate more obliquely in the direction of an ambient magnetic field. The results of the present investigation may be useful for understanding low frequency nonlinear electromagnetic wave propagation in magnetized electron–positron–ion plasmas in dense stars. Specifically, the relevance of our investigation to a pulsar magnetosphere is emphasized. (paper)

[en] This work presents the first electrical and optical measurements of the initial phase of hydrogen discharge in the upgraded spherical tokamak GLAST-III, initiated with electron cyclotron heating (ECH). Diagnostic measurements provide insights into expected and unexpected physics issues related to the initial phase of discharge. A triple Langmuir probe (TLP) has been developed to measure time series of the floating potential, plasma electron temperature and number density over the entire discharge, allowing monitoring of the two phases of the discharge: the ECH pre-ionization phase following by the plasma current formation phase. A TLP has the ability to give time-resolved measurements of the floating potential (V _float), electron temperature (T _e) and ion saturation current $(I_{\mathrm{s}\mathrm{a}\mathrm{t}}\propto <!--\; ???\; -->n_{\mathrm{e}}\surd <!--\; ???\; -->k{T}_{\mathrm{e}}).$ The evolution of the ECH-assisted pre-ionization and subsequent plasma current phases in one shot are well envisioned by the probe. Intense fluctuations in the plasma current phase advocate for efficient equilibrium and feedback control systems. Moreover, the emergence of some strong impurity lines in the emission spectrum, even after only a few shots, suggests a crucial need for improvements in the base vacuum level. A noticeable change in the shape of the temporal profiles of the floating potential, electron temperature, ion saturation current (I _sat) and light emission has been observed with changing hydrogen fill pressure and vertical magnetic field. (paper)

[en] The general dispersion of tearing modes due to the effects of electron inertia and resistivity in pair plasmas is derived analytically, and is discussed in two cases: ${△<!--\; ???\; -->}^{\mathrm{\prime <!--\; ???\; -->}}\gg <!--\; ???\; -->1$ and ${△<!--\; ???\; -->}^{\mathrm{\prime <!--\; ???\; -->}}\ll <!--\; ???\; -->1$, where ${\mathrm{\Delta <!--\; ??\; -->}}^{\mathrm{\prime <!--\; ???\; -->}}$ is the instability criterion of the tearing mode. It is found that the conditions under which either resistivity or electron inertia dominates depend strongly on the limit of ${\mathrm{\Delta <!--\; ??\; -->}}^{\mathrm{\prime <!--\; ???\; -->}}$ considered. (paper)

[en] A kind of dielectric barrier discharge (DBD) device composed of water electrodes with 3 × 3 forms can produce large-area low-temperature plasmas at atmospheric pressure. To reflect the discharge characteristics of DBD better, a dynamic simulation model, which is based on the voltage controlled current source (CCS), is established, then the established model in Matlab/Simulink is used to simulate the DBD in air. The voltage–current waves and Lissajous at a voltage of 10 kV, 11 kV and 12 kV peak value with a frequency of 15 kHz are studied. The change of the discharge power of DBD with a different amplitude and frequency of applied voltage is also analyzed. The result shows the voltage–current waves, Lissajous and discharge power of DBD under different conditions from the simulation agree well with those of the experiment. In addition, we propose a method to calculate the dielectric barrier capacitance $C_{\mathrm{d}}$ and the gap capacitance $C_{\mathrm{g}},$ which is valid through analyzing the variation of capacitance at different voltage amplitudes. (paper)

[en] Poloidal field (PF) converters provide controlled DC voltage and current to PF coils. The many harmonics generated by the PF converter flow into the power grid and seriously affect power systems and electric equipment. Due to the complexity of the system, the traditional integral operation in Fourier analysis is complicated and inaccurate. This paper presents a piecewise method to calculate the harmonics of the ITER PF converter. The relationship between the grid input current and the DC output current of the ITER PF converter is deduced. The grid current is decomposed into the sum of some simple functions. By calculating simple function harmonics based on the piecewise method, the harmonics of the PF converter under different operation modes are obtained. In order to examine the validity of the method, a simulation model is established based on Matlab/Simulink and a relevant experiment is implemented in the ITER PF integration test platform. Comparative results are given. The calculated results are found to be consistent with simulation and experiment. The piecewise method is proved correct and valid for calculating the system harmonics. (paper)

[en] A simple gas-liquid diaphragm discharge reactor was designed and characteristics of the discharge and its application on decolorization of brilliant red B in an aqueous solution were investigated. The results showed that strong oxidizing agents such as ·OH and ·O radicals were generated. Average electron temperature of the discharge was 0.72 eV, 1.15 eV and 0.83 eV with air, oxygen and argon as the discharge gas, respectively. Solution pH and conductivity changed little when oxygen or argon was used as the discharge gas; however, these two parameters changed significantly when the discharge was performed in air. During the discharge treatment, the characteristic absorption peaks of brilliant red B gradually decreased where the decolorization followed the first-order kinetics. With 10 min of discharge, the decolorization of brilliant red B (30 mg L⁻¹) can reach 96%, 81% and 62% in the cases of oxygen, argon and air, respectively. The analysis of by-products showed that the brilliant red B molecule can be effectively destroyed in this discharge mode. (paper)

[en] As advanced linear plasma sources, cascaded arc plasma devices have been used to generate steady plasma with high electron density, high particle flux and low electron temperature. To measure electron density and electron temperature of the plasma device accurately, a laser Thomson scattering (LTS) system, which is generally recognized as the most precise plasma diagnostic method, has been established in our lab in Dalian University of Technology. The electron density has been measured successfully in the region of 4.5 × 10¹⁹ m⁻³ to 7.1 × 10²⁰ m⁻³ and electron temperature in the region of 0.18 eV to 0.58 eV. For comparison, an optical emission spectroscopy (OES) system was established as well. The results showed that the electron excitation temperature (configuration temperature) measured by OES is significantly higher than the electron temperature (kinetic electron temperature) measured by LTS by up to 40% in the given discharge conditions. The results indicate that the cascaded arc plasma is recombining plasma and it is not in local thermodynamic equilibrium (LTE). This leads to significant error using OES when characterizing the electron temperature in a non-LTE plasma. (paper)

[en] This paper discusses the conversion of nitric oxide (NO) with a low-temperature plasma induced by a catalytic packed-bed dielectric barrier discharge (DBD) reactor. Alumina oxide (Al₂O₃), glass (SiO₂) and zirconium oxide (ZrO₂), three different spherical packed materials of the same size, were each present in the DBD reactor. The NO conversion under varying input voltage and specific energy density, and the effects of catalysts (titanium dioxide (TiO₂) and manganese oxide (MnO _x ) coated on Al₂O₃) on NO conversion were investigated. The experimental results showed that NO conversion was greatly enhanced in the presence of packed materials in the reactor, and the catalytic packed bed of MnO _x /Al₂O₃ showed better performance than that of TiO₂/Al₂O₃. The surface and crystal structures of the materials and catalysts were characterized through scanning electron microscopy analysis. The final products were clearly observed by a Fourier transform infrared spectrometer and provided a better understanding of NO conversion. (paper)