Table of contents

Extreme ultraviolet (EUV) spectroscopy has been developed for impurity diagnostics in HL-2A tokamak. The EUV spectrometer consists of an entrance slit, a holographic varied-line-space (VLS) grating, a back-illuminated charge-coupled device (CCD) and a laser light source for optical alignment. Spectral lines in wavelength region of 20-500 Å observed from HL-2A plasmas were analyzed to study the impurity behavior. Spectral and temporal resolutions used for the analysis were 0.19 Å at CV (2×33.73 Å) and 6 ms, respectively. It was found that carbon, oxygen and iron impurities were usually dominant in the HL-2A plasma. They almost disappeared when the siliconization was carried out. Although the EUV spectra were entirely replaced by the silicon emissions just after the siliconization, the emissions were considerably decreased with accumulation of discharges. Aluminum and neon were externally introduced into the HL-2A plasma based on laser blow-off (LBO) and supersonic molecular beam injection (SMBI) techniques for a trial of the impurity transport study, respectively. The preliminary result is presented for time behavior of EUV spectral lines.

An upgraded infrared (IR) imaging system which provides a wide field of view (FOV) has been installed on the Experimental Advanced Superconducting Tokamak (EAST) to monitor the surface temperatures on plasma facing components. Modified magnetic topology induced by lower hybrid wave (LHW) can lead to the formation of striated heat flux (SHF) on divertor plates which can be clearly observed by IR camera. In this paper, LHW power modulation is applied to analyze the appearance of SHF. It is also demonstrated that deuterium (D) pellet injection and supersonic molecular beam injection (SMBI) can to some extent reduce the heat flux on the outer strike point (OSP), but enhance the SHF on lower outer plates (LOP) of divertor. This may provide an optional approach to actively control the distribution of heat flux on diveror plates, which can protect materials from long duration high-heat flux.

Ar/CH₃OH and Ar/N₂/CH₃OH plasma jets were generated at atmospheric pressure by dual-frequency excitations. Two different cases were studied with focus laid on the generation of CN radicals. In one case Ar gas passed through a bubbler with saturated methanol steam but without addition of N₂ (Ar/CH₃OH plasma). In the other case N₂ passed through the bubbler with saturated methanol steam (Ar/N₂/CH₃OH plasma). The optical emission lines of CN radicals have been observed in these two cases of plasma discharges. The addition of N₂ can significantly increase the optical emission intensity of CN bands.

One of the great difficulties in understanding nitrogen plasma elementary processes is the lack of an available database of the cross-sections of electron-impact excitations and radiations. Ab initio calculations of vibrational excitation cross sections for electron collisions with nitrogen molecules in low-lying states using similarity function approach, such as a-a', a-w, B-B' and B-W transition systems, are reported here for the first time. In the meantime, the average excitation energies of neighboring levels of these systems have been calculated. In order to obtain the cross sections, accurate spectroscopic constants and transition dipole moments have been investigated. Potential energy curves and other electronic transition dipole moments for the low-lying states of N₂ have been re-evaluated using complete active space self-consistent field (CASSCF) approach with aug-cc-pVqZ basis set. The calculated cross-sections could provide a database for studying the elementary processes and the properties in N₂ plasma.

As a spatially extended dissipated system, atmospheric-pressure dielectric barrier discharges (DBDs) could in principle possess complex nonlinear behaviors. In order to improve the stability and uniformity of atmospheric-pressure dielectric barrier discharges, studies on temporal behaviors and radial structure of discharges with strong nonlinear behaviors under different controlling parameters are much desirable. In this paper, a two-dimensional fluid model is developed to simulate the radial discharge structure of period-doubling bifurcation, chaos, and inverse period-doubling bifurcation in an atmospheric-pressure DBD. The results show that the period-2n (n = 1, 2...) and chaotic discharges exhibit nonuniform discharge structure. In period-2n or chaos, not only the shape of current pulses doesn't remains exactly the same from one cycle to another, but also the radial structures, such as discharge spatial evolution process and the strongest breakdown region, are different in each neighboring discharge event. Current-voltage characteristics of the discharge system are studied for further understanding of the radial structure.

An improved surface wave plasma source equipped with a cylindrical quartz rod has been developed, which has great potential in processing inner wall of cylindrical workpieces. A cylindrical quartz rod not only excites the plasma around the rod, but also guides surface wave plasma along the rod. The distributions of plasma density and plasma temperature under different incident microwave powers and pressures are diagnosed by a Langmuir probe. The electron density near the rod is around the order of 10¹¹cm⁻³. When the incident power is 450 W, the length of surface wave plasma column can reach up to 420 mm at 20 Pa.

The electronic excitation temperature of a surface dielectric barrier discharge (DBD) at atmospheric pressure has been experimentally investigated by optical emission spectroscopic measurements combined with numerical simulation. Experiments have been carried out to determine the spatial distribution of electric field by using FEM software and the electronic excitation temperature in discharge by calculating ratio of two relative intensities of atomic spectral lines. In this work, we choose seven Ar atomic emission lines at 415.86 nm [(3s²3p⁵)5p → (3s²3p⁵)4s] and 706.7 nm, 714.7 nm, 738.4 nm, 751.5 nm, 794.8 nm and 800.6 nm [(3s²3p⁵)4p → (3s²3p⁵)4s] to estimate the excitation temperature under a Boltzmann approximation. The average electron energy is evaluated in each discharge by using line ratio of 337.1 nm (N₂(C³Π_u →B³Π_g)) to 391.4 nm (N₂⁺(B²Σ⁺_u →X²Σ⁺_g)). Furthermore, variations of the electronic excitation temperature are presented versus dielectric thickness and dielectric materials. The discharge is stable and uniform along the axial direction, and the electronic excitation temperature at the edge of the copper electrode is the largest. The corresponding average electron energy is in the range of 1.6–5.1 eV and the electric field is in 1.7–3.2 MV/m, when the distance from copper electrode varies from 0 cm to 6 cm. Moreover, the electronic excitation temperature with a higher permittivity leads to a higher dissipated electrical power.

Pulsed discharge plasma has exhibited active potential to prepare low molecular weight chitosan. In the present study, the viscosity of chitosan solution was decreased noticeably after treated with pulsed corona discharge plasma. An experimental investigation on electrical characteristics of pulsed corona discharge plasma in chitosan solution was conducted with a view toward getting insight into discharge process. Factors affecting I–V curve, single pulse injection energy and pulse width were studied. Experimental results showed positive effect of pulsed peak voltage on discharge plasma in chitosan solution. Pulse-forming capacitor greatly influenced the discharge form, and 4 nF was observed as a suitable value for efficiently generating stable discharge plasmas. As the electrode distance was larger than 10 mm, it had slight impact on discharge plasma due to the excellent conductive-property of chitosan solution. The injection energy significantly increased with air flow rate, while the pulse width hardly changed as the air flow rate increased from 0.5 m³/h to 1.0 m³/h. This study is expected to provide reference for promoting the application of pulsed corona discharge plasma to chitosan solution treatment.

The field electron emission plays a vital role in the process of vacuum discharge breakdown. The electric field strength at the cathode tip is significant to the generation characteristics of vacuum arc metal plasmas. To increase the field strength at the cathode tip, a coaxial electrode plasma source was employed with an insulator settled between the electrodes. The math expression of the field strength is derived based on the Gauss theory. The impact of the insulator on the electric field and parameters of plasmas were investigated by MAXWELL 3D® simulation software and the Langmuir probe. In addition, a composite insulator was adopted to further strengthen the field strength. A series of experiments were performed to focus on the role of the composite insulator in detail. The experimental and simulation results indicate that, a reasonable layout of the insulator, especially the composite insulator, can effectively increase the field strength at the cathode tip and the plasma density.

A highly-sensitive in-situ diagnosis approach for nitrogen dioxide (NO₂) has been developed in dielectric barrier discharge (DBD) based on pulsed cavity ring-down spectroscopy (CRDS). Absorption bands of NO₂ in a spectral region from 508 nm to 509 nm were used, and a detection limit of 17.5 ppb was achieved. At this level of sensitivity, the quantitative and real-time monitoring of the production and removal of NO₂ are accomplished for the first time in the discharge region. By measuring the removal amount and rate at different NO₂ initial number densities from 1.54 × 10¹³ cm⁻³ to 2.79 × 10¹⁴ cm⁻³, we determined the relationship between them and NO₂ initial number densities. The removal amount linearly increases with the initial number density, while the removal rate increases logarithmically. At a lower initial number density, the removal rate is limited. By considering the chemical kinetic mechanism in plasma, a qualitative explanation for the above phenomena is proposed: the additional NO₂ produced by discharge limits the removal rate, since the NO₂ concentration is dominated by the competition between the forward reactions (production) and the reverse reactions (removal).

Laser-induced breakdown spectroscopy (LIBS) is a powerful analytical tool for real-time diagnostics and detection of multiple elements deposited at the first wall of magnetically confined plasma fusion devices. Recently, we have tested LIBS in our laboratory for application to in situ real-time diagnostics in the fusion device EAST. In this study, we applied polarization-resolved LIBS (PR-LIBS) to reduce the background continuum and enhance the resolution and sensitivity of LIBS. We used aluminium (Al) (as a substitute for Be) and the first wall materials tungsten (W) and molybdenum (Mo) to investigate polarized continuum emission and signal-to-background ratio (SBR). A Nd:YAG laser with first, second and third harmonics was used to produce plasma. The effects of the laser polarization plane, environmental pressure and polarizer detection angle were investigated. The spectra obtained without using a polarizer (i.e. LIBS) were compared with those obtained with a polarizer (PR-LIBS). Distribution of emission spectral intensity was observed to follow Malus' law with respect to variation in the angle of detection of the polarizer. The spectra obtained by PR-LIBS had a higher SBR and greater stability than those obtained by LIBS, thereby enhancing the reliability of LIBS for quantitative analyses. A comparison of Al, Mo and W showed that W exhibited a higher continuum with stronger polarization than the low-Z elements.

The oxidation of elemental mercury (Hg⁰) by dielectric barrier discharge reactors was studied at room temperature, where concentric cylinder discharge reactor (CCDR) and surface discharge plasma reactor (SDPR) were employed. The parameters (e.g. Hg⁰ oxidation efficiency, energy constant, energy yield, energy consumption, and O₃ concentration) were discussed. From comparison of the two reactors, higher Hg⁰ oxidation efficiency and energy constant in the SDPR system were obtained by using lower specific energy density. At the same applied voltage, energy yield in the SDPR system was larger than that in the CCDR system, and energy consumption in the SDPR system was much less. Additionally, more O₃ was generated in the SDPR system. The experimental results showed that 98% of Hg⁰ oxidation efficiency, 0.6 J·L⁻¹ of energy constant, 13.7 μg·kJ⁻¹ of energy yield, 15.1 eV·molecule⁻¹ of energy consumption, and 12.7 μg·J⁻¹ of O₃ concentration were achieved in the SDPR system. The study reveals an alternative and economical technology for Hg⁰ oxidation in the coal-fired flue gas.

The distribution of magnetic field in Hall thruster channel has significant effect on its discharge process and wall plasma sheath characteristics. By creating physical models for the wall sheath region and adopting two-dimensional particle in cell simulation method, this work aims to investigate the effects of magnitude and direction of magnetic field and ion velocity on the plasma sheath characteristics. The simulation results show that magnetic field magnitudes have small impact on the sheath potential and the secondary electron emission coefficient, magnetic azimuth between the magnetic field direction and the channel radial direction is proportional to the absolute value of the sheath potential, but inversely proportional to the secondary electron emission coefficient. With the increase of the ion incident velocity, secondary electron emission coefficient is enhanced, however, electron density number, sheath potential and radial electric field are decreased. When the boundary condition is determined, with an increase of the simulation area radial scale, the sheath potential oscillation is aggravated, and the stability of the sheath is reduced.

Two fission chambers with different amounts of fissile material (enriched 90% uranium-235) have been manufactured for neutron flux detection in a thermonuclear fusion device. The characteristics of neutron signal and its discrimination from other signals, and a plateau of high voltage between the anode and cathode have been validated in a thermal neutron source. The energy responses of the two fission chambers at seven energy levels have been calibrated in an accelerator fast neutron source and the results agree well with the simulations.

In order to obtain enhanced plasma parameters a complete new tokamak HL-2M is now under construction in Southwestern Institute of Physics. To assure the structural safety of the device for the entire operation cycle, one of the most important issues is the lifetime-limiting effects due to the pulsed operation mode. Fatigue is one of the major failure modes to be considered in mechanical design, and pulsed operation imposes stress with significant alternating components on the support structure (SS). Therefore, the reliability of the whole device is strongly affected by the stress and fatigue characteristic of the SS as the interface structure. This article introduces the SS design and details the fatigue life calculation methods based on the different characteristics of the sub-structures. The fatigue life in hazardous areas of the toroidal field coils anti-torque structure (TFCs-ATs) has been determined by non-linear analysis results. And with the stress-time history data of the vacuum vessel & poloidal field coils support structure (VV&PFCs SS), the fatigue analysis of the hot spots has been completed based on rain-flow counting method and linear cumulative damage method. The calculated minimum fatigue life on TFCs-ATs and VV&PFCs SS is 4.743E+05 and 1.805E+06 cycles, respectively. And the calculated fatigue life on sub-structures can meet the required life for HL-2M tokamak: 1.0E+05 cycles.