射频空心阴极放电中电子加热机制的实验研究

在氩气环境下对射频驱动下空心阴极的放电特性进行了实验研究,得到了不同工作条件下射频空心阴极放电中的电子密度、电子能量几率分布函数等结果。研究结果表明,相比于平板电极容性耦合射频放电,空心结构电极的射频放电能获得更高的电子密度。在形成空心阴极效应后,等离子体密度随电压、气压的升高而增大。通过EEPF进一步分析了射频空心阴极放电电子加热机制随p D值、工作电压的变化。发现当p D增加时,射频空心阴极放电中电子加热机制从以振荡鞘层对高能电子的随机加热为主逐渐转变为对等离子体中电子的欧姆加热为主;当逐渐提升电压时,电子本身获得能量机制则由开始的欧姆加热转到了向后来的随机加热。

Evolution of plasma parameters in an Ar-N2/He inductive plasma source with magnetic pole enhancement

Magnetic pole enhanced inductively coupled plasmas （MaPE-ICPs） are a promising source for plasma-based etching and have a wide range of material processing applications. In the present study Langmuir probe and optical emission spectroscopy were used to monitor the evolution of plasma parameters in a MaPE-ICP Ar-Na/He mixture plasma. Electron density （ne） and temperature （Te）, excitation temperature （Texc）, plasma potential （Vp）, skin depth （6） and the evolution of the electron energy probability function （EEPF） are reported as a function of radiofrequency （RF） power, pressure and argon concentration in the mixture. It is observed that ne increases while Te decreases with increase in RF power and argon concentration in the mixture. The emission intensity of the argon line at 750.4 nm is also used to monitor the variation of the ‘high-energy tail＇ of the EEPF with RF power and gas pressure. The EEPF has a ‘bi-Maxwellian＇ distribution at low RF powers and higher pressure in a pure N2 discharge. However, it evolves into a ‘Maxwellian＇ distribution at RF powers greater than 70 W for pure N2, and at 50 W for higher argon concentrations in the mixture. The effect of argon concentration on the temperatures of two electron groups in the ‘bi-Maxwellian＇ EEPF is examined. The temperature of the low-energy electron group TL shows a decreasing trend with argon addition until the ‘thermalization＇ of the two temperatures occurs, while the temperature of high-energy electrons Ta decreases continuously.

Characteristics of inductively coupled plasma(ICP)and helicon plasma in a single-loop antenna

Large area uniform plasma sources,such as high-density magnetized inductively coupled plasma(ICP)and helicon plasma,have broad applications in industry.A comprehensive comparison of ICP and helicon plasma,excited by a single-loop antenna,is presented in this paper from the perspectives of mode transition,hysteresis behavior,and density distribution.The E-H mode transition in ICP and the E-H-W mode transition in helicon plasma are clearly observed in the experiments.Besides,the considerable variation of hysteresis behavior from inverse hysteresis to normal hysteresis by the influence of the magnetic field is explored.The bi-Maxwellian and Maxwellian electron energy distribution functions in each discharge are used to explain this phenomenon,which is essentially related to the transition from a nonlocal kinetic property to a local kinetic property of electrons.In addition,we notice that the plasma density,in the radial direction,is peaked in the center of the tube in ICP,but a complicated distribution is formed in helicon plasma.In the axial direction,the maximum plasma density is still in the center of the antenna in ICP,whereas the highest plasma density is located downstream,far away from the antenna,in helicon plasma.It is believed that the reflected electrons in the sheath and pre-sheath by the upper metallic endplate and downstream propagated helicon wave will be responsible for this plasma density profile in helicon plasma.Due to the constrained electron motion in the magnetic field,an extremely uniform density distribution will be obtained with an appropriate axial magnetic field in the wave discharge mode.

Experimental study of sheath potential coefficient in the J-TEXT tokamak

Sheath potential coefficient α is a key parameter, which is used to estimate plasma potential(Vp)for edge plasma physics study. Recently, a series of experiments has been carried out under hydrogen plasmas in the J-TEXT tokamak with swept probe, which is employed for current–voltage(I–V) characteristic measurement. Electron temperature is evaluated from I–V curve by three-parameter fitting method, and the electron energy probability function shows that electron distribution is Maxwellian both outside and inside of last closed flux surface(LCFS). Plasma potential is obtained by crossing point between I–V exponential fitting curve and electron saturation current extrapolating line, which is in good agreement with first derivative probe technique. The α coefficient profile in the vicinity of the LCFS is obtained, which is in the range of 2.1–3, and decreases from outside to inside of LCFS.

SG滤波在朗缪尔探针信号处理中的应用

利用朗缪尔探针检测射频耦合等离子体特性参数时,测得的伏安特性曲线会受电磁干扰而产生畸变,从而影响等离子体参数的计算和特性分析。为此,利用Savitzky-Golay(SG)滤波算法对伏安特性曲线进行分段滤波,给出平滑效果较好的特性参数。实验结果表明,SG算法对原始信号特征改变较少,求出的电子能量概率函数准确度较高。