在详细考虑电化学反应和粒子碰撞关系的基础上,建立了螺旋波放电三维直接数值计算模型,舍弃以往模型小扰动假设,对Maxwell方程组直接求解以计算电磁场能量沉积份额,扩展了螺旋波等离子体计算模型的精度和适用范围.以Ar为工质气体的仿真结果显示:密度跃升效应和电子温度与放电压力的关系与Toki等和Chen的实验结果符合较好;与经典鞘层理论对比,在粒子数密度、德拜长度、电势以及电子温度的分布上取得高度一致,验证了模型的有效性和精度.利用本文模型研究了低场螺旋波放电过程中的磁场峰值现象,验证了放电室端面的波干涉机理,并发现波干涉的本质是螺旋波分量与其端面回波叠加形成的驻波.%With the detailed consideration of electrochemical reactions and collision relations,a direct numerical simulation model of helicon plasma discharge with three-dimensional fluid-dynamic equations is proposed in the present work.It can improve the precision of results and widen the model applicability by discarding the small perturbation theory in previous helicon models which are partially analytical in essence.Under the assumption of weak ionization,the Maxwell equations coupled with the plasma parameters are directly solved in the whole computational domain.Thus the energy deposited from electromagnetic wave to plasma can be then easily calculated.The values of plasma parameters which include electron density,mean electron energy and heavy species density are obtained by solving a set of drift-diffusion equations.Meanwhile,seven kinds of chemical reactions in the plasma and two kinds of surface reactions on the wall are taken into account.All of the partial differential equations are solved by the finite element solver of COMSOL MultiphysicsTM with the full coupled method.The results of numerical cases employing argon as the working medium show that there exists a sharp density jump from a low to high value as the radiofrequency power is raised.The density jump phenomenon is in accordance with the experimental results of Toki (Toki K,Shinohara S,Tanikawa T,Shamrai K P 2006 Thin Solid Films 506-507 597) and Chen (Chen F F 2007 Plasma Sources Sci.Technol.16 593).The electron temperature decreases with an increase of the gas pressure,which is similar to Toki's (Toki K,Shinohara S,Tanikawa T,Shamrai K P 2006 Thin Solid Films 506-507 597) measurement by a RF compensation probe.In comparison with the classical sheath theory,the simulation result demonstrates that the distribution of parameters such as particle number density,the Deby length,electric potential and electron temperature can be solved exactly.In addition,the phenomenon of low-field density peak in helicon discharge was studied in the work.Previous research by Chen (Chen F F 2003 Phys.Plasmas 10 2586) suggests that this peak is caused by constructive interference from the reflected wave.The effect of length of the discharge chamber on the relation of electron density and background magnetic field is investigated numerically.The results validate the mechanism of wave interference reflected by endplates of the discharge chamber.Furthermore,the time-averaged magnetic energy density has more than one peak on the axial direction.Comparing the distribution of the magnetic energy density to that of the dimensionless amplitude of the helicon wave and the TG wave in the one-dimensional undamped condition,it found that the length of peak to peak of the helicon wave is just as twice as that of the magnetic energy density,which indicates that the substance of wave interference is involved in the standing wave generated by the helicon wave and its reflected wave from endplates.
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