The ICP in closed quartz chamber is an effective solution to local stealth of aircraft .The attenuation of the electromag‐netic wave is strongly affected by distribution of electron density in incidence direction .In this paper ,an experiment that the pla‐nar ICP discharged in all‐quartz chamber (30.8 cm × 30.8 cm × 5.8 cm) was conducted .The E‐H mode transition of Ar/Air ICP was observed ,and the width and the proportion of ICP area versus the RF power were measured .Such physical phenomena were explained rationally by ICP‐source theoretical model .A new microwave diagnostics is presented based on the Hβspectrum broad‐ening and the characteristics of planar‐coil ICP .It is used to diagnose the spatial electron density distribution of Ar/Air in inci‐dence direction .The parameters of electron density distribution function in the incident direction are separately solved by the fit‐ting results of the Hβstack broadening and microwave interferometer .And the curves of electron density distribution versus RF power are obtained .We obtain a stable ring plasma source with electron density varying from 0.5 × 1011 ~3.2 × 1011 cm -3 .The experiment demonstrates that electron density is prominently affected by the RF power and gas species .The peak value of electron density is positioned near the center of ICP .It is shown that the electron density of Ar ICP is higher than the air ,but the area of air ICP is larger through comparing the curves of Ar/Air electron density .%闭式腔体IC P是解决飞行器等离子体局部隐身的可行方案，其电子密度N e在电磁波入射方向上的分布是影响其电磁波衰减效果的关键因素。对此，开展了在30.8 cm ×30.8 cm ×5.8 cm石英腔体内的IC P放电实验，通过实验研究了空气／氩气IC P的 E‐H模式跳变的物理现象，通过测量得到了空气／氩气环状IC P的宽度和覆盖面积比例随电源功率变化的规律，并给出了上述实验现象的理论解释。为了得到平面型IC P的电子密度在微波入射方向的分布，提出基于 Hβ光谱展宽的微波干涉分布诊断法，分别对平面真空腔室内空气／氩气ICP的电子密度在电磁波入射方向上的分布进行了诊断，通过 Hβ（486.13 nm） Stark展宽拟合和微波干涉过程分别获取电子密度分布函数的两项参数，得到了电子密度分布随放电功率变化的曲线。实验可得到电子密度范围为0.5×1011～3.2×1011 cm －3的环状ICP源，实验结果表明，ICP的电子密度受气体种类，射频功率影响较大，峰值电子密度接近IC P的中心位置，通过比较发现，氩气的电子密度较高，有效拟合区域较窄，空气的有效拟合区域较宽，覆盖面积较大。
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