Rawat Arti, Ganguli A, Narayanan Ramesh, Tarey R D
Department of Energy Science and Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India.
Rev Sci Instrum. 2023 Jun 1;94(6). doi: 10.1063/5.0144354.
This paper reports an indigenously developed probe for the measurement of spatial profiles of the absorbed/generated RF power density Pabs (W/m3) in RF discharges. The technique utilizes a calibrated current (J) probe based on the Rogowski coil principle and an electric field (E) probe based on capacitive coupling, both integrated into a single probe called the J.E probe. Various aspects of the probe, such as its design, fabrication, calibration, and limitations, were resolved before it was used for obtaining axial profiles of RF power absorption/generation. Also presented are the first experimental results for the absorbed power density profiles at the fundamental (13.56 MHz) and harmonic (27.12 MHz) along the length of a capacitively coupled discharge. The axial scans between the powered and grounded electrode were taken at different argon gas pressures (10-800 mTorr) at a fixed RF power of 10 W. Detailed analysis of the results shows that even for systems with large electrode gaps, i.e., plasmas with long bulk plasma regions, practically all the fundamental power is absorbed in a narrow edge region near the powered electrode, irrespective of the pressure. Absorption is high near the RF electrode since the RF fields peak in this region. Another important conclusion is that stochastic absorption of the fundamental and harmonic generation proceeds fairly efficiently in the vicinity of the powered electrode even at high pressures. It may be mentioned that the probe technique introduced here is the first of its kind, and although there is considerable scope for miniaturization, it has, nonetheless, provided some key insights into the nature of RF power absorption in capacitive discharges.
本文报道了一种自主研发的探头，用于测量射频放电中吸收/产生的射频功率密度Pabs（W/m³）的空间分布。该技术利用了基于罗果夫斯基线圈原理的校准电流（J）探头和基于电容耦合的电场（E）探头，二者集成在一个称为J.E探头的单一探头中。在将该探头用于获取射频功率吸收/产生的轴向分布之前，解决了其设计、制造、校准及局限性等各个方面的问题。文中还给出了在电容耦合放电的长度方向上，基频（13.56 MHz）和谐频（27.12 MHz）下吸收功率密度分布的首批实验结果。在10 W的固定射频功率下，于不同氩气压力（10 - 800 mTorr）下对有源电极和接地电极之间进行轴向扫描。对结果的详细分析表明，即使对于电极间距较大的系统，即具有长体等离子体区域的等离子体，实际上所有的基频功率都在靠近有源电极的狭窄边缘区域被吸收，与压力无关。由于射频场在该区域达到峰值，所以在射频电极附近吸收较高。另一个重要结论是，即使在高压下，基频的随机吸收和谐波的产生在有源电极附近也相当高效地进行。需要提及的是，这里介绍的探头技术是首创的，尽管有相当大的小型化空间，但它 nonetheless 为电容性放电中射频功率吸收的本质提供了一些关键见解。
