Park Sanghoo, Choe Wonho, Kim Holak
Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea.
Department of Physics, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea.
Sci Rep. 2018 Jul 5;8(1):10217. doi: 10.1038/s41598-018-27945-6.
Electron heating is a fundamental and multidisciplinary phenomenon in partially ionized gases, from the planet's ionosphere to laboratory-scale plasmas. Plasmas produced at ambient or reduced pressures have recently shown potential for scientific and industrial applications. However, electron heating, which is strongly coupled to the physicochemical properties of these plasmas, has been poorly understood. We experimentally found the rapid structural transition from non-local to local electron heating in collisional radio-frequency discharges at atmospheric-to-subatmospheric pressures. As the gas pressure decreased from 760 to 200 Torr, the time-averaged electron density increased from 1.3 × 10 to 1.3 × 10 cm, and the electron temperature decreased from 2.5 to 1.1 eV at the maximum allowable discharge current in the abnormal α-mode in the plasma bulk. The spatiotemporal evolution of the electron temperature clearly shows that the electron temperature increases uniformly throughout the bulk plasma region during sheath expansion and collapse at 760 Torr, but the electron heating weakens with sheath collapse as the gas pressure decreases.
电子加热是部分电离气体中的一种基本且多学科的现象，涵盖从地球电离层到实验室规模的等离子体。在环境压力或减压条件下产生的等离子体最近已显示出在科学和工业应用方面的潜力。然而，与这些等离子体的物理化学性质紧密相关的电子加热，目前仍未得到充分理解。我们通过实验发现，在大气压力至亚大气压力的碰撞射频放电中，电子加热存在从非局部到局部的快速结构转变。随着气体压力从760托降至200托，在等离子体主体的异常α模式下，在最大允许放电电流时，时间平均电子密度从1.3×10增加到1.3×10厘米，电子温度从2.5电子伏特降至1.1电子伏特。电子温度的时空演化清楚地表明，在760托时，在鞘层膨胀和坍缩期间，整个等离子体主体区域的电子温度均匀升高，但随着气体压力降低，电子加热在鞘层坍缩时减弱。
