Kinetic simulation of anomalous skin effect in low-pressure inductively coupled plasmas

The plasma characteristics and nonlocal electron dynamics at 27.12 and 40.68 MHz in miniature inductively coupled argon plasmas are investigated using a two-dimensional implicit particle-in-cell/Monte Carlo collision model. At a very low pressure, energetic electrons from the skin layer interact nonlocally with the inductive electric field, resulting in alternating positive and negative power absorption regions at all driving frequencies. These energetic electrons gain energy in positive and lose energy in negative power absorption regions, forming anomalous current density peaks (i.e., current layers) at the interfaces between these regions. Increasing the chamber height and driving frequency are both found to promote the development of multiple current layers. Since the inductive electric field distribution is a superposition of the coil-induced field and the plasma current-induced field, current layers with high current density can significantly modulate the field. Particularly at a chamber height of 6 cm and a driving frequency of 40.68 MHz, the plasma current can induce an anomalous phase reversal of the local inductive electric field and locally disrupt the typical alternating pattern of positive-negative power absorption (manifested as two consecutive positive power peaks in space), which thereby induces positive power absorption over a broad spatial range. These findings provide critical insights into the low-pressure nonlocal electron dynamics, offering valuable guidance for optimizing plasma sources in applications.