The transition from ion to electron sheath near a floating plate aligned parallel to magnetic field

Abstract Magnetized plasma sheaths when the wall is strictly parallel to the magnetic field have never been experimentally investigated. This paper presents the measurements of potential profiles within sheaths adjacent to an unbiased (floating) stainless-steel plate (electrode) aligned exactly parallel to the magnetic field lines in a magnetized plasma device. The results reveal that the plate’s floating potential (wall potential relative to bulk plasma) undergoes a polarity inversion, changing from negative to positive values with increasing magnetic strength; that is, the sheath profile undergoes a transition from the classical ion sheath in the low-field cases to the electron sheath in the relatively high-field cases. In the transition region (magnetic strength between 135−225 G in this experiment), the sheath almost vanishes. Moreover, the ion sheath depth decreases, but the electron sheath depth increases with increasing magnetic strength. However, the thicknesses of both the ion and electron sheaths decrease with increasing magnetic strength. In addition, a smaller electrode is in disfavor of the electron sheath formation, which is opposed to the unmagnetized case. This study is important for a deeper understanding of the plasma-wall transition in magnetized plasmas.