Observation Of Ionization-like Instability In A Linear Plasma Device

Ionization instability, also known as breathing mode oscillation, is one of the predominant instabilities generally observed in Hall thrusters [1] which deteriorates their performance. It is a low-frequency longitudinal oscillation mode that arises due to the periodic depletion of neutral atoms in the ionization area. A lot of studies have been done on this instability mostly through simulation. However, experimental study on it is limited, mainly due to the limitation of the use of probes in hall thrusters and the simultaneous occurrence of this mode with various other low-frequency azimuthal modes [2]. 

Different waves and instabilities occurring in plasma can be studied in a well-controlled setting in linear plasma devices. For the purpose of precisely examining the different waves and instabilities, an indigenous linear plasma device (1.1 m in length and 25 cm in diameter) producing uniform and quiescent plasma by hot cathode discharge has been fabricated in-house at the Institute of Advanced Study in Science and Technology (IASST) [3]. A high degree of quiescence (δn/n < 0.5 %) was measured in the neutral pressure range of 1×10⁻⁴−1×10⁻³ mbar. However, the onset of certain instabilities results in a reduced value of plasma quiescence beyond this neutral pressure range. Investigation of the fluctuations observed in floating potential, discharge current, and density with filling neutral pressure shows the appearance of low-frequency oscillations at lower filling neutral pressure. The frequency of these oscillations is in the range of ionization instability. Detailed results of this study will be presented. 

 

References:

[1] J-P Boeff and L. Garrigues, J. Appl. Phys., 84, 3541 (1998)

[2] E. Y. Choueiri, Physics of Plasmas, 8(4), 1411-1426 (2001)

[3] D. Bora, A. Tarafder, S. Biswas, et. al., Phys. Scr. 98, 045618 (2023)