Experimental insights into discharge instability and energetic ion dynamics in ampere-level hollow cathodes

Abstract This study investigates the low-frequency ionization instability, high-frequency ion acoustic turbulence, and the energy distributions of energetic ions in ampere-level hollow cathodes. The effects of discharge currents and gas flow rates on discharge instabilities and energetic ion distributions are systematically analyzed, focusing on the mechanisms of ion-acoustic waves at both low- and high-frequency. Key factors influencing the power-law ‘ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>η</mml:mi> </mml:mrow> </mml:math> ’ ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msup> <mml:mi>ϕ</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> <mml:mo>∝</mml:mo> <mml:mrow> <mml:msup> <mml:mi>ω</mml:mi> <mml:mi>η</mml:mi> </mml:msup> </mml:mrow> <mml:mo>,</mml:mo> <mml:mi>η</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:math> ) of high-frequency ion acoustic waves are identified, including electron trapping, ion resonance broadening, and the nonlinear Landau damping effect. Furthermore, the generation mechanisms of energetic ions are illustrated at the micro (e.g. anomalous collision frequency ‘ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>ν</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>an</mml:mtext> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mtext>IAT</mml:mtext> </mml:mrow> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> ’ induced by IAT) and macro (e.g. discharge voltage) levels. Correlation analysis reveals the relationships between energetic ions, low-frequency ionization instabilities, and high-frequency ion acoustic turbulence. These findings offer valuable insight into the unstable discharge oscillations of ampere-level hollow cathodes and the generation of energetic ions. It provides guidance for optimizing the discharge parameters of hollow cathodes, thus improving the endurance and stability of the cathode.