Experimental investigation on low frequency instability in a fireball plasma sustained by a surrounding double layer

Abstract A spontaneous global oscillation with frequency <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> </mml:math> ∼ 40 kHz is observed in a fireball-assisted by a double layer formed surrounding the fireball. The cause of the instability is associated with the oscillation of ions trapped in the fireball. The electron sheath at the electrode end and the positive space charge region of the double layer provides the platform for ion oscillation which are initially drifting towards the electron sheath. An external signal with frequency close to the spontaneous instability frequency is coupled to explore the nonlinear interaction. The growth of a small amplitude external signal and modulation leading to the suppression of the spontaneous oscillation confirm the instability and its nonlinear interaction with the external signal. The interaction dynamics have been found to follow the forced Van der Pol equation.