Parametric decays into trapped microwaves in low-temperature laboratory plasmas

Abstract In the past decades, observations from magnetically confined fusion experiments have revealed instances of two-plasmon decay instabilities between injected X-mode waves for second harmonic electron cyclotron heating and trapped upper hybrid (UH) waves near half frequency of the injected wave. In this study, we demonstrate that developed models used to assess the two-plasmon decay instability in fusion plasmas are also applicable to general low-temperature laboratory plasmas. We carry out a parameter scan where a reduced analytical model is used to find optimal plasma conditions for the growth rates of the instability for an injected X-mode wave with frequency of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>5.8</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>GHz</mml:mi> </mml:mrow> </mml:mrow> </mml:math> . To verify the behaviour of the trapped UH waves and the estimated growth rates, we conduct 1D particle-in-cell simulations in the case of low-temperature plasmas. Lastly, a lower limit to the magnetic field strength is found, where the growth rate of the instability significantly declines.