Kinetic model and Vlasov simulation verification of two-ion decay instability

Area of Science:

• Plasma Physics
• Kinetic Theory
• Wave Phenomena

Background:

• Two-ion decay (TID) is a plasma instability where a pump ion-acoustic wave (IAW) decays into two daughter IAWs.
• Previous fluid theories underestimated the growth rate of this instability.
• Understanding TID is crucial for various plasma applications.

Purpose of the Study:

• To develop a kinetic theory for the longitudinal decay of two-ion decay (TID).
• To accurately predict the instability growth rate and threshold for TID.
• To resolve discrepancies between theoretical predictions and simulation results.

Main Methods:

• Developed a kinetic theory for TID.
• Employed full kinetic Vlasov simulations.
• Utilized hybrid Vlasov simulations (kinetic ions, Boltzmann electrons).

Main Results:

• The kinetic theory provides accurate predictions for TID growth rate and threshold.
• High quantitative agreement was found between theory and simulations for 8≤ZT_{e}/T_{i}≤15.
• The kinetic model corrects the underestimation of growth rates by fluid theory by a factor of 2-3.

Conclusions:

• The developed kinetic theory successfully describes the longitudinal decay of two-ion decay (TID).
• This kinetic approach resolves a long-standing issue with fluid theory's underestimation of growth rates.
• The theory offers explanations for observed TID characteristics, including subharmonic growth rate and wave number dependencies.