The linear regime of the two-plasmon decay instability in inhomogeneous plasmas

A linear fluid code solving the equations for the two-plasmon decay (TPD) instability has been developed and used to study the TPD instability. Both absolute and convective modes are observed in the simulations using this code, which show that the absolute modes are located close to the quarter-critical-density surface while the convective modes are located in the lower-density region. The maximum growth rates of the absolute modes measured in the simulations agree well with the theoretical results in the limits of large and small values of the parameter β∝Te2/(Iλ2), where Te is the electron temperature, I is the laser intensity, and λ is the laser wavelength. The simulation results also agree with the β-dependent threshold for absolute TPD. A derivation of the convective gain that retains the dependence on electron temperature and perpendicular mode number is presented and it is in good agreement with the simulation results.