9:45 AM - 10:00 AM
[PEM16-04] Entropy cascading and structures of distribution function in drift wave turbulence
Keywords:space plasma, turbulence, distribution funciton
High temperature plasmas in space and laboratory are almost collisionless, and the distribution function can be far from the equilibrium state. Fluctuations on the distribution function driven by nonlinear plasma waves or turbulence suffer from filamentation or shearing on the phase space, and the characteristic scale lengths of the perturbed distribution function (delta-f) will be shorter and shorter through the turbulence cascade and the phase mixing until the fine structures are dissipated by collisions. This process plays a key role in the turbulence dissipation or heating in the high temperature plasmas.
In the present work, we consider a drift wave turbulence driven by the ion temperature gradient in a magnetized plasma with weak collisionality. Real and velocity space spectra of the distribution function obtained from the four-dimensional gyrokinetic simulations are investigated by means of the Fourier-Hermite expansions. The entropy variable defined by the L2 norm of delta-f cascades not only in the real wavenumber space, but also in the Hermite spectrum through the ballistic motion of particles. It is noteworthy that fluctuations with high parallel wavenumbers generated in the ExB turbulence induce the fine velocity space structures of delta-f, and that a nearly constant profile of the entropy transfer function is observed with the power-law of the Hermite spectrum of the entropy variable in agreement with a theoretical prediction.
* This work is supported by JSPS KAKENHI Grant Number JP16H04086.
In the present work, we consider a drift wave turbulence driven by the ion temperature gradient in a magnetized plasma with weak collisionality. Real and velocity space spectra of the distribution function obtained from the four-dimensional gyrokinetic simulations are investigated by means of the Fourier-Hermite expansions. The entropy variable defined by the L2 norm of delta-f cascades not only in the real wavenumber space, but also in the Hermite spectrum through the ballistic motion of particles. It is noteworthy that fluctuations with high parallel wavenumbers generated in the ExB turbulence induce the fine velocity space structures of delta-f, and that a nearly constant profile of the entropy transfer function is observed with the power-law of the Hermite spectrum of the entropy variable in agreement with a theoretical prediction.
* This work is supported by JSPS KAKENHI Grant Number JP16H04086.