The decadally modulating eddy field in the upstream Kuroshio Extension and its related mechanisms

Both the level of the high-frequency eddy kinetic energy（HF-EKE） and the energy-containing scale in the upstream Kuroshio Extension（KE） undergo a well-defined decadal modulation, which correlates well with the decadal KE path variability. The HF-EKE level and the energy-containing scales will increase with unstable KE path and decrease with stable KE path. Also the mesoscale eddies are a little meridionally elongated in the stable state, while they are much zonally elongated in the unstable state. The local baroclinic instability and the barotropic instability associated with the decadal modulation of HF-EKE have been investigated. The results show that the baroclinic instability is stronger in the stable state than that in the unstable state, with a shorter characteristic temporal scale and a larger characteristic spatial scale. Meanwhile, the regional-averaged barotropic conversion rate is larger in the unstable state than that in the stable state. The results also demonstrate that the baroclinic instability is not the dominant mechanism influencing the decadal modulation of the mesoscale eddy field, while the barotropic instability makes a positive contribution to the decadal modulation.

Weibel Instability Growth Rate in Magnetized Plasmas with Quasi-Relativistic Distribution Function

The mechanism of the Weibel instability is investigated for dense magnetized plasmas. As we know, due to the electron velocity distribution, the Coulomb collision effect of electron-ion and the relativistic properties play an important role in such study. In this study an analytical expression for the growth rate and the condition of restricting the Weibel instability are derived for low-frequency limit. These calculations are done for the oscillation frequency dependence on the electron cyclotron frequency. It is shown that, the relativistic properties of the particle lead to increasing the growth rate of the instability. On the other hand the collision effects and background magnetic field try to decrease the growth rate by decreasing the temperature anisotropy and restricting the particles movement.

Study of Robinson instabilities with a higher-harmonic cavity for the HLS phase Ⅱ project

In the Phase Ⅱ Project at the Hefei Light Source, a fourth-harmonic ＂Landau＂ cavity will be operated in order to suppress the coupled-bunch instabilities and increase the beam lifetime of the Hefei storage ring. Instabilities limit the utility of the higher-harmonic cavity when the storage ring is operated with a small momentum compaction. Analytical modeling and simulations show that the instabilities result from Robinson mode coupling. In the analytic modeling, we operate an algorithm to consider the Robinson instabilities. To study the evolution of unstable behavior, simulations have been performed in which macroparticles are distributed among the buckets. Both the analytic modeling and simulations agree for passive operation of the harmonic cavity.