Dynamic transport characteristics of side-coupled double-quantum-impurity systems

A systematic study is performed on time-dependent dynamic transport characteristics of a side-coupled double-quantum-impurity system based on the hierarchical equations of motion.It is found that the transport current behaves like a single quantum dot when the coupling strength is low during tunneling or Coulomb coupling.For the case of only tunneling transition,the dynamic current oscillates due to the temporal coherence of the electron tunneling device.The oscillation frequency of the transport current is related to the step voltage applied by the lead,while temperature T,electron-electron interaction U and the bandwidth W have little influence.The amplitude of the current oscillation exists in positive correlation with W and negative correlation with U.With the increase in coupling t_(12) between impurities,the ground state of the system changes from a Kondo singlet of one impurity to a spin singlet of two impurities.Moreover,lowering the temperature could promote the Kondo effect to intensify the oscillation of the dynamic current.When only the Coulomb transition is coupled,it is found that the two split-off Hubbard peaks move upward and have different interference effects on the Kondo peak at the Fermi surface with the increase in U_(12),from the dynamics point of view.

Plasma Flows within the Context of Biasing Experiments

The understanding and reduction of turbulent transport in magneticconfinement devices is not only an academic task, but also the matter of practical interest, sincehigh confinement is chosen as the regime for ITER and possible future reactors it reduces both thesize and the cost. Since the pioneering work on CCT a lot of work has been devoted to the effect ofelectric field biasing carried out on many tokamaks, which in general leads to a strongly varyingradial electric fields as a function of radius and a resulting sheared E x B flow, giving rise toimproved confinement properties. The issue of plasma flows is utterly fundamental for understandingof tokamaks aimed at the achievement of fusion energy. This appears in the well known neoclassicaltheory as the most accomplished and self-consistent basis for understanding of fusion plasmas. Itpertains to the novel concept of 'zonal flows' emerging from the recent development of gyro-kinetictransport codes. The poloidal and toroidal flows are also crucial for the concept of the electricfield shear suppression of plasma turbulence in tokamaks. Yet, this timely and topical issue hasremained largely unaddressed experimentally because of great difficulties of measuring flows inplasmas. Recently, the team of scientists from all over the world developed innovative configurationof probes yielding the flow velocity locally. This timely and topical diagnostics has beensuccessfully applied on many tokamaks ranging from the huge JET through medium TEXTOR to a smallCASTOR due to the excellent collaboration and coordination between research teams. Results causedlarge interest of fusion community born out by numerous invited talks delivered at the majorinternational meetings.