Wave-Number Spectral Characteristics of Drift Wave Micro-Turbulence with Large-Scale Structures

Wave-number spectral characteristics of drift wave micro-turbulence with large-scale structures （LSSs） including zonal flows （ZFs） and Kelvin-Holmheltz （KH） mode are investigated based on three dimensional gyrofluid simulations in a slab geometry. The focus is on the property of the wave-number spectral scaling law of the ambient turbulence under the back reaction of the self-generated LSSs. A comparison of the spectral scaling laws between ion/electron temperature gradient （ITG/ETG） driven turbulences is presented. It is shown that the spectral scaling of the ITG turbulence with robust ZFs is fitted well by an exponential-law function （Φ^2/2）E∝e^-λkx in kx and a power-law one in （Φ^2/2）p∝ky^-β in ky. However, the ETG turbulence is characterized by a mixing Kolmogorov-like power-law and exponential-law （Φ^2/2）E∝e-λkx＇yk^-3x,y/（1 ＋ k^2x,y）^2 scaling for both kx and ky spectra due to the ZFs and KH mode dynamics, with λ and β the slope index factors. The underlying physical mechanism is understood as the spectral scattering caused by the back-reaction of the LSSs on the ambient turbulence. These findings may provide helpful guideline to diagnose the plasma fluctuations and flow structures in experiments.

CO_(2) corrosion of X80 steel welded joints under micro-turbulence induced by welding reinforcement height

Corrosion failure accidents owing to flow erosion and pipeline corrosion frequently occur during transportation.The welding reinforcement height(WRH)can induce locally micro-turbulent flow field,which aggravates local corrosion of welded joints.A high wall shear stress(WsS)experimental setup was established to conduct the online electrochemical corrosion test.The influence of WRH sizes on local corrosion of welded joints was studied at different flow rates.The electrochemical signals of the local corrosion of X80 welded joints at different flow rates were monitored in real time using electrochemical impedance spectroscopy and wire beam microelectrode.In addition,the corrosion products composition and properties were analyzed.The results show that the micro-turbulent flow fields induced by the WRHs can enhance ion mass transfer near the welded joints.The corrosion products on the WRH surface also present different microscopic morphologies at different flow rates.In strong flow fields,the locally enhanced wsS can peel off the dense corrosion product partially,leading to the electrochemical distribution of large cathode and small anode,which accelerates the occurrence and development processes of the local corrosion of welded joints.The scientific guidelines for the corrosion protection of long-distance oil and gas pipelines can be potentially provided.

Studies of collisionless shockwaves using high-power laser pulses in laboratories

The remarkable experimental progress in the studies of collisionless shockwave（CS） in laboratories employing highpower lasers is briefly reviewed. The results show that CS can be generated in laser-produced plasmas due to the microturbulence associated with instabilities. CS is one of the most important astronomical phenomena. It has been found in supernova remnants（SNRs）, Sun–Earth space, etc. This paper focuses on CS in ways relevant to SNRs. Laboratory astrophysics（LA）, a new interdisciplinary frontier of astrophysics, plasma and laser physics, has developed rapidly in recent years. As an accessory to the astronomical observation, LA experimenters can closely study some astronomical events scaled-down to controllable phenomena.

Fully Kinetic, Electromagnetic Particle-in-Cell Simulations of Plasma Microturbulence

A novel numerical method,based on physical intuition,for particle-in-cell simulations of electromagnetic plasma microturbulence with fully kinetic ion and electron dynamics is presented.The method is based on the observation that,for lowfrequency modes of interest[ω/ω_(ci)≪1,ωis the typical mode frequency andωci is the ion cyclotron frequency]the impact of particles that have velocities larger than the resonant velocity,v^(r)∼ω/k_(||)(k_(||) is the typical parallel wavenumber)is negligibly small(this is especially true for the electrons).Therefore it is natural to analytically segregate the electron response into an adiabatic response and a nonadiabatic response and to numerically resolve only the latter:this approach is termed the splitting scheme.However,the exact separation between adiabatic and nonadiabatic responses implies that a set of coupled,nonlinear elliptic equations has to be solved;in this paper an iterative technique based on the multigrid method is used to resolve the apparent numerical difficulty.It is shown that the splitting scheme allows for clean,noise-free simulations of electromagnetic drift waves and ion temperature gradient(ITG)modes.It is also shown that the advantage of noise-free kinetic simulations translates into better energy conservation properties.