Investigations of plasma response associated with Resonant Magnetic Perturbation fields using perturbation method in KSTAR H-mode plasmas

The plasma response associated with the Resonant Magnetic Perturbation (RMP) field was investigated using the small edge perturbations induced by a modulated Supersonic Molecular Beam Injection (SMBI) in KSTAR. The modulated SMBI provides a time-varying perturbation of the plasma density source in the region just inside the last closed flux surface (LCFS) and a modulated flow damping rate. Radial propagation of the toroidal rotation perturbation induced by SMBI from the q=3 surface to the q=2 surface was observed. Theoretical analysis using the General Perturbed Equilibrium Code (GPEC) of the RMP intensity profiles of the RMP field is consistent with the phase profile of the toroidal rotation perturbation.

Radial Sizes and Expansion Behavior of ICMEs in Solar Cycles 23 and 24

We attempt to understand the influence of the heliospheric state on the expansion behavior of coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) in solar cycles 23 and 24. Our study focuses on the distributions of the radial sizes and duration of ICMEs, their sheaths, and magnetic clouds (MCs). We find that the average radial size of ICMEs (MCs) at 1 AU in cycle 24 is decreased by ∼33% (∼24%) of its value in cycle 23. This is unexpected as the reduced total pressure in cycle 24 should have allowed the ICMEs in cycle 24 to expand considerably to larger sizes at 1 AU. To understand this, we study the evolution of radial expansion speeds of CME-MC pairs between the Sun and Earth based on their remote and in situ observations. We find that radial expansion speeds of MCs at 1 AU in solar cycles 23 and 24 are only 9 and 6%, respectively, of their radial propagation speeds. Also, the fraction of radial propagation speeds as expansion speeds of CMEs close to the Sun are not considerably different between solar cycles 23 and 24. We also find a constant (0.63 ± 0.1) dimensionless expansion parameter of MCs at 1 AU for both solar cycles 23 and 24. We suggest that the reduced heliospheric pressure in cycle 24 is compensated by the reduced magnetic content inside CMEs/MCs, which did not allow the CMEs/MCs to expand enough in the later phase of their propagation. Furthermore, the average radial sizes of sheaths are the same in both cycles, which is unexpected, given the weaker CMEs/ICMEs in cycle 24. We discuss the possible causes and consequences of our findings relevant for future studies.

(Non)-radial propagation of the solar wind flow

<p>The solar wind aberration due to non-radial velocity components and the Earth orbital motion is important for the overall magnetosphere geometry because the magnetospheric tail is aligned with the solar wind flow. This paper investigates an evolution of non-radial components of the solar wind flow along the path from the Sun to 6 AU. A comparison of observations at 1 AU and closer to or further from the Sun based on measurements of many spacecraft at different locations in the heliosphere (Wind, ACE, Spektr-R, THEMIS B and C, Helios 1 and 2, Mars-Express, Voyager 1 and 2) shows that (i) the average values of non-radial components vary with the distance from the Sun and (ii) they differ according to solar wind streams.</p>

The quantitative characterization of the ignition process for a lean staged injector: Influence of the air split between pilot swirlers

The ignition of a lean staged injector aimed at aeronautical application is a transient and complex phenomenon, which involves fluid dynamics, turbulent mixing, chemical kinetics, as well as their mutual interactions. In the present research, a staged injector, designed based on stratified partially premixed combustion concept, is introduced. The ignition performance of stratified partially premixed injectors with different air split ratios between pilot swirlers are experimentally acquired, which exhibits apparent distinctions. In order to make quantitative analyses, the classical physical ignition model is improved, in which the flame propagation process is further divided into the axial and radial propagation sub-processes. Nonreacting flow field and discrete phase simulations, validated by experiment results, are utilized to obtain the velocity and spray distributions. Physical parameters characterizing the ignition sub-processes are defined and calculated based on the numerical simulation results. Conclusions are made by comparing the physical parameters of the ignition sub-processes. The radial propagation of the ignition kernel is responsible for the ignition performance difference between the two injectors with different pilot air split ratios (PASR) in that the average equivalence ratio along the radial propagation route of PASR = 7:3 is one order richer than that of PASR = 2:8. The present ignition analysis and model can be further extended and developed for the optimization of ignition performance of lean staged injector.

The Radial Propagation of Heat in Strongly Driven Non-Equilibrium Fusion Plasmas

Heat transport is studied in strongly heated fusion plasmas, far from thermodynamic equilibrium. The radial propagation of perturbations is studied using a technique based on the transfer entropy. Three different magnetic confinement devices are studied, and similar results are obtained. “Minor transport barriers” are detected that tend to form near rational magnetic surfaces, thought to be associated with zonal flows. Occasionally, heat transport “jumps” over these barriers, and this “jumping” behavior seems to increase in intensity when the heating power is raised, suggesting an explanation for the ubiquitous phenomenon of “power degradation” observed in magnetically confined plasmas. Reinterpreting the analysis results in terms of a continuous time random walk, “fast” and “slow” transport channels can be discerned. The cited results can partially be understood in the framework of a resistive Magneto-HydroDynamic model. The picture that emerges shows that plasma self-organization and competing transport mechanisms are essential ingredients for a fuller understanding of heat transport in fusion plasmas.