Characteristics Of Localized Modes Research Articles

Elastic wave propagation in one-dimensional phononic crystal with defects

The possibilities of manipulating the behavior of propagating waves using only the appropriate choice of materials is a field of interest in engineering. Phononic Crystals (PnCs) come precisely as a proposal for a device to work with waves, defined as artificial materials obtained from a periodic arrangement of unit cells. This configuration can provide frequency bands where waves cannot propagate (bandgaps). However, this property can be directly influenced by the break in the periodicity pattern of the structure when geometric and/or material parameters are changed in a single part of the unit cell. New propagating modes appear inside the bandgaps, presenting characteristics of localized modes. Different length and diameter combinations are applied to establish the defective cell and verify the existence of defect modes that reveal the degree of influence on the creation of these new modes within the bandgap region. Spectral Element (SEM) and Finite Element (FE) methods are adopted to model the PnCs analysis and the frequency response functions (FRFs). The initial results show that the PnCs with geometric defects have an expressive sensitivity to variations in geometric parameters, mainly variations in the length of the defective cell. A break in periodicity in terms of material will also be performed.

Edge localized mode characteristics and divertor heat flux during stationary and transient phase for CFETR hybrid scenario

The study of edge localized mode (ELM) behavior, stationary heat flux and transient heat flux during the ELM crash phase is performed for a China Fusion Engineering Test Reactor (CFETR) 1 GW hybrid mode operation scenario ( = 7.2 m, = 6.5 T, = 13.78 MA). Modeling and simulation start with a scenario obtained by multi-code integrated modeling on the one modeling framework for integrated tasks framework. Linear stability and nonlinear simulations of ELM dynamics are carried out using the BOUT++ six-field reduced magnetohydrodynamic module, which show a much smaller ELM energy loss (ΔELM ~ 0.13%) compared to that of a Type-I ELM. Parametric analysis of the weak linear growth rate and small ELM energy loss characteristics shed light on physics corresponding to a grassy ELM regime for CFETR 1 GW hybrid scenario. The transient heat flux on the divertor target during this small ELM phase is investigated using BOUT++. We found that upstream radial transport in the scrape-off-layer (SOL) induced by small ELMs is weak, which keeps it in the drift-dominated region. However, the heat flux width is still broadened to = 4.64 mm by the increase of separatrix temperature during ELM nonlinear evolution. The impact of transient peak heat load and ELM energy fluence on tungsten melting and net erosion rate of divertor target is evaluated for the first-time using physics-based transport that connects the pedestal with the SOL. Energy fluence caused by a single ELM pulse is below the tungsten melting limit, while tungsten erosion would exceed the material requirements. We conclude that external mitigation methods, such as divertor detachment and advanced divertor geometry are likely needed for the steady state operation of CFETR.

Localized modes in optics of photonic liquid crystals with local anisotropy of absorption

Recently, there has been much activity in the field of localized optical modes, in particular, edge modes (EM) and defect modes (DM) in chiral liquid crystals (CLCs), mainly due to the possibilities for reaching a low lasing threshold for mirrorless distributed feedback (DFB) lasing in CLCs. In the present chapter, we study theoretically the influence of local absorption anisotropy on the characteristics of localized modes. We present analytical solutions for the EMs and DMs (associated with a local absorption anisotropy in CLCs) and consider some limiting cases simplifying the problem [15].

High Confinement Mode and Edge Localized Mode Characteristics in a Near-Unity Aspect Ratio Tokamak.

Tokamak experiments at near-unity aspect ratio A≲1.2 offer new insights into the self-organized H-mode plasma confinement regime. In contrast to conventional A∼3 plasmas, the L-H power threshold P_{LH} is ∼15× higher than scaling predictions, and it is insensitive to magnetic topology, consistent with modeling. Edge localized mode (ELM) instabilities shift to lower toroidal mode numbers as A decreases. These ultralow-A operations enable heretofore inaccessible J_{edge}(R,t) measurements through an ELM that show a complex multimodal collapse and the ejection of a current-carrying filament.

Edge localized mode characteristics during edge localized mode mitigation by supersonic molecular beam injection in Korea Superconducting Tokamak Advanced Research

It has been reported that supersonic molecular beam injection (SMBI) is an effective means of edge localized mode (ELM) mitigation. This paper newly reports the changes in the ELM, plasma profiles, and fluctuation characteristics during ELM mitigation by SMBI in Korea Superconducting Tokamak Advanced Research. During the mitigated ELM phase, the ELM frequency increased by a factor of 2–3 and the ELM size, which was estimated from the Dα amplitude, the fractional changes in the plasma-stored energy and the line-averaged electron density, and divertor heat flux during an ELM burst, decreased by a factor of 0.34–0.43. Reductions in the electron and ion temperatures rather than in the electron density were observed during the mitigated ELM phase. In the natural ELM phase, frequency chirping of the plasma fluctuations was observed before the ELM bursts; however, the ELM bursts occurred without changes in the plasma fluctuation frequency in the mitigated ELM phase.

Pedestal and edge localized mode characteristics with different first wall materials and nitrogen seeding in ASDEX Upgrade

A comparison of ASDEX Upgrade (AUG) discharges performed with carbon and the full tungsten wall shows that the pedestal performance at low triangularity is not altered without gas puffing. The pedestal electron pressure is the same for both wall materials as is the confinement. With the tungsten wall the natural density is higher even without an additional gas puff. In typical operation with gas puffing the density is again higher in tungsten. This results in a higher collisionality with the tungsten wall. Pedestal pressure and plasma confinement, however, are not degraded until very large amounts of deuterium are puffed.The edge localized mode (ELM) crash in typical AUG discharges is observed to be composed of two independent phases. This is observed for both the carbon and the tungsten wall. The 1st phase of the crash is unaffected by scans of the plasma parameters as long as the pedestal pressure remains constant. The duration of the 2nd phase is strongly anti-correlated with the separatrix density and can be suppressed by the application of nitrogen seeding for divertor cooling. A consistent explanation for the two phases of the ELM crash does not seem possible when considering only the pre-ELM pedestal profiles. The scrape off layer (SOL) plasma provides the necessary free parameter for a consistent explanation, indicating the importance of the SOL in understanding the ELM crash evolution.

Characteristics of the localized modes in 2D phononic crystal with heterostructure point defect

A heterostructure point defect is constructed based on replacing one circular scatter cylinder with one square scatter cylinder in two-dimensional square arrays of circular aluminum cylinders embedded in an air host. Its localized mode characteristics have been studied by using the plane-wave expansion method in combination with a supercell technique and the sonic pressure distribution of the localized modes is also calculated. The results indicate that the localized modes of the heterostructure point defect appear in the gap. The position and number of the localized modes changes with the rotation and filling fraction of the heterostructure point defect. The pressure distribution of localized modes is decided by its position in the gap. The characteristics controlling the localized modes, based on changing the angle and size of the heterostructure point defect, are expected to have broad applications in directional sonic filters and narrow band sonic waveguides.