Effects Of Wave Heating Research Articles

Integrated modelling of tungsten accumulation control with wave heating: validation in ASDEX Upgrade and predictions for ITER

Abstract In present-day fusion devices, central wave heating is crucial to avoid core tungsten (W) accumulation. In this work, we present an integrated modelling framework that reproduces the reduction of core W peaking in ASDEX Upgrade experiments when multiple transport channels are self-consistently evolved, emphasizing the effects of wave heating on turbulent and neoclassical W transport. Predictions for the ITER 15 MA baseline are then provided. We show that the core of a reactor is in a different transport regime for W as compared to present-day tokamaks. The challenges introduced by W arise from global radiation losses that can hinder operation in H-mode, instead of local central accumulation.

Hydrodynamic Simulations of Pre-supernova Outbursts in Red Supergiants: Asphericity and Mass Loss

Abstract The activity of a massive star approaching core-collapse can strongly affect the appearance of the star and its subsequent supernova. Late-phase convective nuclear burning generates waves that propagate toward the stellar surface, heating the envelope and potentially triggering mass loss. In this work, we improve on previous one-dimensional models by performing two-dimensional simulations of the pre-supernova mass ejection phase due to deposition of wave energy. Beginning with stellar evolutionary models of a 15 M ⊙ red supergiant star during core O-burning, we treat the rate and duration of energy deposition as model parameters and examine the mass-loss dependence and the pre-explosion morphology accordingly. Unlike one-dimensional models, density inversions due to wave heating are smoothed by Rayleigh–Taylor instabilities, and the primary effect of wave heating is to radially expand the star’s hydrogen envelope. For low heating rates with long durations, the expansion is nearly homologous, whereas high but short-lived heating can generate a shock that drives envelope expansion and results in a qualitatively different density profile at the time of core-collapse. Asymmetries are fairly small, and large amounts of mass loss are unlikely unless the wave heating exceeds expectations. We discuss implications for pre-supernova stellar variability and supernovae light curves.

Wave Heating in Simulated Multistranded Coronal Loops

Abstract It has been found that the Kelvin–Helmholtz instability (KHI) induced by both transverse and torsional oscillations in coronal loops can reinforce the effects of wave heating. In this study, we model a coronal loop as a system of individual strands, and we study wave heating effects by considering a combined transverse and torsional driver at the loop footpoint. We deposit the same energy into the multistranded loop and an equivalent monolithic loop, and then observe a faster increase in the internal energy and temperature in the multistranded model. Therefore, the multistranded model is more efficient in starting the heating process. Moreover, higher temperature is observed near the footpoint in the multistranded loop and near the apex in the monolithic loop. The apparent heating location in the multistranded loop agrees with the previous predictions and observations. Given the differences in the results from our multistranded loop and monolithic loop simulations, and given that coronal loops are suggested to be multistranded on both theoretical and observational grounds, our results suggest that the multistrandedness of coronal loops needs to be incorporated in future wave-based heating mechanisms.

Heating Effects from Driven Transverse and Alfvén Waves in Coronal Loops

Abstract Recent numerical studies revealed that transverse motions of coronal loops can induce the Kelvin–Helmholtz instability (KHI). This process could be important in coronal heating because it leads to dissipation of energy at small spatial scale plasma interactions. Meanwhile, small-amplitude decayless oscillations in coronal loops have been discovered recently in observations of SDO/AIA. We model such oscillations in coronal loops and study wave heating effects, considering a kink and Alfvén driver separately and a mixed driver at the bottom of flux tubes. Both the transverse and Alfvén oscillations can lead to the KHI. Meanwhile, the Alfvén oscillations established in loops will experience phase mixing. Both processes will generate small spatial scale structures, which can help the dissipation of wave energy. Indeed, we observe the increase of internal energy and temperature in loop regions. The heating is more pronounced for the simulation containing the mixed kink and Alfvén driver. This means that the mixed wave modes can lead to a more efficient energy dissipation in the turbulent state of the plasma and that the KHI eddies act as an agent to dissipate energy in other wave modes. Furthermore, we also obtained forward-modeling results using the FoMo code. We obtained forward models that are very similar to the observations of decayless oscillations. Due to the limited resolution of instruments, neither Alfvén modes nor the fine structures are observable. Therefore, this numerical study shows that Alfvén modes probably can coexist with kink modes, leading to enhanced heating.

Pre-supernova outbursts via wave heating in massive stars – II. Hydrogen-poor stars

Pre-supernova (SN) outbursts from massive stars may be driven by hydrodynamical wave energy emerging from the core of the progenitor star during late nuclear burning phases. Here, we examine the effects of wave heating in stars containing little or no hydrogen, i.e., progenitors of type IIb/Ib SNe. Because there is no massive hydrogen envelope, wave energy is thermalized near the stellar surface where the overlying atmospheric mass is small but the optical depth is large. Wave energy can thus unbind this material, driving an optically thick, super-Eddington wind. Using 1D hydodynamic MESA simulations of $\sim \! 5 \, M_\odot$ He stars, we find that wave heating can drive pre-SN outbursts composed of a dense wind whose mass loss rate can exceed $\sim \! 0.1 \, M_\odot/{\rm yr}$. The wind terminal velocities are a few $100 \, {\rm km}/{\rm s}$, and outburst luminosities can reach $\sim \! 10^6 \, L_\odot$. Wave-driven outbursts may be linked with observed or inferred pre-SN outbursts of type Ibn/transitional/transformational SNe, and pre-SN wave-driven mass loss is a good candidate to produce these types of SNe. However, we also show that non-linear wave breaking in the core of the star may prevent such outbursts in stars with thick convective helium-burning shells. Hence, only a limited subset of SN progenitors are likely to experience wave-driven pre-SN outbursts.

Simulations of fully deformed oscillating flux tubes

Context. In recent years, a number of numerical studies have been focusing on the significance of the Kelvin–Helmholtz instability in the dynamics of oscillating coronal loops. This process enhances the transfer of energy into smaller scales, and has been connected with heating of coronal loops, when dissipation mechanisms, such as resistivity, are considered. However, the turbulent layer is expected near the outer regions of the loops. Therefore, the effects of wave heating are expected to be confined to the loop’s external layers, leaving their denser inner parts without a heating mechanism. Aim. In the current work we aim to study the spatial evolution of wave heating effects from a footpoint driven standing kink wave in a coronal loop. Methods. Using the MPI-AMRVAC code, we performed ideal, three dimensional magnetohydrodynamic simulations of footpoint driven transverse oscillations of a cold, straight coronal flux tube, embedded in a hotter environment. We have also constructed forward models for our simulation using the FoMo code. Results. The developed transverse wave induced Kelvin–Helmholtz (TWIKH) rolls expand throughout the tube cross-section, and cover it entirely. This turbulence significantly alters the initial density profile, leading to a fully deformed cross section. As a consequence, the resistive and viscous heating rate both increase over the entire loop cross section. The resistive heating rate takes its maximum values near the footpoints, while the viscous heating rate at the apex. Conclusions. We conclude that even a monoperiodic driver can spread wave heating over the whole loop cross section, potentially providing a heating source in the inner loop region. Despite the loop’s fully deformed structure, forward modelling still shows the structure appearing as a loop.

Heating by transverse waves in simulated coronal loops

Recent numerical studies of oscillating flux tubes have established the significance of resonant absorption in the damping of propagating transverse oscillations in coronal loops. The nonlinear nature of the mechanism has been examined alongside the Kelvin-Helmholtz instability, which is expected to manifest in the resonant layers at the edges of the flux tubes. While these two processes have been hypothesized to heat coronal loops through the dissipation of wave energy into smaller scales, the occurring mixing with the hotter surroundings can potentially hide this effect. We aim to study the effects of wave heating from driven and standing kink waves in a coronal loop. Using the MPI-AMRVAC code, we perform ideal, three dimensional magnetohydrodynamic (MHD) simulations of both (a) footpoint driven and (b) free standing oscillations in a straight coronal flux tube, in the presence of numerical resistivity. We have observed the development of Kelvin-Helmholtz eddies at the loop boundary layer of all three models considered here, as well as an increase of the volume averaged temperature inside the loop. The main heating mechanism in our setups was Ohmic dissipation, as indicated by the higher values for the temperatures and current densities located near the footpoints. The introduction of a temperature gradient between the inner tube and the surrounding plasma, suggests that the mixing of the two regions, in the case of hotter environment, greatly increases the temperature of the tube at the site of the strongest turbulence, beyond the contribution of the aforementioned wave heating mechanism.

The surf zone heat budget: The effect of wave heating

AbstractSurf zone incident wave energy flux is dissipated by wave breaking which through viscosity generates heat. This effect is not present in shelf heat budgets and has not previously been considered. Pier‐based observations of water temperature in 1–4 m depth, meteorology, and waves are used to test a surf zone heat budget, which closes on diurnal and longer time scales. Wave energy flux is the second most variable term with mean contribution one fourth of the mean short‐wave radiation. The heat budget residual has semidiurnal and higher‐frequency variability and net cooling. Cross‐shore advective heat flux driven by internal wave events, rip currents, and undertow contribute to this residual variability and net cooling. In locations with large waves, steeper beaches, or less solar radiation, the ratio of wave energy flux to short‐wave radiation may be >1.

Acceleration and heating of two-fluid solar wind by Alfven waves

view Abstract Citations (17) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Acceleration and Heating of Two-Fluid Solar Wind by Alfven Waves Sandbaek, Ornulf ; Leer, Egil Abstract Earlier model studies of solar wind driven by thermal pressure and Alfven waves have shown that wave amplitudes of 20-30 km/s at the coronal base are sufficient to accelerate the flow to the high speeds observed in quasi-steady streams emanating from large coronal holes. We focus on the energy balance in the proton gas and show that heat conduction from the region where the waves are dissipated may play an important role in determining the proton temperature at the orbit of Earth. In models with 'classical' heat conduction we find a correlation between high flow speed, high proton temperature, and low electron temperature at 1 AU. The effect of wave heating on the development of anisotropies in the solar wind proton gas pressure is also investigated in this study. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173828 Bibcode: 1994ApJ...423..500S Keywords: Energy Transfer; Magnetohydrodynamic Waves; Solar Corona; Solar Wind; Two Fluid Models; Electron Energy; Plasma Acceleration; Plasma Heating; Thermal Conductivity; Astrophysics; SUN: CORONA; SUN: SOLAR WIND full text sources ADS |