Search

Diverse disruption mitigation strategies based on massive material injection have been developed in recent decades, aiming to uniformly deplete the thermal energy stored within plasmas during the thermal quench (TQ) while simultaneously elevating electron density to facilitate runaway electron suppression. Irrespective of the detailed dynamics of the material delivery scheme, deposition location and subsequent density mixing are pivotal in achieving highly efficient mitigation, however, which are markedly influenced by magnetohydrodynamic (MHD) activities. In order to assess the influence of MHD-induced transport on disruption mitigation, a simulation of TQ triggered by pure deuterium (D) deposition is conducted using a three-dimensional (3D) nonlinear reduced MHD code, JOREK. Steady density sources (the deposition rate of 1024 D atoms per second is greater than in real experiments) are introduced at various locations to explore the dynamics. The findings distinctly reveal two types of TQ processes, contingent on locations of deposition (LoD) of the neutral D source. Evidently, the results underscore the effectiveness of proper density mixing and moderated MHD in disruption mitigation. Nonlinear mode coupling emerges as a significant factor in shaping the final outcomes of TQ. Specifically, the 5/2 mode contributes to edge collapse, whereas the 3/2 mode is instrumental in core collapse. Additionally, the investigation indicates that the rise in core density is contingent on LoD, exhibiting threshold behavior. This threshold is observed within the q = 2/1 surface of equilibria, and a rapid increase in core density is witnessed when the density source crosses this threshold. The outcomes point toward the important role of E × B convection due to the 1/1 mode evolution in the process. [ABSTRACT FROM AUTHOR]

Avoiding the major disruption is of paramount importance in future reactor-level devices, for which understanding the disruption mechanism is essential. In this work, MHD instabilities and related dynamic interactions during the major disruption have been investigated in the ohmically heated plasmas in the HL-2A tokamak. It is reported that the interaction between a kind of edge-oscillating-mode (EOM) perturbation and a rotating m/n = 2/1 tearing mode (TM) inside the plasma plays an important role in inducing the mode locking and the subsequent disruption. The EOM perturbation is oscillating in the laboratory frame, which is proposed to be originally generated by the penetrated error field at the plasma edge and is modulated by the rotating 2/1 TM mode. Before mode locking, the 2D electron cyclotron emission imaging shows that the momentary coupling of the EOM and the 2/1 mode can be decoupled each other and the mode structure does not alter significantly. After the mode locking, the EOM and the 2/1 mode expand and couple each other and induce the heat transfer from the core to the edge. The influence of the TM instability and the EOM perturbation on surrounding plasmas prior to the mode locking has also been presented. The results deepen our understanding of the disruption dynamics related to the external field perturbations, especially in the presence of TMs inside the plasma. [ABSTRACT FROM AUTHOR]

Features of fishbone-like trapped energetic electrons driven modes (TEEMs), which are a particular manifestation of the fishbone gap modes, are investigated taking into account model radial profile and the pitch angle distribution of the energetic electrons (EEs). The TEEMs are found unstable only when the beta values of EEs βh (¼pressure of the energetic electrons/pressure of magnetic field) are higher than certain critical values which are proportional to perturbed energy δWc of background plasma and much lower than that for traditional fishbone modes. In addition, TEEMs become stable again and enter a second stable regime whenβh values are higher than second critical values. Furthermore, the modes can only be excited in plasmas which are stable for MHD instabilities. The real frequency and growth rate of the modes are approximately linear and parabolic functions of βh, respectively. The real frequency is very low but not zero in the vicinity of lower beta region, whereas it is comparable to the toroidal precession frequency of the EEs in higher critical beta region. The numerical results show that the second stable regime is easy to form when q=1 flux surface is close to the magnetic axis. Suitable density gradient of EEs and magnetic shear are other two necessary conditions for excitation of the TEEMs. [ABSTRACT FROM AUTHOR]

A non-perturbative magnetohydrodynamic-kinetic hybrid formulation is developed and implemented into the MARS-K code [Liu et al., Phys. Plasmas 15, 112503 (2008)] that takes into account the anisotropy and asymmetry [Graves et al., Nature Commun. 3, 624 (2012)] of the equilibrium distribution of energetic particles (EPs) in particle pitch angle space, as well as first order finite orbit width (FOW) corrections for both passing and trapped EPs. Anisotropic models, which affect both the adiabatic and non-adiabatic drift kinetic energy contributions, are implemented for both neutral beam injection and ion cyclotron resonant heating induced EPs. The first order FOW correction does not contribute to the precessional drift resonance of trapped particles, but generally remains finite for the bounce and transit resonance contributions, as well as for the adiabatic contributions from asymmetrically distributed passing particles. Numerical results for a 9MA steady state ITER plasma suggest that (i) both the anisotropy and FOW effects can be important for the resistive wall mode stability in ITER plasmas; and (ii) the non-perturbative approach predicts less kinetic stabilization of the mode, than the perturbative approach, in the presence of anisotropy and FOW effects for the EPs. The latter may partially be related to the modification of the eigenfunction of the mode by the drift kinetic effects. [ABSTRACT FROM AUTHOR]

Objective: To explore the relationship between coronary tortuosity and coronary microvascular disease (CMVD). Methods: Patients with typical angina symptoms and without serious coronary artery stenosis by coronary angiography were enrolled from June 2014 to December 2016, and CMVD was diagnosed by single photon emission tomography (SPECT). According to the SPECT results, patients were divided to the CMVD group and non-CMVD group. The baseline clinical characteristics, results of coronary angiography were compared between the two groups. The logistic analysis was used to analyze the relationship between coronary tortuosity and CMVD. Result: A total of 117 cases were enrolled, with 69 cases in the CMVD group and 48 cases in the non-CMVD group. No differences were found in gender distribution, age, hypertension, lipid abnormality, hyperuricemia and uses of statins between the two groups (all P >0.05). Incidence of diabetes (78.26%(54/69) vs. 35.42% (17/48) , P <0.05), hs-CRP ((4.29±2.15)mmol/L vs. (2.63±1.20)mmol/L, P <0.001), LDL-C ((2.98±0.96)mmol/L vs. (2.52±0.83)mmol/L, P= 0.008) and homocysteine ((13.7±5.61)mmol/L vs. (11.5±4.38)mmol/L, P= 0.025) levels were higher in the CMVD group than in the non-CMVD group. The data derived from echocardiographic examination were similar between the two groups. The Corrected TIMI frame counts were higher in the CMVD group than in non-CMVD group (LAD: 31.56±4.92 vs. 27.31±3.75, LCX: 29.47±4.18 vs. 26.62±3.19, RCA: 29.09±5.05 vs. 26.24±3.28, all P <0.001). The incidences of coronary atherosclerosis (76.81% (53/69) vs. 27.08% (13/48) , P <0.001) and coronary tortuosity ( (60.87% (42/69) vs. 33.33% (16/48) , P= 0.035) were also higher in the CMVD group than in non-CMVD group. Logistic analysis found that coronary tortuosity ( OR= 6.111, 95% CI 2.707-13.794, P <0.001), diabetes ( OR= 6.565, 95% CI 2.883-14.948, P <0.001) and coronary atherosclerosis ( OR= 8.918, 95% CI 3.822-20.808, P <0.001) were independent risk factors of CMVD. Conclusion: Coronary tortuosity, diabetes and coronary atherosclerosis are related to CMVD in this patient cohort.