neoclassical tearing mode
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2022 ◽  
Author(s):  
Tong Liu ◽  
Zheng-Xiong Wang ◽  
Lai Wei ◽  
Jialei Wang

Abstract The explosive burst excited by neoclassical tearing mode (NTM) is one of the possible candidates of disruptive terminations in reversed magnetic shear (RMS) tokamak plasmas. For the purpose of disruption avoidance, numerical investigations have been implemented on the prevention of explosive burst triggered by the ill-advised application of electron cyclotron current drive (ECCD) in RMS configuration. Under the situation of controlling NTMs by ECCD in RMS tokamak plasmas, a threshold in EC driven current has been found. Below the threshold, not only are the NTM islands not effectively suppressed, but also a deleterious explosive burst could be triggered, which might contribute to the major disruption of tokamak plasmas. In order to prevent this ECCD triggering explosive burst, three control strategies have been attempted in this work and two of them have been recognized to be effective. One is to apply differential poloidal plasma rotation in the proximity of outer rational surface during the ECCD control process; The other is to apply two ECCDs to control NTM islands on both rational surfaces at the same time. In the former strategy, the threshold is diminished due to the modification of classical TM index. In the latter strategy, the prevention is accomplished as a consequence of the reduction of the coupling strength between the two rational surfaces via the stabilization of inner islands. Moreover, the physical mechanism behind the excitation of the explosive burst and the control processes by different control strategies have all been discussed in detail.


2022 ◽  
Author(s):  
Andres Pajares ◽  
Eugenio Schuster ◽  
Kathreen E Thome ◽  
Anders S Welander ◽  
Jayson L Barr ◽  
...  

Abstract Simulations using the Control-Oriented Transport SIMulator (COTSIM) and DIII-D experiments have been carried out to demonstrate the performance of a novel integrated-control architecture for simultaneous regulation of individual-scalar magnitudes. The individual scalars considered in this work include kinetic variables, such as the thermal stored-energy or volume-average toroidal rotation, and magnetic variables such as the safety factor profile at different spatial locations. Separate control algorithms have been designed independently for each of these individual variables that use robust, nonlinear control techniques. In addition, the individual-scalar controllers have been integrated with Neoclassical Tearing-Mode (NTM) suppression algorithms, supervisory and exception handling algorithms, and an actuator manager, both within COTSIM and in the Plasma Control System (PCS) of the DIII-D tokamak. The resulting architecture has a high level of integration and some of the functionalities that will be required to fulfill the advanced-control requirements anticipated for ITER. Initial simulations using COTSIM suggest that the plasma performance and its Magneto-HydroDynamic (MHD) stability may be improved under integrated feedback control. These simulation results also show good qualitative agreement with DIII-D experimental results in the steady-state high-$q_{min}$ scenario, which is one of the candidates for steady-state operation in ITER. By means of individual-scalar feedback-control techniques in conjunction with NTM-suppression techniques, the confinement deterioration caused by NTMs in these scenarios may be significantly ameliorated.


2021 ◽  
Author(s):  
Robert John La Haye ◽  
Colin Chrystal ◽  
E J Strait ◽  
James D Callen ◽  
Chris C Hegna ◽  
...  

Author(s):  
Takahiro Bando ◽  
Takuma Wakatsuki ◽  
Mitsuru Honda ◽  
Isayama Akihiko ◽  
Kouji Shinohara ◽  
...  

2021 ◽  
Vol 16 (0) ◽  
pp. 1402030-1402030
Author(s):  
Takahiro BANDO ◽  
Shizuo INOUE ◽  
Kouji SHINOHARA ◽  
Akihiko ISAYAMA ◽  
Takuma WAKATSUKI ◽  
...  

AIP Advances ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 035212
Author(s):  
Zhen Yang ◽  
Bin Wu ◽  
Yuanlai Xie ◽  
Yuqing Chen ◽  
Hongming Zhang ◽  
...  

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
C. Tsironis ◽  
P. Papagiannis ◽  
F. Bairaktaris ◽  
S. I. Valvis ◽  
K. Hizanidis

In this work we study the undesired effects of electron density fluctuations (in the form of blob structures which may exist in the edge region of tokamak plasmas) to the electron-cyclotron wave propagation and current drive in connection to the efficiency of neoclassical tearing mode stabilization. Our model involves the evaluation of the driven current in the presence of density perturbations, by using a combination of a wave solver based on the transfer matrix and electromagnetic homogenization methods for the propagation part prior to and inside the region of these structures (where standard asymptotic propagation methods may not be valid due to the short-wavelength limit breakdown), with a ray tracing code including island geometry effects and current drive computation for the propagation past the perturbed region. The computed driven current is input into the modified Rutherford equation in order to estimate the consequences of the wave deformation (driven by the density fluctuations) to the mode stabilization.


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