Nonlinear control of the minimum safety factor in tokamaks by optimal allocation of spatially moving electron cyclotron current drive

IF 1.9 3区 工程技术 Q1 NUCLEAR SCIENCE & TECHNOLOGY
Sai Tej Paruchuri , Andres Pajares , Tariq Rafiq , Eugenio Schuster
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Abstract

The minimum value of the safety factor profile is related to the magnetohydrodynamic (MHD) stability of the plasma confined in a tokamak. Therefore, active control of the minimum safety factor may mitigate MHD instabilities that can degrade or even terminate plasma confinement. Typically, in most tokamak scenarios, the minimum safety factor evolves spatially with time, i.e., the location at which the safety factor achieves the minimum value changes with time. In addition to the inherent nonlinearities in the minimum safety factor evolution, its spatial variation makes the control design challenging. In particular, complexity in control design may arise from the need for time-dependent nonlinear models that account for spatial variation of the minimum safety factor. Furthermore, the minimum safety factor may drift to locations where the actuator authority is low. The problem of minimum safety factor control with target location tracking and moving electron cyclotron current drive (ECCD) is addressed in this work. A nonlinear time-dependent model that incorporates the spatial variation of the minimum safety factor is presented. A nonlinear controller based on optimal feedback linearization is developed to track a target minimum safety factor. The proposed controller treats the ECCD position as a controllable variable. In other words, the controller prescribes the ECCD position (in addition to the non-inductive powers) in real time based on an optimal criterion that is defined a priori. This work also presents the steps necessary to integrate the minimum safety factor controller with a total energy controller to achieve multiple control objectives simultaneously. The proposed integrated control algorithm is tested using nonlinear simulations in the Control Oriented Transport SIMulator (COTSIM) for a DIII-D tokamak scenario.

通过优化分配空间移动电子回旋加速器电流驱动,对托卡马克中的最低安全系数进行非线性控制
安全系数曲线的最小值与托卡马克中封闭等离子体的磁流体动力学(MHD)稳定性有关。因此,对最小安全系数的主动控制可减轻 MHD 不稳定性,从而降低甚至终止等离子体约束。通常情况下,在大多数托卡马克方案中,最小安全系数会随时间发生空间变化,即安全系数达到最小值的位置会随时间发生变化。除了最小安全系数演变过程中固有的非线性因素外,其空间变化也给控制设计带来了挑战。特别是,控制设计的复杂性可能来自于需要考虑最小安全系数空间变化的随时间变化的非线性模型。此外,最小安全系数可能会漂移到执行器权限较低的位置。本研究解决了目标位置跟踪和移动电子回旋电流驱动器(ECCD)的最小安全系数控制问题。本文提出了一个包含最小安全系数空间变化的非线性时变模型。基于最优反馈线性化开发的非线性控制器可跟踪目标最小安全系数。所提出的控制器将 ECCD 位置视为可控变量。换句话说,控制器根据事先定义的最优标准,实时规定 ECCD 的位置(以及非感应功率)。这项工作还介绍了将最小安全系数控制器与总能量控制器集成以同时实现多个控制目标的必要步骤。针对 DIII-D 托卡马克方案,在面向控制的传输模拟器(COTSIM)中使用非线性模拟对所提出的集成控制算法进行了测试。
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来源期刊
Fusion Engineering and Design
Fusion Engineering and Design 工程技术-核科学技术
CiteScore
3.50
自引率
23.50%
发文量
275
审稿时长
3.8 months
期刊介绍: The journal accepts papers about experiments (both plasma and technology), theory, models, methods, and designs in areas relating to technology, engineering, and applied science aspects of magnetic and inertial fusion energy. Specific areas of interest include: MFE and IFE design studies for experiments and reactors; fusion nuclear technologies and materials, including blankets and shields; analysis of reactor plasmas; plasma heating, fuelling, and vacuum systems; drivers, targets, and special technologies for IFE, controls and diagnostics; fuel cycle analysis and tritium reprocessing and handling; operations and remote maintenance of reactors; safety, decommissioning, and waste management; economic and environmental analysis of components and systems.
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