Digital Control System for Vertical Stability of the TCV Plasma

In advanced mode operation of fusion devices, real time control plays a central role in achieving the desired plasma performance and minimizing the risk of disruptions. With the advances in digital technologies like Digital Signal Processors (DSPs), Field Programmable Gate Arrays (FPGAs) and standard commercial computer processors, the development of digital control systems to use in fusion experiments has spread to all modern tokamaks. Tokamak à Configuration Variable (TCV) had limited control capabilities due to the utilization of an analogue control system. In the first part of the PhD Program an Advanced Plasma Control System (APCS), capable of improving the capacity of control of highly configurable plasma shapes, position, current and density by the introduction of nonlinear digital controllers, was designed, implemented and integrated in TCV. Early tokamaks with circular cross-section plasmas were not prone to the vertical plasma column instability, an inherent problem arising in plasmas with vertically elongated cross sections, with benefits to the energy confinement time, increased plasma current and beta. To overcome this problem, complex closed feedback loop control systems with a vertical position measurement, signal processing, control algorithm, power supplies and active actuating coils are used. In the second part of the PhD Program a predictive vertical stabilization non-linear digital controller was designed and implemented, with the help of a new mathematical simulator based on a rigid plasma model. The layout of a method to define controllable limits for the plasma position and velocity may be used for the design of new control systems. Evidence is presented of the TCV vertical stability enhancement using the implemented controller during experimental tokamak discharges.