Alfredo Pironti

Design and experimental testing of a robust multivariable controller on a tokamak

Describes the design and the experimental validation of a multivariable digital controller for a Tokamak, the Tokamak a configuration variable (TCV). The design of the controller is based on a linearized model of the plasma confined in the Tokamak. The plant is multiple-input-multiple-output (MIMO) and the various outputs are strongly coupled. Moreover the plant is open-loop unstable. The scope of the controller is to stabilize the plasma and to guarantee some closed-loop performance in terms of decoupling among the plant outputs. The proposed controller is composed of two nested loops: one is devoted to the vertical stabilization, the other, designed using the /spl Hscr//sub /spl infin// technique, guarantees the control of the plasma current and of the plasma shape. After massive simulations, this controller has been successfully tested on the plant. The experimental results show a significant improvement of the performance with respect to those obtained with a proportional integral derivative (PID) MIMO controller, that was used before on the plant.

Plasma Modelling for Magnetic Control

The aim of this chapter is to derive a linearized mathematical model describing the interaction between the plasma ring and the voltages applied to the poloidal field coils.

Model Based Estimation Of The Eddy Currents For The Iter Tokamak

Eddy currents flowing in the conductive structures surrounding the plasma in a tokamak affect magnetic measurements (magnetic fields and fluxes at given points), which are used to estimate plasma quantities such as plasma toroidal current, position and shape. Due to their spatial distribution and their fast variations, eddy currents are difficult sources to characterize. This is particularly true when magnetic sensors are outside the conductive plasma chamber implying that eddy currents flow between the so-called measurement contour and the plasma region. As a matter of fact many plasma shape identification algorithms assume the plasma current distribution as the only magnetic source located inside the measurement contour. In this paper we deal with the problem of estimating eddy currents in the ITER tokamak by means of a dynamic observer to wash out their contribution to magnetic measurements.

Plasma Shape Control at JET

The controller design described in this chapter has been carried out in the framework of some projects aimed at assessing the possibility of controlling accurately highly elongated plasmas at JET with the existing active circuits and control hardware [95].

Plasma Shape Control for ITER

In this chapter, we show that the configuration of the ITER tokamak enables the design of a low-order controller based on the fact that the vertical position control and the plasma current and shape control can be performed on different time scales.

Plasma Position and Current Control at FTU

In this chapter we present the design of a plasma radial position and current controller for the FTU tokamak. This design is based on a detailed simulation model of the tokamak; exploiting this model-based approach, no experimental tuning of the controller gains has been necessary.

Plasma Magnetic Control Problem

In the previous chapters, we have shown how it is possible to derive an FDLTI (finite-dimension linear time-invariant) model able to describe the interactions between the plasma and the surrounding structures, in terms of specified inputs and outputs, under certain simplifying assumptions.

Modelling of the Resistive Wall Modes

In Sect. 2.4 we have introduced the concept of plasma equilibrium where the magnetic confinement forces produced by the active coils of the tokamak balance the plasma pressure.

The Plasma Boundary and Its Identification

As seen in the previous chapter, the magnetic confinement of the plasma in tokamak machines is obtained via the interaction of the plasma with an external electromagnetic field.

Plasma Shape Control at TCV

A thorough description of the TCV is beyond the scope of this work. The interested reader is referred to [91]. Hereafter, we will outline only those aspects that are relevant to control.