Alfvén eigenmodes and other magnetohydrodynamic phenomena have been studied in tokamak plasmas at the Joint European Torus (JET) using a new eight-channel, 4 s, 1 MHz, 12-bit data acquisition system (KC1F) in conjunction with the JET fast Mirnov magnetic fluctuation pickup coils. To this end, the JET magnetic pickup coils were calibrated in the range 30–460 kHz using a new remote calibration technique which accounts for the presence of the first few LRC circuit resonances. Signal processing software has been developed to implement the calibration via digital filtering. A data analysis program has been written which produces spectrograms of fluctuation amplitude and toroidal mode number versus frequency and time, both interactively and for automatic overnight analyses. Modes with amplitudes δB/B⩾10−8 and toroidal mode numbers |n|<32 are now routinely detected. Since KC1F data are now available for over 4000 JET discharges, a pulse-characterization database has been developed to help select pulses of interest for detailed analysis.

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A lumped parameter, state space model for the tokamak transformer including the slow flux penetration in the plasma (skin effect transformer model) is presented. The model does not require detailed or explicit information about plasma profiles or geometry. Instead, this information is lumped in system variables, parameters and inputs. The model has an exact mathematical structure built from energy and flux conservation theorems, predicting the evolution and non linear interaction of the plasma current and internal inductance as functions of the primary coil currents, plasma resistance, non-inductive current drive and the loop voltage at an specific location inside the plasma (equilibrium loop voltage). Loop voltage profile in the plasma is substituted by a three-point discretization, and ordinary differential equations are used to predict the equilibrium loop voltage as function of the boundary and resistive loop voltages. This provides a model for equilibrium loop voltage evolution, which is reminiscent of the skin effect. The order and parameters of this differential equation are determined empirically using system identification techniques. Fast plasma current modulation experiments with Random Binary Signals (RBS) have been conducted in the TCV tokamak to generate the required data for the analysis. Plasma current was modulated in Ohmic conditions between 200kA and 300kA with 30ms rise time, several times faster than its time constant L/R≈200ms. A second order linear differential equation for the equilibrium loop voltage is sufficient to describe the plasma current and internal inductance modulation with 70% and 38% fit parameters respectively. The model explains the most salient features of the plasma current transients, such as the inverse correlation between plasma current ramp rates and internal inductance changes, without requiring detailed or explicit information about resistivity profiles. This proves that lumped parameter modeling approach can be used to predict the time evolution of bulk plasma properties such as plasma inductance or current with reasonable accuracy; at least in Ohmic conditions without external heating and current drive sources.

This paper r e v i w s the experimental status and recevt advances i n AlfvCn Wave Heating (AWH). We discuss the underlying physics of Alfven Wave Heating, as seen by the experiments. The use of AlfvCn Waves for plasna diagnosis is discussed. The results of plasna heating on TCA are s m a r i z e d . Apparent changes i n the current profile are inferred, caused by changes i n the evolving AlfvCn wave spectrun excited. The implications for AWH on larger devices are mentioned. KFrwoRDsAlfven Wave Heating; Tokamak; Kinetic Alfvgn Wave; Profile Cor?trol; Antema Systen; plasm Diagnostics; Tc9. IMTR3DilCTIONI n t h i s paper we shall review the recent experiwntal results obtained i n AlfvCn Wave Heating (AXH). The early experimental results have already been reviewed by Shohet (1978), and w shall not repeat that survey. An overview of the extensive theoretical mrk i n Lhis freqency range is beyond t h i s paper, and the current status has been very recently reviewed by Pppert and colleagues (1586). W e shall review the theoretical basis of .MX frm. the viewpint of the experimental observations made, and shall, i n f a c t , discover that mst of the imprtant concepts manifest themselves i n the results.

Plasma stability is one of the obstacles in the path to the successful operation of fusion devices. Numerical control-oriented codes as it is the case of the widely accepted RZIp may be used within Tokamak simulations. The novelty of this article relies in the hierarchical development of a dynamic control loop. It is based on a current profile Model Predictive Control (MPC) algorithm within a multiloop structure, where a MPC is developed at each step so as to improve the Proportional Integral Derivative (PID) global scheme. The inner control loop is composed of a PID-based controller that acts over the Multiple Input Multiple Output (MIMO) system resulting from the RZIp plasma model of the Tokamak à Configuration Variable (TCV). The coefficients of this PID controller are initially tuned using an eigenmode reduction over the passive structure model. The control action corresponding to the state of interest is then optimized in the outer MPC loop. For the sake of comparison, both the traditionally used PID global controller as well as the multiloop enhanced MPC are applied to the same TCV shot. The results show that the proposed control algorithm presents a superior performance over the conventional PID algorithm in terms of convergence. Furthermore, this enhanced MPC algorithm contributes to extend the discharge length and to overcome the limited power availability restrictions that hinder the performance of advanced tokamaks.