ABSTRACT The increasing importance of providing reliable polarimetric measurements in real time, ... more ABSTRACT The increasing importance of providing reliable polarimetric measurements in real time, for both machine protection and plasma control, has motivated the development of a quick version of the calibration algorithms for JET polarimeter. This new code, which interprets the calibration procedure performed before each shot, is based on a physical equivalent model of the diagnostic optical path and is valid for any operational regime of JET. It provides results before the plasma breakdown, and, with its estimates of the optical paths parameters, the polarimetric measurements have an accuracy more than sufficient for real-time purposes. New approximate equations have been validated in order to obtain the line integrated density from the newly calibrated horizontal chords, so that also these polarimetric measurements can also be used for density feedback and machine protection. The availability of reliable polarimetric measurements in real time opens new perspectives also to the determination of the plasma boundary, the magnetic equilibrium, and their use in advanced feedback control schemes.
ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic... more ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic reconstructions in the interior of the plasma column in Tokamaks. In the last years, polarimetry has been increasingly used to provide global constraints to equilibrium codes. Joint European Torus (JET) polarimeter has four lateral channels, whose arrangement is similar to the topology of the diagnostic foreseen in ITER. A statistical analysis of JET polarimetry measurements have been provided in the past for only one vertical channel (CH3) using a polarimetry propagation code based on the Stokes vector formalism. A new propagation code has therefore been developed for the lateral channels to simulate and interpret the measurements of the Faraday rotation (FR) and Cotton-Mouton (CM) phase shift in JET. In this paper, a complete analysis of the integral form of the Stokes equation for the lateral channels is presented. In particular, the analysis shows that there is a strong interaction between the FR and CM effect even at low currents and low magnetic fields. The code results of both FR and CM have been used to estimate the line-integrated density and a proper benchmarking with experimental data has been performed. Two approximations to obtain the electron density in real time, using only plasma current in case of FR measurements and also toroidal magnetic fields in case of CM measurements, are proposed.
ABSTRACT. Real-time simultaneous control of several radially distributed magnetic and kinetic pla... more ABSTRACT. Real-time simultaneous control of several radially distributed magnetic and kinetic plasma parameters (such as the safety factor, q (x), and gyro-normalized temperature gradient, ρTe*(x), respectively) is being investigated on JET, in view of developing integrated control of advanced tokamak scenarios and internal transport barriers suitable for ITER. This paper describes the new model-based optimal profile controller which has been tested during the last experimental campaign. The controller aims to use the combination ...
ABSTRACT Recently a complete model of JET polarimeter calibration has been developed. A specific ... more ABSTRACT Recently a complete model of JET polarimeter calibration has been developed. A specific propagation code has also been written to simulate the measurements of both the vertical and horizontal chords during plasma operation. In this paper, these two models have been checked with residual analysis methods valid for nonlinear systems. The differences between the estimates of the codes and the experimental measurements, during both calibration and plasma operation, have been calculated and analysed statistically. The distribution of the residuals confirms the quality of the model developed to interpret the calibration of the diagnostic. On the other hand, during plasma operation, the residuals do not present a Gaussian distribution and there is clear evidence of serial correlation at subsequent times. Correlation analysis with the inputs indicates that problems with the magnetic field topology, provided by an independent equilibrium code, are the source of the inadequacies in the results of the propagation model.
ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic... more ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic reconstructions in the interior of the plasma column in Tokamaks. In the last years, polarimetry has been increasingly used to provide global constraints to equilibrium codes. Joint European Torus (JET) polarimeter has four lateral channels, whose arrangement is similar to the topology of the diagnostic foreseen in ITER. A statistical analysis of JET polarimetry measurements have been provided in the past for only one vertical channel (CH3) using a polarimetry propagation code based on the Stokes vector formalism. A new propagation code has therefore been developed for the lateral channels to simulate and interpret the measurements of the Faraday rotation (FR) and Cotton-Mouton (CM) phase shift in JET. In this paper, a complete analysis of the integral form of the Stokes equation for the lateral channels is presented. In particular, the analysis shows that there is a strong interaction between the FR and CM effect even at low currents and low magnetic fields. The code results of both FR and CM have been used to estimate the line-integrated density and a proper benchmarking with experimental data has been performed. Two approximations to obtain the electron density in real time, using only plasma current in case of FR measurements and also toroidal magnetic fields in case of CM measurements, are proposed.
ABSTRACT In the past, the analysis of JET polarimetry measurements were carried out only for the ... more ABSTRACT In the past, the analysis of JET polarimetry measurements were carried out only for the vertical channels using a polarimetry propagation code based on the Stokes vector formalism 1 and 2. A new propagation code has been developed therefore for the horizontal chords to simulate and interpret the measurements of the Faraday rotation and Cotton–Mouton phase shift in JET. The code has been used to develop a theoretical study to the effect of the input polarization on the eventual quality of the measurements. The results allow choosing the best polarization to optimize the polarimetric measurements for the various experiments.
ABSTRACT The increasing importance of providing reliable polarimetric measurements in real time, ... more ABSTRACT The increasing importance of providing reliable polarimetric measurements in real time, for both machine protection and plasma control, has motivated the development of a quick version of the calibration algorithms for JET polarimeter. This new code, which interprets the calibration procedure performed before each shot, is based on a physical equivalent model of the diagnostic optical path and is valid for any operational regime of JET. It provides results before the plasma breakdown, and, with its estimates of the optical paths parameters, the polarimetric measurements have an accuracy more than sufficient for real-time purposes. New approximate equations have been validated in order to obtain the line integrated density from the newly calibrated horizontal chords, so that also these polarimetric measurements can also be used for density feedback and machine protection. The availability of reliable polarimetric measurements in real time opens new perspectives also to the determination of the plasma boundary, the magnetic equilibrium, and their use in advanced feedback control schemes.
ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic... more ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic reconstructions in the interior of the plasma column in Tokamaks. In the last years, polarimetry has been increasingly used to provide global constraints to equilibrium codes. Joint European Torus (JET) polarimeter has four lateral channels, whose arrangement is similar to the topology of the diagnostic foreseen in ITER. A statistical analysis of JET polarimetry measurements have been provided in the past for only one vertical channel (CH3) using a polarimetry propagation code based on the Stokes vector formalism. A new propagation code has therefore been developed for the lateral channels to simulate and interpret the measurements of the Faraday rotation (FR) and Cotton-Mouton (CM) phase shift in JET. In this paper, a complete analysis of the integral form of the Stokes equation for the lateral channels is presented. In particular, the analysis shows that there is a strong interaction between the FR and CM effect even at low currents and low magnetic fields. The code results of both FR and CM have been used to estimate the line-integrated density and a proper benchmarking with experimental data has been performed. Two approximations to obtain the electron density in real time, using only plasma current in case of FR measurements and also toroidal magnetic fields in case of CM measurements, are proposed.
ABSTRACT. Real-time simultaneous control of several radially distributed magnetic and kinetic pla... more ABSTRACT. Real-time simultaneous control of several radially distributed magnetic and kinetic plasma parameters (such as the safety factor, q (x), and gyro-normalized temperature gradient, ρTe*(x), respectively) is being investigated on JET, in view of developing integrated control of advanced tokamak scenarios and internal transport barriers suitable for ITER. This paper describes the new model-based optimal profile controller which has been tested during the last experimental campaign. The controller aims to use the combination ...
ABSTRACT Recently a complete model of JET polarimeter calibration has been developed. A specific ... more ABSTRACT Recently a complete model of JET polarimeter calibration has been developed. A specific propagation code has also been written to simulate the measurements of both the vertical and horizontal chords during plasma operation. In this paper, these two models have been checked with residual analysis methods valid for nonlinear systems. The differences between the estimates of the codes and the experimental measurements, during both calibration and plasma operation, have been calculated and analysed statistically. The distribution of the residuals confirms the quality of the model developed to interpret the calibration of the diagnostic. On the other hand, during plasma operation, the residuals do not present a Gaussian distribution and there is clear evidence of serial correlation at subsequent times. Correlation analysis with the inputs indicates that problems with the magnetic field topology, provided by an independent equilibrium code, are the source of the inadequacies in the results of the propagation model.
ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic... more ABSTRACT Internal magnetic measurements are essential to obtaining reliable and accurate magnetic reconstructions in the interior of the plasma column in Tokamaks. In the last years, polarimetry has been increasingly used to provide global constraints to equilibrium codes. Joint European Torus (JET) polarimeter has four lateral channels, whose arrangement is similar to the topology of the diagnostic foreseen in ITER. A statistical analysis of JET polarimetry measurements have been provided in the past for only one vertical channel (CH3) using a polarimetry propagation code based on the Stokes vector formalism. A new propagation code has therefore been developed for the lateral channels to simulate and interpret the measurements of the Faraday rotation (FR) and Cotton-Mouton (CM) phase shift in JET. In this paper, a complete analysis of the integral form of the Stokes equation for the lateral channels is presented. In particular, the analysis shows that there is a strong interaction between the FR and CM effect even at low currents and low magnetic fields. The code results of both FR and CM have been used to estimate the line-integrated density and a proper benchmarking with experimental data has been performed. Two approximations to obtain the electron density in real time, using only plasma current in case of FR measurements and also toroidal magnetic fields in case of CM measurements, are proposed.
ABSTRACT In the past, the analysis of JET polarimetry measurements were carried out only for the ... more ABSTRACT In the past, the analysis of JET polarimetry measurements were carried out only for the vertical channels using a polarimetry propagation code based on the Stokes vector formalism 1 and 2. A new propagation code has been developed therefore for the horizontal chords to simulate and interpret the measurements of the Faraday rotation and Cotton–Mouton phase shift in JET. The code has been used to develop a theoretical study to the effect of the input polarization on the eventual quality of the measurements. The results allow choosing the best polarization to optimize the polarimetric measurements for the various experiments.
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Papers by A. Boboc