One of the main approaches to thermonuclear fusion relies on confining high temperature plasmas with properly shaped magnetic fields. The determination of the magnetic topology is, therefore, essential for controlling the experiments and for achieving the required performance. In Tokamaks, the reconstruction of the fields is typically formulated as a free boundary equilibrium problem, described by the Grad-Shafranov equation in toroidal geometry and axisymmetric configurations. Unfortunately, this results in mathematically very ill posed problems and, therefore, the quality of the equilibrium reconstructions depends sensitively on the measurements used as inputs and on the imposed constraints. In this paper, it is shown how the different diagnostics (Magnetics Measurements, Polarimetry and Motional Stark Effect), together with the edge current density and plasma pressure constraints, can have a significant impact on the quality of the equilibrium on JET. Results show that both the Polarimetry and Motional Stark Effect internal diagnostics are crucial in order to obtain reasonable safety factor profiles. The impact of the edge current density constraint is significant when the plasma is in the H-mode of confinement. In this plasma scenario the strike point positions and the plasma last closed flux surface can change even by centimetres, depending on the edge constraints, with a significant impact on the remapping of the equilibrium-dependent diagnostics and of pedestal physics studies. On the other hand and quite counter intuitively, the pressure constraint can severely affect the quality of the magnetic reconstructions in the core. These trends have been verified with several JET discharges and consistent results have been found. An interpretation of these results, as interplay between degrees of freedom and available measurements, is provided. The systematic analysis described in the paper emphasizes the importance of having sufficient diagnostic inputs and of properly validating the results of the codes with independent measurements. © 2013 Euratom.

Gelfusa, M., Murari, A., Lupelli, I., Hawkes, N., Gaudio, P., Baruzzo, M., et al. (2013). Influence of plasma diagnostics and constraints on the quality of equilibrium reconstructions on Joint European Torus. REVIEW OF SCIENTIFIC INSTRUMENTS, 84(10) [10.1063/1.4824200].

Influence of plasma diagnostics and constraints on the quality of equilibrium reconstructions on Joint European Torus

GELFUSA, MICHELA;GAUDIO, PASQUALINO;Peluso, E;
2013-01-01

Abstract

One of the main approaches to thermonuclear fusion relies on confining high temperature plasmas with properly shaped magnetic fields. The determination of the magnetic topology is, therefore, essential for controlling the experiments and for achieving the required performance. In Tokamaks, the reconstruction of the fields is typically formulated as a free boundary equilibrium problem, described by the Grad-Shafranov equation in toroidal geometry and axisymmetric configurations. Unfortunately, this results in mathematically very ill posed problems and, therefore, the quality of the equilibrium reconstructions depends sensitively on the measurements used as inputs and on the imposed constraints. In this paper, it is shown how the different diagnostics (Magnetics Measurements, Polarimetry and Motional Stark Effect), together with the edge current density and plasma pressure constraints, can have a significant impact on the quality of the equilibrium on JET. Results show that both the Polarimetry and Motional Stark Effect internal diagnostics are crucial in order to obtain reasonable safety factor profiles. The impact of the edge current density constraint is significant when the plasma is in the H-mode of confinement. In this plasma scenario the strike point positions and the plasma last closed flux surface can change even by centimetres, depending on the edge constraints, with a significant impact on the remapping of the equilibrium-dependent diagnostics and of pedestal physics studies. On the other hand and quite counter intuitively, the pressure constraint can severely affect the quality of the magnetic reconstructions in the core. These trends have been verified with several JET discharges and consistent results have been found. An interpretation of these results, as interplay between degrees of freedom and available measurements, is provided. The systematic analysis described in the paper emphasizes the importance of having sufficient diagnostic inputs and of properly validating the results of the codes with independent measurements. © 2013 Euratom.
2013
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore FIS/01 - FISICA SPERIMENTALE
English
Axisymmetric configurations; Equilibrium reconstruction; Grad-Shafranov equations; High-temperature plasmas; Independent measurement; Last closed flux surfaces; Magnetic reconstruction; Motional stark effects, Electric discharges; Ellipsometry; Fusion reactions; Plasma diagnostics; Plasma simulation; Polarimeters; Repair; Safety factor; Stark effect, Magnetoplasma
Gelfusa, M., Murari, A., Lupelli, I., Hawkes, N., Gaudio, P., Baruzzo, M., et al. (2013). Influence of plasma diagnostics and constraints on the quality of equilibrium reconstructions on Joint European Torus. REVIEW OF SCIENTIFIC INSTRUMENTS, 84(10) [10.1063/1.4824200].
Gelfusa, M; Murari, A; Lupelli, I; Hawkes, N; Gaudio, P; Baruzzo, M; Brix, M; Craciunescu, T; Drozdov, V; Meigs, A; Peluso, E; Romanelli, M; Schmuck, ...espandi
Articolo su rivista
File in questo prodotto:
File Dimensione Formato  
RSI_gelfusa_2013.pdf

solo utenti autorizzati

Licenza: Copyright dell'editore
Dimensione 2.33 MB
Formato Adobe PDF
2.33 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/97472
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 11
  • ???jsp.display-item.citation.isi??? 9
social impact