Feedback control of the current profile on Tore Supra

Wijnands, T.; Houtte, D. van; Martín, G.; Litaudon, X.; Froissard, P.

doi:10.1088/0029-5515/37/6/i06

Cited by 69 publications

(66 citation statements)

References 19 publications

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“…Linear stability properties are investigated with the CASTOR code [Kerner89], which gives the linear growth rate of resistive MHD modes in toroidal geometry. They show the existence of stable domains for q min >2 and for 1.5>q min >1, in agreement with the analysis of past experiments [Wijnands94,Litaudon96,Zabiego01]. But most of the explored domain is MHD unstable, including the point where the record pulses have been performed with a remarkable reliability (see figure 2).…”

supporting

confidence: 89%

MHD stability of fully non-inductive discharges in Tore Supra

Maget¹,

Imbeaux²,

Huysmans³

et al. 2005

Nucl. Fusion

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Fully non-inductive discharges are performed on the Tore Supra tokamak using Lower Hybrid (LH) waves in a current drive scheme. The MHD aspect is a crucial issue for these discharges, since after hitting an MHD limit it may run into a regime where a strong permanent MHD activity develops. This so-called MHD regime [Maget04] degrades fast electron confinement as well as LHCD efficiency and electron confinement in the plasma core. In the 2003 campaign, a milestone has been reached with the injection of more than 1 GJ of energy in the tokamak, in stationary discharges lasting more than 6 minutes. But the MHD regime has been encountered in several discharges, while the record discharges have shown a very stationary (m=3, n=2) MHD activity in the plasma core without triggering the MHD regime (see figure 1).With the exploration of several global parameters such as the toroidal magnetic field (B), the parallel refractive index of LH waves (n // ) and the total plasma current (I p ), a map of MHD properties for fully non-inductive discharges has been drawn. This is achieved by extrapolating in I p reference magnetic equilibriums from stationary pulses, while imposing a constant shape of pressure and current profiles, and a poloidal beta β p~1 /I p . Note that in the experimental conditions explored, the LH deposition profile is globally peaked, but hollow in the very core, and the region of reversed magnetic shear extends while n // increases.Linear stability properties are investigated with the CASTOR code [Kerner89], which gives the linear growth rate of resistive MHD modes in toroidal geometry. They show the existence of stable domains for q min >2 and for 1.5>q min >1, in agreement with the analysis of past experiments [Wijnands94, Litaudon96, Zabiego01]. But most of the explored domain is MHD unstable, including the point where the record pulses have been performed with a remarkable reliability (see figure 2). Saturated tearing modes are indeed observed in several cases without triggering the deleterious MHD regime.Considering the non-linear evolution of MHD modes is necessary for discrimination between harmless saturated modes and the MHD regime. A particular pulse where a slow ramp down of the total plasma current was performed up to the triggering of the MHD regime allows to identify the mechanism of transition. It can be attributed to the full reconnection of the double tearing mode, which flattens the electron temperature profile up to the outer resonant surface. Its condition of occurrence can be estimated from the calculation of the helical flux relative to the resonant surface q=m/n: ( ) q n m d − = ∫ / * ψ ψ . The full reconnection happens when ψ * is close to zero at the outer resonant surface [Carreras79]. The domain where the MHD regime can be triggered is therefore approximately given by the condition m/n>q min >q( ) 0 * = outer ψ. Such an evaluation is consistent with the experimental points where the MHD regime is indeed triggered (see figure 3), although a safe interval exists for q min slightly belo...

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supporting

confidence: 89%

MHD stability of fully non-inductive discharges in Tore Supra

Maget¹,

Imbeaux²,

Huysmans³

et al. 2005

Nucl. Fusion

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“…2,3 Among scenarios identified to have the potential for high plasma pressure and confinement steady-state operation, the negative or very low central magnetic shear regime is likely one of the most attractive. 2,3 Among scenarios identified to have the potential for high plasma pressure and confinement steady-state operation, the negative or very low central magnetic shear regime is likely one of the most attractive.…”

Section: Introductionmentioning

confidence: 99%

Tomography of the fast electron bremsstrahlung emission during lower hybrid current drive on TORE SUPRA

Peysson

Imbeaux

1999

Review of Scientific Instruments

102

116

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A new tomography dedicated to detailed studies of the fast electron bremsstrahlung emission in the hard x-ray ͑HXR͒ energy range between 20 and 200 keV during lower hybrid ͑LH͒ current drive experiments on the TORE SUPRA tokamak ͓Equipe TORE SUPRA, in / A1-5, p. 105͔ is presented. Radiation detection is performed by cadmium telluride semiconductors, which have most of the desirable features for a powerful diagnosing of magnetically confined hot plasmas-compact size, high x-ray stopping efficiency, fast timing characteristics, good energy resolution, no sensitivity to magnetic field, reasonable susceptibility to performance degradation from neutron/␥-induced damages. This instrument is made of two independent cameras viewing a poloidal cross-section of the plasma, with respectively 21 and 38 detectors. A coarse spectrometry-8 energy channels-is carried out for each chord, with an energy resolution of 20 keV. The spatial resolution in the core of the plasma is 4-5 cm, while the time sampling may be lowered down to of 2-4 ms. Powerful inversion techniques based on maximum entropy or regularization algorithms take full advantage of the large number of line-integrated measurements for very robust estimates of the local HXR profiles as a function of time and photon energy. A detailed account of main characteristics and performances of the diagnostic is reported, as well as preliminary results on LH current drive experiments.

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“…Some previous works show the possibility of controlling profile shape parameters, for instance on Tore Supra: [8], where the current profile shape is characterized by the internal inductance and the central safety factor value and experimental results are presented; and [9], where the control of the width of the lower hybrid power deposition profile is shown and experimentally validated. Also, [10] proposes a discrete real-time control of the steadystate q-profile, considering some possible operating modes.…”

Section: Introductionmentioning

confidence: 99%

Lyapunov-based distributed control of the safety-factor profile in a tokamak plasma

Argomedo¹,

Witrant²,

Prieur³

et al. 2013

Nucl. Fusion

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Abstract.A real-time model-based controller is developed for the tracking of the distributed safety-factor profile in a tokamak plasma. Using relevant physical models and simplifying assumptions, theoretical stability and robustness guarantees were obtained using a Lyapunov function. This approach considers the couplings between the poloidal flux diffusion equation, the time-varying temperature profiles and an independent total plasma current control. The actuator chosen for the safety factor profile tracking is the Lower Hybrid Current Drive, although the results presented can be easily extended to any non-inductive current source. The performance and robustness of the proposed control law is evaluated with a physics-oriented simulation code on Tore Supra experimental test cases.

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Feedback control of the current profile on Tore Supra

Cited by 69 publications

References 19 publications

MHD stability of fully non-inductive discharges in Tore Supra

MHD stability of fully non-inductive discharges in Tore Supra

Tomography of the fast electron bremsstrahlung emission during lower hybrid current drive on TORE SUPRA

Lyapunov-based distributed control of the safety-factor profile in a tokamak plasma

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