Tomographic analysis of compound sawteeth on the Tokamak de Varennes

Janicki, Christian; Simm, C.; Decoste, R.; Pacher, G.W.; Pacher, H.D.

doi:10.1088/0029-5515/30/5/016

Cited by 21 publications

(21 citation statements)

References 16 publications

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“…This is consistent with the flattening process of the pressure profile (current profile) in the full reconnection model. These processes are illustrated in frames [8][9][10][11]. As the heat is removed from the core, the closed field line topology is established and recovers the poloidal symmetry as shown in frame 12.…”

Section: C) 2-d Images Of the Sawtooth Crash At High Field Sidementioning

confidence: 93%

“…As a result, the hot spot deforms into a crescent shape and cooler plasmas are convectively induced into the concave section of the crescent hot spot without any reconnection process. This model was supported by x-ray tomography [10] on the Joint European Tokamak (JET) device; however, a later experimental study [11] on the Tokamak de Varennas (TdeV) device concluded that there exists no unique solution for the image through the inversion process of the chordal measurements of the x-ray tomography when only a limited number of independent viewing lines are used.…”

Section: Background Of the Physics Of The Sawtooth Oscillationmentioning

confidence: 99%

“…X-ray monitoring systems [1] or X-ray tomography [10,11,22] have been routinely employed to study sawtooth oscillations in tokamak plasmas since their discovery. However, the X-ray emission signal from hot plasmas is complex due to the multiple parametric dependence of the emission (electron density, temperature, and impurity content) and the limited number of chordal views in most cases hampers the determination of the uniqueness of each model.…”

Section: Background Of the Physics Of The Sawtooth Oscillationmentioning

confidence: 99%

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Self-organized Te redistribution during driven reconnection processes in high-temperature plasmas

et al. 2006

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Section: C) 2-d Images Of the Sawtooth Crash At High Field Sidementioning

confidence: 93%

Section: Background Of the Physics Of The Sawtooth Oscillationmentioning

confidence: 99%

Section: Background Of the Physics Of The Sawtooth Oscillationmentioning

confidence: 99%

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Self-organized Te redistribution during driven reconnection processes in high-temperature plasmas

et al. 2006

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“…As the hot spot deforms into a crescent shape, the cooler outside portion of the plasma is convectively inducted into the core region, resulting in a flattening of the core pressure profile. This model was experimentally supported by x-ray tomography [12] on the Joint European Tokamak; however, a later experimental study [13] on the Tokamak de Varrenes concluded that the tomographic reconstruction is ill-posed and that there is no unique solution for the image through the inversion process of a limited number of chordal measurements from only a few independent views. The distinctively different evolution of the hot spot and/or cold island formation between the quasi-interchange model and full reconnection model could not be conclusively identified due to the lack of reliable 2D experimental tools.…”

mentioning

confidence: 98%

Comparison Study of 2D Images of Temperature Fluctuations during Sawtooth Oscillation with Theoretical Models

et al. 2006

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High temporal and spatial resolution two-dimensional (2D) images of electron temperature fluctuations were employed to study the sawtooth oscillation in the Toroidal Experiment for Technically Oriented Research tokamak plasmas. The 2D images are directly compared with the expected 2D patterns of the plasma pressure (or electron temperature) from various theoretical models. The observed experimental 2D images are only partially in agreement with the expected patterns from each model: The image of the initial reconnection process is similar to that of the ballooning mode model. The intermediate and final stages of the reconnection process resemble those of the full reconnection model. The time evolution of the images of the hot spot or island is partially consistent to those from the full reconnection model but is not consistent with those from the quasi-interchange model. The ''sawtooth oscillation'' was discovered in the early days of fusion plasma research [1] and is known as the m=n 1=1 internal kink mode, where m and n are poloidal and toroidal mode numbers, respectively. An excellent review of recent research in the field of sawtooth oscillations is given in Ref. [2]. This Letter presents a direct comparison study between experimentally measured highresolution 2D images of electron temperature fluctuations with the relevant 2D pattern from prominent physical models developed for the sawtooth oscillation physics in high temperature plasmas. The experiment was performed in the Toroidal Experiment for Technically Oriented Research (TEXTOR) tokamak plasma, which has a circular cross section, a major radius of 175 cm, and a minor radius of 46 cm [3]. The toroidal magnetic field in the present work was in the range 1.9-2.4 T, and the corresponding plasma current was <305 kA. Key plasma parameters were as follows: The central electron density and temperature are in the range 1:5-2:5 10 19 m ÿ3 and from 1.2 to 1.6 keV, respectively. The corresponding peak toroidal beta is 1:0%, and the average poloidal beta is between 0.3 and 0.5. The toroidal rotation of the plasma varied from 1 to 8 10 4 m=s. The speed of a thermal electron is 6 10 7 m=s. The Alfvén and ion acoustic speeds are 5 10 6 and 7 10 5 m=s, respectively. Using plasma parameters close to the q 1 surface, the characteristic reconnection time ( c ) is 700 s.High-resolution 2D images of the electron temperature fluctuations in TEXTOR have been measured with a 2D electron cyclotron emission imaging (ECEI) system. The basic principle of the technique is similar to that of conventional 1D ECE radiometers [4,5]. The new feature of the ECEI diagnostic is that measurements are done in a 2D matrix of sample volumes. Since the ECEI diagnostic has recently been published elsewhere [6,7], we only briefly mention it here as an introduction to the comparison with theoretical models. The system has 16 vertical 8 horizontal sampling volumes arranged in a 2D matrix of 16 cm vertical 7 cm radial . The vertical full width at half maximum of the central antenna pattern is 2 cm...

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“…Another theoretical model is the 'quasi-interchange' model [8] where the cooler plasma convectively flows into the plasma core and the hot spot evolves into a crescent shape due to the magnetic shear of the m/n/=1/1 mode without any magnetic reconnection process. Experimental verification of such a distinctively different evolution of the hot spot /island between the full reconnection model and the quasi-interchange model has not been conclusive due to the lack of accurate 2-D experimental tools [9]. However, in current density profile measurements [10,11], only slight changes of current density were observed while the reconnection time was much faster than expected on theoretical grounds.…”

Section: High Resolution (Temporal and Spatial) Two Dimensional Imagmentioning

confidence: 97%

First Observation of the High Field Side Sawtooth Crash and Heat Transfer during Driven Reconnection Processes in Magnetically Confined Plasmas

Hk¹,

Nc²,

Donné³

et al. 2005

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Tomographic analysis of compound sawteeth on the Tokamak de Varennes

Cited by 21 publications

References 16 publications

Self-organized Te redistribution during driven reconnection processes in high-temperature plasmas

Self-organized Te redistribution during driven reconnection processes in high-temperature plasmas

Comparison Study of 2D Images of Temperature Fluctuations during Sawtooth Oscillation with Theoretical Models

First Observation of the High Field Side Sawtooth Crash and Heat Transfer during Driven Reconnection Processes in Magnetically Confined Plasmas

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