Dependence of the threshold for perturbation field generated<i>m</i>/<i>n</i>= 2/1 tearing modes on the plasma fluid rotation

Koslowski, H. R.; Liang, Y.; Krämer‐Flecken, A.; Löwenbrück, K.; Hellermann, M. von; Westerhof, E.; Wolf, R. C.; Zimmermann, O.

doi:10.1088/0029-5515/46/8/l01

Cited by 85 publications

(130 citation statements)

References 15 publications

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“…Recently it was shown on TEXTOR that the relative frequency between the mode and the helical field is important in determining the field penetration [5,6], being in agreement with theoretical results [7][8][9].…”

Section: Introductionsupporting

confidence: 69%

“…(a) Helical field penetration: For the plasma being originally stable to tearing modes, an applied resonant helical field (or error fields of experimental devices) can penetrate through the resonant surface and generate a magnetic island there [1][2][3][4][5][6][7][8][9]. Recently it was shown on TEXTOR that the relative frequency between the mode and the helical field is important in determining the field penetration [5,6], being in agreement with theoretical results [7][8][9].…”

Section: Introductionmentioning

confidence: 65%

“…Cold ion assumption is made here since the ion temperature is significantly lower than the electron's in the considered experiments [5,6].…”

Section: Computational Modelmentioning

confidence: 99%

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Effect of resonant helical magnetic fields on plasma rotation

Günter

Finken

2009

Physics of Plasmas

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The effect of a resonant helical magnetic field on plasma rotation is investigated numerically based on the two fluid equations. It is found that, depending on the frequency and the direction of the original plasma rotation, a static helical field of a small amplitude can either increase or decrease the rotation speed. With increasing the field amplitude, the plasma rotation frequency approaches the electron diamagnetic drift frequency but rotates in the ion drift direction. These

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Section: Introductionsupporting

confidence: 69%

Section: Introductionmentioning

confidence: 65%

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Effect of resonant helical magnetic fields on plasma rotation

Günter

Finken

2009

Physics of Plasmas

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“…In the presence of a plasma, the magnetic topology changes due to shielding currents that are generated on the rational q surfaces. For these experiments, this results in a plasma in which only a 2=1 island is destabilized when the current in the DED coils exceeds a threshold [8]. In the underlying work, 1 kHz ac DED currents are used, resulting in a poloidal rotation of 500 Hz for the m=n 2=1 island which is locked to the rotating perturbation field.…”

mentioning

confidence: 99%

Effect of Heating on the Suppression of Tearing Modes in Tokamaks

et al. 2007

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The suppression of (neoclassical) tearing modes is of great importance for the success of future fusion reactors like ITER. Electron cyclotron waves can suppress islands, both by driving noninductive current in the island region and by heating the island, causing a perturbation to the Ohmic plasma current. This Letter reports on experiments on the TEXTOR tokamak, investigating the effect of heating, which is usually neglected. The unique set of tools available on TEXTOR, notably the dynamic ergodic divertor to create islands with a fully known driving term, and the electron cyclotron emission imaging diagnostic to provide detailed 2D electron temperature information, enables a detailed study of the suppression process and a comparison with theory. Tearing modes, and, in particular, neoclassical tearing modes (NTMs), have a deleterious effect on the performance and stability of tokamak plasmas. Larger tokamaks, like the proposed ITER tokamak, are more susceptible to the formation of NTMs. It is therefore important to develop techniques to control or suppress them and to gain understanding of the suppression process. Islands can be stabilized by driving a (helical) current perturbation inside the island region. Gyrotrons are an ideal tool for the localized generation of this current through the injection of radio frequency waves into the plasma. This current can either be directly driven noninductively by electron cyclotron current drive (ECCD) [1] or indirectly by heating the island by electron cyclotron resonance heating (ECRH) [2 -4], causing a helical perturbation to the Ohmic current due to the temperature dependence of the plasma conductivity. ECCD is thought to be a more efficient way to suppress (neoclassical) islands. The tearing mode suppression by heating is often neglected. In this Letter, it will be shown that on TEXTOR the physical mechanism at work during heating can be clearly identified. It is demonstrated that also heating gives a sizeable suppression of the islands.A set of tearing mode suppression experiments on the TEXTOR tokamak is described, that focuses on the suppression by heating (ECRH). In TEXTOR, suppression by ECRH dominates over ECCD [5] due to the low current drive efficiency (low T e ).TEXTOR is a medium sized limiter tokamak with a circular plasma cross section (R 0 1:75 m, a 0:46 m) and is ideally suited for island suppression studies due to the unique combination of available tools. With the dynamic ergodic divertor [6], islands can be created and controlled with (in contrast to other tokamaks) a fully known driving term. The gyrotron can be used to generate highly localized EC waves inside the island. Finally, the process of suppression can be observed in detail by the 2D electron cyclotron emission imaging (ECEI) diagnostic [7].The dynamic ergodic divertor (DED) on TEXTOR is a perturbation field experiment consisting of 16 helical coils on the high field side, aligned with the q 3 field lines. Figure 1(a) shows the vacuum field used for the experiments described in this Letter...

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“…27 The 2/1 tearing mode is locked to the 2/1 perturbation field of the DED, synchronizing its rotation with the DED frequency. High reproducibility of these DED induced 2/1 tearing modes provides for a suitable target for physics study 28 and for the development of a closed-loop feedback control system for tearing mode suppression.…”

Section: A Dynamic Ergodic Divertormentioning

confidence: 99%

Development and testing of a fast Fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization

Thoen

Bongers

Westerhof

et al. 2009

Review of Scientific Instruments

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Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. A fast Fourier transform ͑FFT͒ based wide range millimeter wave diagnostics for spectral characterization of scattered millimeter waves in plasmas has been successfully brought into operation. The scattered millimeter waves are heterodyne downconverted and directly digitized using a fast analog-digital converter and a compact peripheral component interconnect computer. Frequency spectra are obtained by FFT in the time domain of the intermediate frequency signal. The scattered millimeter waves are generated during high power electron cyclotron resonance heating experiments on the TEXTOR tokamak and demonstrate the performance of the diagnostics and, in particular, the usability of direct digitizing and Fourier transformation of millimeter wave signals. The diagnostics is able to acquire 4 GHz wide spectra of signals in the range of 136-140 GHz. The rate of spectra is tunable and has been tested between 200 000 spectra/s with a frequency resolution of 100 MHz and 120 spectra/s with a frequency resolution of 25 kHz. The respective dynamic ranges are 52 and 88 dB. Major benefits of the new diagnostics are a tunable time and frequency resolution due to postdetection, near-real time processing of the acquired data. This diagnostics has a wider application in astrophysics, earth observation, plasma physics, and molecular spectroscopy for the detection and analysis of millimeter wave radiation, providing high-resolution spectra at high temporal resolution and large dynamic range.

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Dependence of the threshold for perturbation field generatedm/n= 2/1 tearing modes on the plasma fluid rotation

Cited by 85 publications

References 15 publications

Effect of resonant helical magnetic fields on plasma rotation

Effect of resonant helical magnetic fields on plasma rotation

Effect of Heating on the Suppression of Tearing Modes in Tokamaks

Development and testing of a fast Fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization

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