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Title: Negative current profile measurements in tokamaks using internal Rogowskii coil

Abstract

An internal Rogowskii coil (IRC) has been developed to measure current profiles within SINP tokamak discharges. The present article has highlighted measurements using the IRC in SINP tokamak discharges exhibiting extension in phase after the discharge decays to approximately half its peak value. The IRC current profile results have been compared to that obtained from an internal Langmuir-magnetic probe system and have been observed to measure current profile directly (without employing any reconstruction methods) as well as the localized fluctuations much better than the latter. Interesting observation of negative currents in such Ohmic discharges is reported for the first time. The presence of negative currents has been observed to help in improving the confinement of the discharges. These results are important especially in relation to recent observations of 'current holes', in large fusion devices (such as JET and JT-60U), enhancing confinement properties.

Authors:
;  [1]
  1. Saha Institute of Nuclear Physics, I/AF Bidhannagar, Calcutta 700 064 (India)
Publication Date:
OSTI Identifier:
20778916
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 77; Journal Issue: 3; Other Information: DOI: 10.1063/1.2173032; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CONFINEMENT; CURRENTS; ELECTRIC DISCHARGES; FLUCTUATIONS; JT-60U TOKAMAK; MAGNETIC PROBES; PLASMA; PLASMA DIAGNOSTICS; SINP TOKAMAK

Citation Formats

Narayanan, Ramesh, and Sekar Iyengar, A.N. Negative current profile measurements in tokamaks using internal Rogowskii coil. United States: N. p., 2006. Web. doi:10.1063/1.2173032.
Narayanan, Ramesh, & Sekar Iyengar, A.N. Negative current profile measurements in tokamaks using internal Rogowskii coil. United States. doi:10.1063/1.2173032.
Narayanan, Ramesh, and Sekar Iyengar, A.N. Wed . "Negative current profile measurements in tokamaks using internal Rogowskii coil". United States. doi:10.1063/1.2173032.
@article{osti_20778916,
title = {Negative current profile measurements in tokamaks using internal Rogowskii coil},
author = {Narayanan, Ramesh and Sekar Iyengar, A.N.},
abstractNote = {An internal Rogowskii coil (IRC) has been developed to measure current profiles within SINP tokamak discharges. The present article has highlighted measurements using the IRC in SINP tokamak discharges exhibiting extension in phase after the discharge decays to approximately half its peak value. The IRC current profile results have been compared to that obtained from an internal Langmuir-magnetic probe system and have been observed to measure current profile directly (without employing any reconstruction methods) as well as the localized fluctuations much better than the latter. Interesting observation of negative currents in such Ohmic discharges is reported for the first time. The presence of negative currents has been observed to help in improving the confinement of the discharges. These results are important especially in relation to recent observations of 'current holes', in large fusion devices (such as JET and JT-60U), enhancing confinement properties.},
doi = {10.1063/1.2173032},
journal = {Review of Scientific Instruments},
number = 3,
volume = 77,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • New methods to reconstruct plasma shape and plasma current distribution from magnetic measurements are proposed. The reconstruction of plasma current profile from magnetic measurements is regarded as an optimum allocation problem of currents into cross section of the vacuum vessel of the tokamak. For solving this optimization problem, the authors use two types of solutions: a genetic algorithm and a combined method of a Hopfield neural network and a genetic algorithm. The effectiveness of these methods is shown by the application of these techniques to JT-60U plasmas.
  • The updating of a current density profile measuring technique, based on carbon pellet toroidal acceleration measurements, is described. Taking account of the evaporating pellet shape changes occurring at the final stage of evaporation results in higher electron temperature and current density values. Current density profile measurement results are presented. The density profiles for two different Joule heating regimes of the T-10 tokamak were measured by means of the technique discussed. Mutually correlated singularities of the current-density and safety factor profiles are discussed. 4 refs., 2 figs.
  • Low aspect ratio tokamaks (LART) with aspect ratios A = R/a < 2 were proposed by Y.-K.M. Peng and D.J. Strickler. This tokamak concept attracts much attention in two respects. First, such a tokamak is a powerful tool for plasma physics research due to the properties of its magnetic configuration. Second, it is a promising fusion device able to steadily confine high-pressure plasmas. These tokamaks are compact, hence, such a tokamak as a laboratory research apparatus would be a fairly low-cost device. To date, there is only one experiment with such a plasma, on the START device. The experimental conditionsmore » were sufficiently close to the tokamak ones. It was shown that the thermal confinement of a plasma with A = 1.3 - 1.4 was at least not worse than that predicted by the LART phenomenological scaling. One of the LART features is a high plasma current density. Hence, LART tokamaks could have a high energy release. That is why one can expect the LARTs to operation in the enhanced energy confinement regime (H-mode), even in the case of a sole ohmic heating. It has been noted that the LART plasma has a vertically elongated equilibrium configuration cross section. The author investigates factors which could influence this elongation, and the shape of the plasma current distribution.« less