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Title: Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands

Abstract

Electron beam wire tomography in the H-1NF heliac enables high resolution mapping of vacuum flux surfaces with minimal disruption of the plasma operations schedule. Recent experimental results have proven this technique to be a highly accurate and high resolution method for mapping vacuum magnetic islands. Islands of width as small as {delta}{approx}8 mm have been measured, providing estimates of the internal rotational transform of the island. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, enables systematic exploration of magnetic islands and surfaces of interest. Recent development of a fast mapping technique significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields. This article presents recent experimental results and associated techniques.

Authors:
; ;  [1]
  1. Plasma Research Laboratory, Research School of Physical Sciences and Engineering, The Australian National University, Canberra ACT 0200 (Australia)
Publication Date:
OSTI Identifier:
20953236
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 78; Journal Issue: 1; Other Information: DOI: 10.1063/1.2424453; (c) 2007 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; BEAM-PLASMA SYSTEMS; COMPARATIVE EVALUATIONS; ELECTRON BEAMS; MAGNETIC FIELDS; MAGNETIC ISLANDS; MAGNETIC SURFACES; MAGNETOHYDRODYNAMICS; MAPPING; PLASMA; PLASMA CONFINEMENT; PLASMA DIAGNOSTICS; PLASMA INSTABILITY; ROTATIONAL TRANSFORM; STELLARATORS; TOMOGRAPHY

Citation Formats

Kumar, Santhosh T. A., Blackwell, Boyd D., and Harris, Jeffrey H. Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands. United States: N. p., 2007. Web. doi:10.1063/1.2424453.
Kumar, Santhosh T. A., Blackwell, Boyd D., & Harris, Jeffrey H. Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands. United States. doi:10.1063/1.2424453.
Kumar, Santhosh T. A., Blackwell, Boyd D., and Harris, Jeffrey H. Mon . "Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands". United States. doi:10.1063/1.2424453.
@article{osti_20953236,
title = {Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands},
author = {Kumar, Santhosh T. A. and Blackwell, Boyd D. and Harris, Jeffrey H.},
abstractNote = {Electron beam wire tomography in the H-1NF heliac enables high resolution mapping of vacuum flux surfaces with minimal disruption of the plasma operations schedule. Recent experimental results have proven this technique to be a highly accurate and high resolution method for mapping vacuum magnetic islands. Islands of width as small as {delta}{approx}8 mm have been measured, providing estimates of the internal rotational transform of the island. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, enables systematic exploration of magnetic islands and surfaces of interest. Recent development of a fast mapping technique significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields. This article presents recent experimental results and associated techniques.},
doi = {10.1063/1.2424453},
journal = {Review of Scientific Instruments},
number = 1,
volume = 78,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Electron-beam wire-tomography in the H-1NF heliac enables high resolution mapping of vacuum flux surfaces without significant disruption of plasma operations. Recent experimental results have proved this technique to be a highly accurate and high resolution method for mapping vacuum magnetic islands. Islands of width as small as 8 mm have been measured, providing estimates of the internal rotational transform of the island. Point-to-point comparison of the mapping re- sults with computer tracing, in conjunction with an image warping technique, enables systematic exploration of magnetic islands and surfaces of interest. Recent development of a fast mapping technique significantly reduced the mappingmore » time and made this technique suitable for mapping at higher magnetic fields. This paper presents recent experimental results and associated techniques.« less
  • This paper reports an experimental observation of spontaneous transition of the core radial electric field to a large positive value (E(r) similar to 5 kV m(-1)), with a strong electric-field shear (similar to 700 kV m(-2)) in a low temperature (T(e) similar to 10 eV) radio frequency generated argon plasma in the H-1NF heliac stellarator. The transition, which seems to be driven by a spontaneous excitation of m = 2 magnetic islands near the core, is associated with a localized increase in the plasma density and excitation of coherent low frequency (similar to 3 kHz) oscillations possibly due to unstablemore » E(r) shear driven modes. Evidence suggests development of the core electron-root scenario, which previously has been observed only at high temperature electron cyclotron heated plasmas.« less
  • Plasma confinement in the vicinity of vacuum magnetic islands near the magnetic axis in the H-1NF heliac [S. M. Hamberger et al., Fusion Technol. 17, 123 (1990)] has been experimentally studied in a low temperature argon plasma. Experimental results indicate that, under favorable conditions, these low order (m=2) islands near the core of the plasma serve as 'pockets' of higher electron density. This results in significant profile modifications including enhancement of the core radial electric field to a large positive value, possibly through an electron-root ambipolar condition. The characteristics of islands are found to be dependent on the plasma collisionalitymore » and island width.« less
  • Simulations of three-dimensional equilibria in the H-1 Heliac [Fusion Technol. {bold 17}, 123 (1990)] with the HINT code [Phys. Fluids B {bold 4}, 1539 (1992)] show that the size of a dangerous magnetic island should increase with plasma pressure, but that a destruction of the equilibrium at low {beta} is avoided because the rotational transform evolves to exclude the rational surface concerned. At higher pressures there is evidence of near-resonant flux surface deformations, which may lead to an equilibrium limit. A reconnected equilibrium at still higher pressures exhibits a double island structure, which is similar to homoclinic phase portraits thatmore » have been observed after separatrix reconnection in Hamiltonian systems. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less
  • Experimental investigation is conducted to get insight into convective heat transfer features of the aqueous magnetic fluid flow over a fine wire under the influence of an external magnetic field. The convective heat transfer coefficient of the aqueous magnetic fluid flow around the heated wire is measured in both the uniform magnetic field and the magnetic field gradient. The effects of the external magnetic field strength and its orientation on the thermal behaviors of the magnetic fluids are analyzed. The experimental results show that the external magnetic field is a vital factor that affects the convective heat transfer performances ofmore » the magnetic fluids and the control of heat transfer processes of a magnetic fluid flow can be possible by applying an external magnetic field. (author)« less