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Title: On neutral-beam injection counter to the plasma current

Abstract

It is well known that when neutral beams inject ions into trapped orbits in a tokamak, the transfer of momentum between the beam and the plasma occurs through the torque exerted by a radial return current. It is shown that this implies that the angular momentum transferred to the plasma can be larger than the angular momentum of the beam, if the injection is in the opposite direction to the plasma current and the beam ions suffer orbit losses. On the Mega-Ampere Spherical Tokamak (MAST) [R. J. Akers, J. W. Ahn, G. Y. Antar, L. C. Appel, D. Applegate, C. Brickley et al., Plasma Phys. Controlled Fusion 45, A175 (2003)], this results in up to 30% larger momentum deposition with counterinjection than with co-injection, with substantially increased plasma rotation as a result. It is also shown that heating of the plasma (most probably of the ions) can occur even when the beam ions are lost before they have had time to slow down in the plasma. This is the dominant heating mechanism in the outer 40% of the MAST plasma during counterinjection.

Authors:
; ;  [1];  [2]
  1. EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom)
  2. (France)
Publication Date:
OSTI Identifier:
20782344
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 12; Journal Issue: 11; Other Information: DOI: 10.1063/1.2121287; (c) 2005 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; ANGULAR MOMENTUM; ANGULAR MOMENTUM TRANSFER; BEAM INJECTION HEATING; CHARGED-PARTICLE TRANSPORT; ELECTRIC CURRENTS; IONS; MAST TOKAMAK; PARTICLE LOSSES; PLASMA; PLASMA BEAM INJECTION; PLASMA CONFINEMENT; ROTATION; TRAPPING

Citation Formats

Helander, P., Akers, R.J., Eriksson, L.-G., and Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, F-13108 St. Paul lez Durance. On neutral-beam injection counter to the plasma current. United States: N. p., 2005. Web. doi:10.1063/1.2121287.
Helander, P., Akers, R.J., Eriksson, L.-G., & Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, F-13108 St. Paul lez Durance. On neutral-beam injection counter to the plasma current. United States. doi:10.1063/1.2121287.
Helander, P., Akers, R.J., Eriksson, L.-G., and Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, F-13108 St. Paul lez Durance. Tue . "On neutral-beam injection counter to the plasma current". United States. doi:10.1063/1.2121287.
@article{osti_20782344,
title = {On neutral-beam injection counter to the plasma current},
author = {Helander, P. and Akers, R.J. and Eriksson, L.-G. and Association EURATOM-CEA, CEA/DSM/DRFC, CEA Cadarache, F-13108 St. Paul lez Durance},
abstractNote = {It is well known that when neutral beams inject ions into trapped orbits in a tokamak, the transfer of momentum between the beam and the plasma occurs through the torque exerted by a radial return current. It is shown that this implies that the angular momentum transferred to the plasma can be larger than the angular momentum of the beam, if the injection is in the opposite direction to the plasma current and the beam ions suffer orbit losses. On the Mega-Ampere Spherical Tokamak (MAST) [R. J. Akers, J. W. Ahn, G. Y. Antar, L. C. Appel, D. Applegate, C. Brickley et al., Plasma Phys. Controlled Fusion 45, A175 (2003)], this results in up to 30% larger momentum deposition with counterinjection than with co-injection, with substantially increased plasma rotation as a result. It is also shown that heating of the plasma (most probably of the ions) can occur even when the beam ions are lost before they have had time to slow down in the plasma. This is the dominant heating mechanism in the outer 40% of the MAST plasma during counterinjection.},
doi = {10.1063/1.2121287},
journal = {Physics of Plasmas},
number = 11,
volume = 12,
place = {United States},
year = {Tue Nov 15 00:00:00 EST 2005},
month = {Tue Nov 15 00:00:00 EST 2005}
}
  • A significant particle pinch and reduction of the effective thermal diffusivity are observed after switching the neutral beam direction from coinjection to counterinjection in the JFT-2M tokamak. The particle pinch measured in the counterinjection phase shows good agreement with the prediction of the inward pinch model related to the electric fields.
  • Core electron temperature profile flattening is observed in a large helical device [A. Iiyoshi et al. Nucl. Fusion 39, 1245 (1999)] inward shifted plasma with counter-neutral beam injection. To study this phenomenon, heat pulse experiments are performed by on-axis electron cyclotron heating power modulation. A unique feature of heat pulse propagation is observed near the m/n=2/1 rational surface (m, n are the poloidal and toroidal mode numbers, respectively). A simultaneous response of the temperature perturbation on radially separated flux surfaces is shown. The change in the magnetic field topology due to the presence of a magnetic island structure can explainmore » this nonmonotonic heat pulse propagation. The estimated O-point position of the island is located near the m/n=2/1 rational surface.« less
  • In the JT-60U negative-ion-based neutral beam injection system, the effect of negative ion and electron deflection by the plasma grid (PG) magnetic filter was studied. After a long-pulse operation of up to 19 s, a local melting was observed on the beamline near the ion source, facing the electron drift side of the PG magnetic field. It is confirmed that the experimental deflection of the negative-ion beam agrees well with the three-dimensional beam simulation result by taking account of the measured magnetic field. By using the code, it is found that some stripped electrons produced in the first acceleration gapmore » pass through the down pitch of the multiple apertures in the next stage of acceleration grids, and then collide on the beamline around the melted location.« less
  • When significant neutral beam power is injected in the direction counter to the plasma current in the DIII-D tokamak [{ital Plasma} {ital Physics} {ital and} {ital Controlled} {ital Nuclear} {ital Fusion} {ital Research} 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159], a prompt reduction in electrostatic turbulence is observed, principally in shorter wavelength modes. The core radial electric field reverses polarity and becomes sheared as the fluctuations reduce. As the electric field continues evolving, a larger reduction is observed on a slower time scale. These observations support the possibility of controlling turbulence and its associated transport bymore » controlling the internal radial electric field. {copyright} {ital 1996 American Institute of Physics.}« less