Abstract
The thesis comprises four papers related to sawtooth oscillations in tokamak plasmas and the concomitant redistribution of fast ions. First we present a semi-analytical approach, using line-of-sight measurements of D-D fusion neutrons from neutral beam heated plasmas, to analyze the sawtooth-induced redistribution of the fast neutral beam injected deuterium ions. Comparisons with JET experiments confirm that a large fraction of the central fast ions are expelled from the center. Recent q-profile measurements in tokamak plasmas indicate that q{sub 0} remains below unity throughout a sawtooth cycle, in contradiction with present then theories. We propose a new model, involving full reconnection of the magnetic field lines in two current layers and providing a self-consistent description of the plasma evolution during the sawtooth cycle. Although the plasma redistribution is large, q(r) may remain almost unchanged. We derive a theory for the redistribution of fast ions during sawtooth oscillations and apply it to the sawtooth models of Kadomtsev and our own. Analytical scalings of the change of neutron emission in neutral beam heated plasma are obtained and the implications of the two sawtooth models are compared. Extensive numerical simulations of the flux to the JET neutron profile monitor are carried out, indicating that
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Citation Formats
Wising, F.
Sawtooth oscillations in tokamak plasmas.
Sweden: N. p.,
1992.
Web.
Wising, F.
Sawtooth oscillations in tokamak plasmas.
Sweden.
Wising, F.
1992.
"Sawtooth oscillations in tokamak plasmas."
Sweden.
@misc{etde_10145680,
title = {Sawtooth oscillations in tokamak plasmas}
author = {Wising, F}
abstractNote = {The thesis comprises four papers related to sawtooth oscillations in tokamak plasmas and the concomitant redistribution of fast ions. First we present a semi-analytical approach, using line-of-sight measurements of D-D fusion neutrons from neutral beam heated plasmas, to analyze the sawtooth-induced redistribution of the fast neutral beam injected deuterium ions. Comparisons with JET experiments confirm that a large fraction of the central fast ions are expelled from the center. Recent q-profile measurements in tokamak plasmas indicate that q{sub 0} remains below unity throughout a sawtooth cycle, in contradiction with present then theories. We propose a new model, involving full reconnection of the magnetic field lines in two current layers and providing a self-consistent description of the plasma evolution during the sawtooth cycle. Although the plasma redistribution is large, q(r) may remain almost unchanged. We derive a theory for the redistribution of fast ions during sawtooth oscillations and apply it to the sawtooth models of Kadomtsev and our own. Analytical scalings of the change of neutron emission in neutral beam heated plasma are obtained and the implications of the two sawtooth models are compared. Extensive numerical simulations of the flux to the JET neutron profile monitor are carried out, indicating that both sawtooth models are consistent with data. At last we derive a simplified model for fast ion redistribution at sawteeth, appropriate for describing e.g. low time resolution triton burn-up measurements. The predictions for the post-crash triton profile depends on the radius of q=1, and compares well with JET experiments as well as with the more detailed model above. (35 refs.).}
place = {Sweden}
year = {1992}
month = {Nov}
}
title = {Sawtooth oscillations in tokamak plasmas}
author = {Wising, F}
abstractNote = {The thesis comprises four papers related to sawtooth oscillations in tokamak plasmas and the concomitant redistribution of fast ions. First we present a semi-analytical approach, using line-of-sight measurements of D-D fusion neutrons from neutral beam heated plasmas, to analyze the sawtooth-induced redistribution of the fast neutral beam injected deuterium ions. Comparisons with JET experiments confirm that a large fraction of the central fast ions are expelled from the center. Recent q-profile measurements in tokamak plasmas indicate that q{sub 0} remains below unity throughout a sawtooth cycle, in contradiction with present then theories. We propose a new model, involving full reconnection of the magnetic field lines in two current layers and providing a self-consistent description of the plasma evolution during the sawtooth cycle. Although the plasma redistribution is large, q(r) may remain almost unchanged. We derive a theory for the redistribution of fast ions during sawtooth oscillations and apply it to the sawtooth models of Kadomtsev and our own. Analytical scalings of the change of neutron emission in neutral beam heated plasma are obtained and the implications of the two sawtooth models are compared. Extensive numerical simulations of the flux to the JET neutron profile monitor are carried out, indicating that both sawtooth models are consistent with data. At last we derive a simplified model for fast ion redistribution at sawteeth, appropriate for describing e.g. low time resolution triton burn-up measurements. The predictions for the post-crash triton profile depends on the radius of q=1, and compares well with JET experiments as well as with the more detailed model above. (35 refs.).}
place = {Sweden}
year = {1992}
month = {Nov}
}