TY - JOUR
T1 - The effects of electron cyclotron heating and current drive on toroidal Alfvén eigenmodes in tokamak plasmas
JF - Plasma Physics and Controlled Fusion
Y1 - 2018
A1 - Sharapov, S. E.
A1 - M. García-Muñoz
A1 - van Zeeland, M. A.
A1 - Bobkov, V.
A1 - Classen, I. G. J.
A1 - Ferreira, J.
A1 - Figueiredo, A. C. A.
A1 - Fitzgerald, M.
A1 - Galdon-Quiroga, J.
A1 - Gallart, D.
A1 - Geiger, B.
A1 - Gonzalez-Martin, J.
A1 - Johnson, T. J.
A1 - Lauber, P.
A1 - Mantsinen, M.
A1 - Nabais, F.
A1 - Nikolaeva, V.
A1 - Sanchis-Sanchez, L.
A1 - Rodriguez-Ramos, M.
A1 - Adrian Schneider, P.
A1 - Snicker, A.
A1 - Vallejos, P.
AB - Dedicated studies performed for Toroidal AEs (TAEs) in ASDEX-Upgrade (AUG) discharges with monotonic q-profiles have shown that electron cyclotron resonance heating (ECRH) can make TAEs more unstable. In these AUG discharges, energetic ions driving TAEs were obtained by ion cyclotron resonance heating (ICRH). It was found that off-axis ECRH facilitated TAE instability, with TAEs appearing and disappearing on timescales of a few milliseconds when the ECRH power was switched on and off. On-axis ECRH had a much weaker effect on TAEs, and in AUG discharges performed with co- and counter-current electron cyclotron current drive (ECCD), the effects of ECCD were found to be similar to those of ECRH. Fast ion distributions produced by ICRH were computed with the PION and SELFO codes. A significant increase in Te caused by ECRH applied off-axis is found to increase the fast ion slowing down time and fast ion pressure causing a significant increase in the TAE drive by ICRH-accelerated ions. TAE stability calculations show that the rise in Te causes also an increase in TAE radiative damping and thermal ion Landau damping, but to a lesser extent than the fast ion drive. As a result of the competition between larger drive and damping effects caused by ECRH, TAEs become more unstable. It is concluded, that although ECRH effects on AE stability in present-day experiments may be quite significant, they are determined by the changes in the plasma profiles and are not particularly ECRH specific.
VL - 60
IS - 1
U1 - FP
U2 - PEPD
U5 - a554715ace8a9dfdbbd2c8c9fb85c210
ER -
TY - JOUR
T1 - TORBEAM 2.0, a paraxial beam tracing code for electron-cyclotron beams in fusion plasmas for extended physics applications
JF - Computer Physics Communications
Y1 - 2018
A1 - Poli, E.
A1 - Bock, A.
A1 - Lochbrunner, M.
A1 - Maj, O.
A1 - Reich, M.
A1 - Snicker, A.
A1 - Stegmeir, A.
A1 - Volpe, F.
A1 - Bertelli, N.
A1 - Westerhof, E.
A1 - Bilato, R.
A1 - Conway, G. D.
A1 - Farina, D.
A1 - Felici, F.
A1 - Figini, L.
A1 - Fischer, R.
A1 - Galperti, C.
A1 - Happel, T.
A1 - Lin-Liu, Y. R.
A1 - Marushchenko, N. B.
A1 - U. Mszanowski
A1 - Poli, F. M.
A1 - Stober, J.
A1 - Zille, R.
A1 - Peeters, A. G.
A1 - Pereverzev, G. V.
KW - Electron cyclotron waves
KW - Magnetic confinement
KW - Paraxial beam tracing
KW - Plasma physics
KW - Wave-plasma interactions
AB - The paraxial WKB code TORBEAM (Poli, 2001) is widely used for the description of electron-cyclotron waves in fusion plasmas, retaining diffraction effects through the solution of a set of ordinary differential equations. With respect to its original form, the code has undergone significant transformations and extensions, in terms of both the physical model and the spectrum of applications. The code has been rewritten in Fortran 90 and transformed into a library, which can be called from within different (not necessarily Fortran-based) workflows. The models for both absorption and current drive have been extended, including e.g. fully-relativistic calculation of the absorption coefficient, momentum conservation in electron–electron collisions and the contribution of more than one harmonic to current drive. The code can be run also for reflectometry applications, with relativistic corrections for the electron mass. Formulas that provide the coupling between the reflected beam and the receiver have been developed. Accelerated versions of the code are available, with the reduced physics goal of inferring the location of maximum absorption (including or not the total driven current) for a given setting of the launcher mirrors. Optionally, plasma volumes within given flux surfaces and corresponding values of minimum and maximum magnetic field can be provided externally to speed up the calculation of full driven-current profiles. These can be employed in real-time control algorithms or for fast data analysis.

VL - 225
U1 - FP

U2 - IMM

U5 - 0a1c01a94caffb41c92a033957ecb032
ER -