Effects of MHD Instabilities on Neutral Beam Current Drive
Authors: M. Podestà , M. Gorelenkova, D.S. Darrow, E.D. Fredrickson, S.P. Gerhardt and R.B. White
Abstract: Neutral beam injection (NBI) is one of the primary tools foreseen for heating, current drive (CD) and q-profile control in future fusion reactors such as ITER and a Fusion Nuclear Science Facility. However, fast ions from NBI may also provide the drive for energetic particle-driven instabilities (e.g. Alfvènic modes - AEs), which in turn redistribute fast ions in both space and energy, thus hampering the control capabilities and overall efficiency of NB-driven current. Based on experiments on the NSTX tokamak [M. Ono et al., Nucl. Fusion 40 (2000) 557], the effects of AEs and other low-frequency MHD instabilities on NB current drive efficiency are investigated. A new fast ion transport model, which accounts for particle transport in phase space as required for resonant AE perturbations, is utilized to obtain consistent simulations of NB current drive through the tokamak transport code TRANSP. It is found that instabilities do indeed reduce the NB-driven current density over most of the plasma radius by up to ~ 50%. Moreover, the details of the current profile evolution are sensitive to the specific model used to mimic the interaction between NB ions and instabilities. Implications for fast ion transport modeling in integrated tokamak simulations are briefly discussed.
_________________________________________________________________________________________________
Prepared for: the 25th IAEA Fusion Energy Conference, St. Petersburg, Russia, 13-18 October 2014.
Papers will be published by the IAEA as unedited proceedings in electronic format on a CD-ROM and on the IAEA Physics Section website:
(http://www-naweb.iaea.org/napc/physics/index.html) by March 2015.
_________________________________________________________________________________________________
Download PPPL-5094 (pdf 2 MB / 7pp)
_________________________________________________________________________________________________