Impact of hydrogen isotope species on microinstabilities in helical plasmas. (3rd June 2016)

• Record Type: Journal Article
• Authors: Nakata, Motoki; Nunami, Masanori; Sugama, Hideo; Watanabe, Tomo-Hiko
• Is Part Of: Plasma physics and controlled fusion. Volume 58:Number 7(2016:Jul.)
• Publication Date: 2016-06-03
• Subjects: helical plasmas -- gyrokinetic simulation -- isotope effects -- microinstabilities -- turbulent transport; Plasma (Ionized gases) -- Periodicals; Controlled fusion -- Periodicals; 530.44
• DOI: 10.1088/0741-3335/58/7/074008
• Languages: English
• ISSNs: 0741-3335

Abstract

Abstract: The impact of isotope ion mass on ion-scale and electron-scale microinstabilities such as ion temperature gradient (ITG) mode, trapped electron mode (TEM), and electron temperature gradient (ETG) mode in helical plasmas are investigated by using gyrokinetic Vlasov simulations with a hydrogen isotope and real-mass kinetic electrons. Comprehensive scans for the equilibrium parameters and magnetic configurations clarify the transition from ITG mode to TEM instability, where a significant TEM enhancement is revealed in the case of inward-shifted plasma compared to that in the standard configuration. It is elucidated that the ion-mass dependence on the ratio of the electron–ion collision frequency to the ion transit one, i.e. ν e i / ω t i ∝ ( m i / m e ) 1 / 2, leads to a stabilization of the TEM for heavier isotope ions. The ITG growth rate indicates a gyro-Bohm-like ion-mass dependence, where the mixing-length estimate of diffusivity yields γ / k ⊥ 2 ∝ m i 1 / 2 . On the other hand, a weak isotope dependence of the ETG growth rate is identified. A collisionality scan also reveals that the TEM stabilization by the isotope ions becomes more significant for relatively higher collisionality in a banana regime.