Mechanism of central temperature peaking in impurity seeded plasmas
نویسنده
چکیده
Formation of a centrally peaked profile of the ion temperature by impurity seeding has been observed in all the largest tokamaks: JET, JT-60U, TFTR. A possible explanation of this phenomenon is proposed, which takes into account the suppression of ion temperature gradient instability induced anomalous transport through increasing ion effective charge Zeff and Doppler shift of unstable modes, S⊥. The particular importance of the S⊥ component proportional to the temperature gradient, which stems from the pressure gradient and neoclassical poloidal rotation, is elucidated. It is demonstrated that this contribution grows significantly by impurity seeding when the rotation regime changes due to increased collisionality. An interrelation between the heating power density and Zeff necessary for the transition to a peaked ion temperature is found. The modification of radial profiles by impurity seeding is modelled numerically and the results are in agreement with the experimental data from JET.
منابع مشابه
Double Transport Barrier Plasmas in Alcator C-Mod
Double transport barrier plasmas comprised of an edge enhanced Dα (EDA) H-mode pedestal and an internal transport barrier (ITB) have been observed in Alcator C-Mod. The ITB can be routinely produced in ICRF heated plasmas by locating the wave resonance off-axis near |r/a| ∼ 0.5, provided the target plasma average density is above ∼1.4 × 10/m, and can develop spontaneously in some Ohmic H-mode d...
متن کاملNonlinear neoclassical transport in a rotating impure plasma with large gradients
Related Articles High-performance double-filter soft x-ray diagnostic for measurement of electron temperature structure and dynamics Rev. Sci. Instrum. 83, 10E129 (2012) Molybdenum emission from impurity-induced m = 1 snake-modes on the Alcator C-Mod tokamak Rev. Sci. Instrum. 83, 10E517 (2012) Extreme ultraviolet spectroscopy and modeling of Cu on the SSPX Spheromak and laser plasma “Sparky” R...
متن کاملImpurity toroidal rotation and transport in Alcator C-Mod ohmic h-mode plasmas
Central toroidal rotation and impurity transport coe cients have been determined in Alcator C-Mod Ohmic High Con nement Mode (H-mode) plasmas from observations of x-ray emission following impurity injection. Rotation velocities up to 3 10 m/s in the co-current direction have been observed in the center of the best Ohmic H-mode plasmas. Purely Ohmic H-mode plasmas display many characteristics si...
متن کاملOn Impurity Handling in High Performance Stellarator/Heliotron Plasmas
The Large Helical Device (LHD) and Wendelstein 7-X (W7-X, under construction) are experiments specially designed to demonstrate long pulse (quasi steady-state) operation, which is an intrinsic property of Stellarators and Heliotrons. Significant progress was made in establishment of high performance plasmas. A crucial point is the increasing impurity confinement towards high density as observed...
متن کاملClassical confinement and outward convection of impurity ions in the MST RFP
Related Articles Modeling of non-stationary local response on impurity penetration in plasma Phys. Plasmas 19, 042502 (2012) Measurement of plasma current dependent changes in impurity transport and comparison with nonlinear gyrokinetic simulation Phys. Plasmas 19, 056110 (2012) Impurity transport in temperature gradient driven turbulence Phys. Plasmas 19, 032313 (2012) Impurity transport due t...
متن کامل