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P: Plasmaphysik

P 8: Magnetic Confinement

P 8.3: Vortrag

Dienstag, 18. März 2003, 16:10–16:30, FO2

Efficiency of Electron Cyclotron Current Drive in Tokamak Plasma — •Esmaeil Farshi — FOM-Instituut voor Plasmafysica "Rijnhuizen", Postbus 1207, NL-3430 BE Nieuwegein, Netherlands

The use of electron cyclotron waves for the generation and sustainment of plasma current in tokamaks is of considerable interest. The efficiency of this process is defined as the ratio of current generated to power dissipated. In the presence of electron cyclotron current drive (ECCD) it follows from the circuit equation that a part, P_el, of the wave power is converted directly to electromagnetic energy, P_el=Ẇ−P_ext+V²/R_Sp. Where W≡ LI²/2 is the poloidal field energy, P_ext≡ V_extI is the power coupled from the external circuits. In Ref. [1] the ECCD efficiency has been obtained using the value of W_s that can be interpreted as the energy imparted to the electric field by an electron as it slows down. In particular, what matter is the ratio of the incremental energy that flows into the field to the incremental energy injected into an electron by the waves, i.e. this efficiency can be written as [1]: P_el/P_rf=S·(∂/∂ v)W_s(v)/S·(∂/∂ v)є(v). Where P_rf is the total rf power injected into the plasma and S(r,v,t) is wave-induced flux. In Ref. [1], the effect of the rf induced inductance has not been considered and W_s was taken from the stationary solution of the adjoint equation of the Fokker-Planck equation. Since the induced inductance affects the total plasma inductance, it can change the efficiency through W≡ LI²/2. The ECCD efficiency including the effect of rf induced inductance is obtained and compared to predictions of Ref. [1] and experimental results.

[1] C. F. F. Karney and N. J. Fisch, Phys. Fluids 29(1), 180 (1986).