Numerical simulation of ion cyclotron range of frequencies electron heating in the JET tokamak

An ion cyclotron range of frequencies (ICRF) full-wave code and an anisotropic quasilinear Fokker–Planck code are used to simulate the time-dependent rise in the electron and ion temperatures during a sawtooth period corresponding to initial Ohmic equilibrium conditions in the JET tokamak [in Plasma Physics and Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. 1, p. 44]. Results from the 1-D power deposition studies indicate that less than 10% of the launched fast wave energy is directly absorbed by the e1ectrons via transit time damping and mode conversion processes over a wide range of the JET plasma equilibrium parameters and wave spectrum. In contrast, the Fokker–Planck results indicate a very fast time scale for the formation of energetic minority tail ions which slow down primarily on electrons. It is concluded that the process of minority ion tail formation and electron drag best explains the experimentally observed rates of electron heating as seen in JET. To further substantiate this point, numerical Fokker–Planck results are presented that yield time-dependent electron and ion temperature rises, which are in good agreement with central core experimenta1 measurements for the appropriate range of observed ICRF power density, energy confinement time, and plasma and wave parameters.