Localized direct electron heating by mode-converted ion cyclotron range of frequencies (ICRF) waves in D(H) tokamak plasmas has been clearly observed for the first time in Alcator C-Mod. Both on- and off-axis (high field side) mode conversion electron heating (MCEH) have been observed. The MCEH profile was obtained from a break in slope analysis of electron temperature signals in the presence of rf (radio frequency) shut-off. The temperature was measured by a 32-channel high spatial resolution (7 mm) 2nd harmonic heterodyne electron cyclotron emission (ECE) system. The experimental profiles were compared with the predictions from a toroidal full-wave ICRF code TORIC. Using the hydrogen concentration measured by a high-resolution optical spectrometer, TORIC predictions were shown qualitatively in agreement with the experimental results for both on- and off-axis MC cases. From the simulations, the electron heating from mode converted ion cyclotron wave (ICW) and ion Bernstein wave (IBW) is examined.

Using an effective relaxation time model, the effects of ion-ion and ion-neutral collisions on quasilinear ion heating by the current-driven ion cyclotron instability in the high latitude ionosphere have been studied. For conditions typical of the high latitude lower (200-300 km) F-region ionosphere, it is found that the combined effects of ion-neutral and ion-ion collisions tend to isotropize (S(tet)/T(par) approx. 1) the perpendicular T(per) and parallel S(tet) ion temperatures on time scales on the order of several tens to hundreds of NO+ cyclotron periods for wave amplitudes e(phi)/T sub e = 0.2. Here, phi is the wave electrostatic potential, T(par) the electron temperature (in energy units), e is the electron charge. In addition, for the high latitude upper (600 km) F-region ionosphere it is found that stronger anisotropy (T(per)/T(par)> 3) can be sustained even in the presence of ion collisions with waves with amplitudes e(phi)/T sub e = 0.2. For larger amplitude waves e(phi)/T sub e = 0.4, we find that the heating is weakly anisotropic at low altitudes (200-300 km) and strongly anisotropic at higher (600 km) altitudes. In both wave amplitude regimes (0.2 and 0.4), we find perpendicular ion heating factors about 2-10 for altitudes in the range 300-600km, with the larger perpendicular heating occurring at higher altitudes and larger wave amplitudes. The results are compared with recent rocket and satellite observations in the high latitude ionosphere. Keywords: Ion cyclotron instability; Ion heating. (jhd).