High harmonic fast waves in high beta plasmas

High harmonic fast magnetosonic waves in high beta plasmas are investigated. In the high beta regime, a combination of reduced group velocity and a high beta enhancement of magnetic pumping lead to such large values of electron absorption that one can expect strong (≊100%) single pass absorption. In particular, by controlling the wave spectrum, the prospect of localized electron heating and current drive appears to be feasible in high beta low-aspect-ratio tokamak regimes. Inclusion of finite-Larmor-radius terms reveals an accessibility limit in the high ion beta regime (βi≊50% for a deuterium plasma) due to mode conversion into an ion-Bernstein-wave-like mode. No similar beta limit is expected for electrons. With increasing ion beta, the ion damping can increase significantly, particularly near the mode-conversion accessibility limit. The presence of an energetic ion component expected during intense neutral beam injection and α heating does not appear to modify the accessibility condition nor cause excessive wave absorption by the energetic ions.