The effects of light impurities, such as helium, boron or carbon, on Alfvén wave dispersion characteristics are studied. It is shown that a small population of light impurities in a hydrogen plasma can strongly modify the dispersion of the global Alfvén waves and the Alfvén continuum. It is also shown that the global Alfvén wave enters into the Alfvén continuum. Under these conditions, it is possible to heat the plasma core efficiently by using an antenna with a narrow toroidal wavelength spectrum. The relationship between impurity concentration and the efficiency of Alfvén wave heating is demonstrated. This effect is explored via a series of numerical calculations of the heating conditions specifically for the Tokamak Chauffage Alfvén wave heating experiment in Brazil (TCA/BR) (1996 Nucl. Fusion 30 503).
Guided propagation of Alfven waves in a toroidal plasma