The stability of higher harmonic electrostatic electron drift waves in toroidal geometry in studied for a representative plasma profile. Using a model driving function, it is shown that the dissipative trapped electron (DTE) mode admits solutions ω/ωe* ≫ 1 (ωe* is the electron diamagnetic drift frequency) that may relate to density fluctuation measurements which have suggested the presence of such higher frequency modes. Comparison of analytic and numerical results for both outward and inward ballooning DTE modes gives good agreement for the former modes but generally poor agreement for the latter ones. Further, it is found from the numerical results that the inward ballooning modes may be more unstable than the outward ballooning modes, even though the trapped electron drive is maximized on the outboard midplane.
Simulation of density fluctuations before the L-H transition for Hydrogen and Deuterium plasmas in the DIII-D tokamak using the BOUT++ code