Density fluctuation measurements covering a wavenumber range relevant to ITG, TEM and ETG type instabilities (k⊥ ρi ≈ 0.2→ 10) are compared during Ohmic and neutral beam injection (NBI). These short time duration NBI perturbations modified the background temperature as well as the density fluctuation behaviour but had little effect on the background density. It is found that both the measured and calculated responses to these perturbations varied with wavenumber supporting the need for broad wavenumber comparisons. The experimentally measured fluctuation changes and calculated growth rates (from the linear gyrokinetic code GKS) show qualitative similarities to each other at low and intermediate k while the comparison at high k is inconclusive.
Study of ion-gyroscale fluctuations in low-density L-mode plasmas heated by NBI on KSTAR