  The observation of distinct peaks in tokamak core reflectometry measurements
- named quasi-coherent-modes (QCMs) - are identified as a signature of
Trapped-Electron-Mode (TEM) turbulence [H. Arnichand et al. 2016 Plasma Phys.
Control. Fusion 58 014037]. This phenomenon is investigated with detailed
linear and nonlinear gyrokinetic simulations using the \gene code. A Tore-Supra
density scan is studied, which traverses through a Linear (LOC) to Saturated
(SOC) Ohmic Confinement transition. The LOC and SOC phases are both simulated
separately. In the LOC phase, where QCMs are observed, TEMs are robustly
predicted unstable in linear studies. In the later SOC phase, where QCMs are no
longer observed, ITG modes are identified. In nonlinear simulations, in the ITG
(SOC) phase, a broadband spectrum is seen. In the TEM (LOC) phase, a clear
emergence of a peak at the TEM frequencies is seen. This is due to reduced
nonlinear frequency broadening of the underlying linear modes in the TEM regime
compared with the ITG regime. A synthetic diagnostic of the nonlinearly
simulated frequency spectra reproduces the features observed in the
reflectometry measurements. These results support the identification of core
QCMs as an experimental marker for TEM turbulence
