Electron Temperature Gradient Scale Measurements in ICRF Heated Plasmas at Alcator C-Mod

It is generally believed that the temperature gradient is a driving mechanism for the turbulent transport in hot and magnetically confined plasmas. A feature of many anomalous transport models is the critical threshold value ($L_{C})$ for the gradient scale length, above which both the turbulence and the heat transport increases. This threshold is also predicted by the recent multi-scale gyrokinetic simulations, which are focused on addressing the electron (and ion) heat transport in tokamaks [Howard \textit{et al}, Phys. Plasma \textbf{23}, 056109 (2016)]. Recently, we have established an accurate technique (B$_{\mathrm{T}}$-jog) to directly measure the electron temperature gradient scale length ($L_{Te}=T_{e}$/$\nabla T)$ profile, using a high-spatial resolution radiometer-based electron cyclotron emission (ECE) diagnostic [Houshmandyar \textit{et al}, RSI (2016)]. For the work presented here, electrons are heated by ion cyclotron range of frequencies (ICRF) through minority heating in L-mode plasmas at different power levels, TRANSP runs determine the electron heat fluxes and the scale lengths are measured through the B$_{\mathrm{T}}$-jog technique. Furthermore, the experiment is extended for different plasma current and electron densities by which the parametric dependence of $L_{C}$ on magnetic shear, safety factor and density will be investigated.