Temperature gradient scale length measurement: A high accuracy application of electron cyclotron emission without calibration.

Calibration is a crucial procedure in electron temperature (T) inference from a typical electron cyclotron emission (ECE) diagnostic on tokamaks. Although the calibration provides an important multiplying factor for an individual ECE channel, the parameter ΔT/T is independent of any calibration. Since an ECE channel measures the cyclotron emission for a particular flux surface, a non-perturbing change in toroidal magnetic field changes the view of that channel. Hence the calibration-free parameter is a measure of T gradient. B-jog technique is presented here which employs the parameter and the raw ECE signals for direct measurement of electron temperature gradient scale length.