Kiwamu, Hang

We investigated the nonlinearity in the esd control signal using channel 'SUS-ETMY_L3_MASTER_OUT_UL_DQ'. In the upper panel of the attached plot, the 'linear' is the product of control signal and the bias, 'quadratic' the square of control signal, and 'total' the sum of these two. We did not do an absolute calibration but the relative magnitude should be good enough for the purpose of this study. In the lower panel we showed the coherence between the linear and quaduartic timestreams, with 512s of data and 64 averages.

From the result we can see that the nonlinear term is well below the linear component, and the coherence was low. As a result, it should be safe to use the current ESD configuration without worrying too much about the quadratic term.