  Measurement of locked mode (LM) is important for the physical research of
Magnetohydrodynamic (MHD) instabilities and plasma disruption. The n = 0
pick-up need to be extracted and subtracted to calculate the amplitude and
phase of the LM. A new method to extract this pick-up has been developed by
predicting the n = 0 pick-up brn=0 by the LM detectors based on Neural Networks
(NNs) in J-TEXT. An approach called Power Multiple Time Scale (PMTS) has been
developed with outstanding regressing effect in multiple frequency ranges.
Three models have been progressed based on PMTS NNs. PMTS could fit the brn=0
on the LM detectors with little errors both in time domain and frequency
domain. The n>0 pick-up brn>0 generated by resonant magnetic perturbations
(RMPs) can be obtained after subtracting the extracted brn=0. This new method
uses only one LM instead of 4 LM detectors to extract brn=0. Therefore, the
distribution of the LM detectors can also be optimized based on this new
method.
