Design Of A Dedicated ECE Diagnostic For Feedback Control Of Instabilities By ECRH

Efficient stabilisation of tearing modes is achieved by placing the ECRH deposition profile exactly over the spatial profile of the mode. Therefore the location of the island with respect to the ECRH deposition profile needs to be known accurately, while this information also needs to be available quickly in order to respond in time within the growth of the NTM. A scheme to detect NTMs is under development that utilises the ECRH transmission line as an ECE receiver thus eliminating the need to compute the coordinates of the island. The receiver needs to operate in an extreme dynamic range in the power spectrum as the ECE components are in the order of nWs while the gyrotron component is at hundreds of kWs.