Abstract: The present invention is directed towards an apparatus and method to detect electromagnetic radiation or signals emitted by plasma comprising a sensor unit, the sensing unit comprising a first sensor for detecting electromagnetic radiation or signals; an electromagnetic barrier wherein the electromagnetic barrier is configured to surround the first sensor to prevent ambient electromagnetic radiation reaching the first sensor; a first port through which electromagnetic radiation can pass, the port configured for coupling to a port of a plasma chamber such that electromagnetic radiation or signals emitted from the plasma can reach the first sensor; and a first output coupled with a balun and a dual coaxial system whereby a signal sensed is grounded and a phase reversed version of the signal is grounded. A signal acquisition system (SAS) for detecting electromagnetic radiation emitted by a plasma is also described.

Abstract: The invention provides a system and method for measuring a characteristic of a plasma or a plasma chamber, wherein the plasma chamber has a viewport or a surface which is permeable to electromagnetic radiation such that at least a portion of the electromagnetic radiation emitted by the plasma in the plasma chamber passes through the viewport, the method comprising providing the antenna of a Radio Emission Spectroscopy, RES, plasma bulk system externally to the plasma chamber to absorb at least a portion of the electromagnetic radiation that has passed through the viewport and configured to measure signals in the near-field E- and B-field regions; measuring a first value based on the signal induced in the antenna wherein the signal is obtained from a plurality of powered RF electrodes configured to be independently modulated with one or more power sources; and calculating a second value indicative of a change of magnitude of the characteristic based on a change of magnitude of the first value, wherein the char