A gas-turbine plant, comprising a gas-turbine unit and a control system, wherein: the gas-turbine unit comprises a combustion chamber; and the control system comprises monitoring apparatus, provided with at least one optical probe and configured to detect light intensity fluctuations inside the combustion chamber with the optical probe, and a controller, configured to control the gas-turbine unit according to a response of the monitoring apparatus; wherein the monitoring apparatus is configured to convert light intensity signals into optical monitoring signals (S OM) and the controller is configured to supply control signals (S C) for the gas-turbine unit according to the optical monitoring signals (S OM) supplied by the monitoring apparatus; wherein the controller comprises a processing module, configured to detect conditions of thermoacoustic instability inside the combustion chamber based on the optical monitoring signals (S OM); wherein the monitoring apparatus comprises piezoelectric transducers, fluidly coupled to the inside of the combustion chamber and configured to provide pressure monitoring signals (S PM) indicative of pressure inside the combustion chamber; and wherein the processing module is configured to identify correlations between light intensity fluctuations detected by the optical probe and pressure fluctuations detected by the piezoelectric transducers; characterized in that the controller is configured to supply the control signals (S C) for the gas-turbine unit according to the pressure monitoring signals and to detect conditions of thermoacoustic instability inside the combustion chamber according to the correlations between the detected light intensity fluctuations and pressure fluctuations. the gas-turbine unit comprises a combustion chamber; and the control system comprises monitoring apparatus, provided with at least one optical probe and configured to detect light intensity fluctuations inside the combustion chamber with the optical probe, and a controller, configured to control the gas-turbine unit according to a response of the monitoring apparatus; wherein the monitoring apparatus is configured to convert light intensity signals into optical monitoring signals (S OM) and the controller is configured to supply control signals (S C) for the gas-turbine unit according to the optical monitoring signals (S OM) supplied by the monitoring apparatus; wherein the controller comprises a processing module, configured to detect conditions of thermoacoustic instability inside the combustion chamber based on the optical monitoring signals (S OM); wherein the monitoring apparatus comprises piezoelectric transducers, fluidly coupled to the inside of the combustion chamber and configured to provide pressure monitoring signals (S PM) indicative of pressure inside the combustion chamber; and wherein the processing module is configured to identify correlations between light intensity fluctuations detected by the optical probe and pressure fluctuations detected by the piezoelectric transducers; characterized in that the controller is configured to supply the control signals (S C) for the gas-turbine unit according to the pressure monitoring signals and to detect conditions of thermoacoustic instability inside the combustion chamber according to the correlations between the detected light intensity fluctuations and pressure fluctuations.