The present application discloses a device for radical monitoring a plasma source for a remote plasma source used in a processing system and includes at least one gas source, a plasma source body having at least one passage having at least one passage surface, a first thermal sensor receiver may be formed within the plasma source body proximate to the passage surface of the passage, a first thermal sensor positioned within the first thermal sensor receiver configured to measure a first temperature of the passage surface, a second thermal sensor receiver formed within the plasma source body proximate to the passage surface of the passage and configured to measure a second temperature of the passage surface of the passage at a second location.