Neutron emission spectroscopy of radio frequency heated (D)T plasmas

The energy spectrum of the d + t -> alpha + n neutron emission has been measured in experiments carried out at JET for plasmas of deuterium–tritium subjected to minority ion cyclotron resonance heating (ICRH) tuned to deuterium. The data obtained with the magnetic proton recoil spectrometer were of sufficient quality to distinguish up to three spectral components of neutron emission some of which were time resolved. A new analysis model was used to derive information on the underlying deuteron velocity distributions and their corresponding energy densities in the plasma. This experiment represents the first use of neutron emission spectroscopy for detailed diagnosis of the response of fusion plasmas to the applied ICRH power for different plasma conditions, including the time evolution over the heating pulse duration for individual discharges. In particular, ICRH effects on the plasma, together with the power absorption mechanisms, were studied as a function of the minority ion concentration in the range 9–20%.