Detection of Alpha Heating in JET-ILW DT Plasmas by a Study of the Electron Temperature Response to ICRH Modulation

Detection of a-particle heating in DT plasmas with fusion gain <1 is difficult by steady-state power balance analysis, since the a power source is small compared to the external heating and escapes a clear identification due to experimental uncertainties. A new detection method has been attempted in the recent JET DTE2 campaign, based on the dynamic response of the electron temperature Te to modulated Ion Cyclotron Resonance Heating (ICRH). ICRH modulation induces both a modulation in Ti (therefore in a-particles from thermal-thermal fusion reactions) and a modulation in fast D or T ions from Neutral Beam Injection (NBI), depending on the chosen ICRH scheme (therefore a modulation in a-particles from beam-thermal/beam-beam fusion reactions). This modulated electron heating from a -particles has a longer phase delay with respect to ICRH power than most other electron heating sources, due to the high energy and long slowing down time of the a-particles, resulting in a delayed Te response in comparison to the Ti response. Such feature, if observed, may then be clearly identified as due to a-particle heating with the help of detailed integrated modelling.