Detection of a-particle heating in DT plasmas with fusion gain <1 is difficult by steady-state power balance analysis, since the a power is small compared to the external heating and falls within experimental uncertainties. A new detection method has been attempted in the 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 (i.e. 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 (i.e. in as from beam-thermal/beam-beam fusion reactions). This modulated electron heating from as has a longer phase delay than most other electron heating sources, due to the a high energy and long slowing down time, resulting in a delayed Te response in comparison to the Ti response. Best results have been obtained in JET DTE2 in the T-rich Hybrid scenario [1] at 3.86 T, 2.5 MA with 15%-85% D-T mix, ~29 MW D NBI power and 4 MW ICRH power in n=1 D scheme, square-wave modulated at 1 Hz with 50% duty-cycle. Fig.1 shows profiles of amplitudes and phases of Te and Ti modulations. Amplitudes are ~ 10% with centrally peaked profiles, as expected. The key result is the large phase delay of central Te with respect to Ti: whilst ions show an expected central phase delay ~ 50 deg, increasing towards the edge, electrons show maximum phase delay in the centre, ~105 deg, decreasing towards values similar to the ion phases when approaching the edge. This is a clear signature of a central Te modulation at least in part due to fast ions with long slowing down times. Modelling of the heating deposition shows that Dbulk and DNBI accelerated by 4 MW n=1 D ICRH form tails up to 250 keV, which boost the fusion reactions and induce the large neutron and a modulation, but do not have long slowing down times to justify the observed Te delay. This indicates that the large phase delay observed in central Te can only be due to a heating. Integrated modelling of the discharge indeed reproduces the experimental results only when a heating is included in the source terms. The estimated time-averaged amount of electron a heating is ~2 MW in the first phase of the pulse and its modulation amplitude ~ 0.5 MW.
Detection of alpha heating in JET-ILW DT plasmas by a study of the electron temperature response to ICRH modulation
Mantica P;Auriemma F;Casiraghi I;Dal Molin A;Rigamonti D;Tardocchi M;
2023
Abstract
Detection of a-particle heating in DT plasmas with fusion gain <1 is difficult by steady-state power balance analysis, since the a power is small compared to the external heating and falls within experimental uncertainties. A new detection method has been attempted in the 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 (i.e. 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 (i.e. in as from beam-thermal/beam-beam fusion reactions). This modulated electron heating from as has a longer phase delay than most other electron heating sources, due to the a high energy and long slowing down time, resulting in a delayed Te response in comparison to the Ti response. Best results have been obtained in JET DTE2 in the T-rich Hybrid scenario [1] at 3.86 T, 2.5 MA with 15%-85% D-T mix, ~29 MW D NBI power and 4 MW ICRH power in n=1 D scheme, square-wave modulated at 1 Hz with 50% duty-cycle. Fig.1 shows profiles of amplitudes and phases of Te and Ti modulations. Amplitudes are ~ 10% with centrally peaked profiles, as expected. The key result is the large phase delay of central Te with respect to Ti: whilst ions show an expected central phase delay ~ 50 deg, increasing towards the edge, electrons show maximum phase delay in the centre, ~105 deg, decreasing towards values similar to the ion phases when approaching the edge. This is a clear signature of a central Te modulation at least in part due to fast ions with long slowing down times. Modelling of the heating deposition shows that Dbulk and DNBI accelerated by 4 MW n=1 D ICRH form tails up to 250 keV, which boost the fusion reactions and induce the large neutron and a modulation, but do not have long slowing down times to justify the observed Te delay. This indicates that the large phase delay observed in central Te can only be due to a heating. Integrated modelling of the discharge indeed reproduces the experimental results only when a heating is included in the source terms. The estimated time-averaged amount of electron a heating is ~2 MW in the first phase of the pulse and its modulation amplitude ~ 0.5 MW.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
