Insights of the JET high fusion power scenario in the final DT campaign
In its lifetime of around 40 years of scientific operations, JET has performed three full-scale DT experimental campaigns: one in 1997 (DTE1) and two more in a relatively quick succession in 2021 (DTE2) and 2023 (DTE3). One of the goals of these campaigns, apart from studying variety of physics effect relevant to DT plasmas, was demonstration of fusion power at large scale compatible with JET specifications. The focus was also made on the sustainability of the plasma, i.e. ability to keep the fusion power at high amplitude for extended duration of time: 5 seconds, matching the engineering limits of JET. This was found to be especially challenging after tungsten plasma facing components were implemented during the JET-ILW upgrade in 2009-2011. In DTE2 the highest performing plasma (from the released fusion power point of view) has demonstrated Efus=59MJ of fusion energy from a single discharge. The fusion power averaged over 5 seconds interval was <Pfus>5s=10.1MW. In the final DT campaign DTE3 the scenario performance has been extended to Efus=69MJ from a single discharge and <Pfus>5s=12.4MW. The average fusion power generation efficiency averaged over the same period was <Q>5s=<Pfus>/<Pin>=0.36. The main goal of the additional high fusion power pulses in DTE3 was to demonstrate better sustainability of the discharges, as in all cases in DTE2 where the maximum fusion power was reached, the plasmas suffered from core impurity accumulation. This was only partially successful, as the progressive cooling down of the plasma core due to excessive core radiation could not be avoided, but was slowed down sufficiently to demonstrate significantly higher <Pfus> over the desired 5 second period.