Opened in 1983, “JET, based at the Culham Centre for Fusion Energy (CCFE), UK, is the central research facility of the European Fusion Programme, and it is the largest and most successful fusion experiment in the world. JET is collectively used under EUROfusion management by more than 40 European laboratories. Over 350 scientists and engineers from all over Europe contribute to the JET programme.” Source:

As of 2018, JET is the closest to achieving net energy. Considering that that is not their objective they have done very well.