Posted on: 2nd April 2012

Since last week’s report there has been good progress in implementing the new capabilities of JET. Neutral beam heating power has now reached 21MW and routinely and reliably operated at 16 to 18MW.

Now that the PEWS2 system is commissioned, and the Neutral Beam Local Manager is operating for both Octant 4 and Octant 8 beams, the experimentalists are able to control the delivered power in real time for the first time since operations were restarted.  This factor, along with the availability of a substantial amount of heating, has opened up the opportunity for some interesting experiments.

During a few recent operational sessions, JET has been operating in a way known as the ‘hybrid scenario’ and producing new physics results which are delighting the experimentalists.  This hybrid scenario is achieved by ramping up the plasma current rapidly, and then using high additional heating early in the pulse before the current profile is fully relaxed. In these experiments the confinement properties of the plasma are markedly improved and high ‘plasma pressure’ reached, which is a very desirable result for next-step fusion devices.  It would mean working at lower plasma current, which in turn reduces disruption forces.

Many are surprised to find how quickly JET has reached the level of performance achieved with the old carbon wall.  The outcome will be published at conferences in the normal way, but the sense of excitement in the JET Control Room suggests that good results are being achieved.

Background information
Following on from the popular Shutdown Weekly, this series aims to give an insight into day-to-day activities at JET, from an engineering perspective. It aims to explain the technical aspects of operation of the world’s most successful tokamak. JET’s new ITER-Like Wall is being exploited for the benefit of its future successor, ITER.