Posted on: 14th November 2011
Since the last update, commissioning of the heating and current drive systems has been progressing steadily and ‘additional heating’ systems are now routinely being used in daily operations.
Keeping a careful eye on the temperatures of in-vessel components the ICRH heating system has been operated in most of its normal operating modes, e.g. at all the standard frequencies between 33 and 51 MHz. In each mode the power and ‘on-times’ have gradually been increased.
In parallel, the Lower Hybrid Current Drive (LHCD) system has been brought back into operation, and for the first time ever, it is now possible to observe the LHCD launcher from inside the torus, using a newly installed camera system. This offers the opportunity of watching for possible arcing at the mouth of the launcher. As such, this new camera view brings both some interesting physics and a new protection system. Using this camera, it is now possible (in ‘real-time’) to observe the launcher moving forward from its parked position to the operating position close to the edge of the plasma, and then to see a slight ‘shimmering’ of the light as power is applied. Then the launcher moves back as the pulse draws to a close.
JET’s main additional heating comes from the Neutral Beam Injection (NBI) system. As described in the shutdown weekly series, this system has been considerably upgraded with a lot of new hardware. Both the power supplies and the beam sources (PINIs) have been enhanced. Bringing the NBI system back into operation has taken longer than planned, but beams have been produced successfully in what is called ‘Asynchronous’ mode. This means that the beams are fired at a target inside the Neutral Injection box (NIB) to tune their performance, and that this is done independently of plasma operations of JET. However, for the first time since the shutdown the large valve between the octant 8 NIB and the torus has been opened so that the NBI system can be run in time with a JET pulse. The first careful (very short) bursts of beam power will be run and only when the operators are happy that this is working properly full power beams be will injected.
Each of these small steps brings the machine closer to producing new physics that will be relevant for ITER. The current routine of interspersing commissioning sessions with experimental work is expected to continue until the end of the year.
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.