Ecole Royale Militaire - Koninklijke Militaire School
Avenue de la Renaissance 30, 1000 Brussels
Phone: (+32) 2 742 65 72 Fax: (+32) 2 735 24 21
JET (Joint European Torus) was designed to carry out fusion experiments in conditions close to those of a commercial reactor. JET has been operating since 1983, and is the largest and most powerful magnetic confinement fusion device in the world. Knowledge gained from JET will provide valuable input into the design of "next generation" devices such as ITER. The involvement of LPP-ERM/KMS centers on the development and operation of several ICRH antennas installed on JET, and on the dedicated ICRH physics program.
LPP-ERM/KMS is the lead Association in the JET Enhanced Performance project aiming at constructing and commissioning a JET ITER-like ICRH antenna. The ITER-like antenna has been constructed in an ELM- or load-resilient way, meaning that, although the plasma may vary strongly, this does not translate into large impedance variations, thus allowing the generators to couple RF power to the plasma despite ELMs. As the walls of a future fusion reactor will have to be covered to a high fraction by a blanket and only a small area will be available for systems like antennas, it is important that any heating system features a high power density. The ITER-like antenna at JET will be capable of delivering 8MW/m² to plasmas with ELMs at a relatively large distance between antenna and plasma, which, in turn, is another challenging condition for the ITER ICRH system. The antenna is now installed in JET and is the subject of an intensive commissioning and exploitation phase since March 2008.
LPP-ERM/KMS is also heavily involved in the ICRH physics program at JET. Experiments in the framework of the Taskforce H as well as experiments where RF heating was used as a tool to study the behavior of plasmas, were performed at JET. Below is listed a selection of these experiments:
- Investigations of the efficiency of the D majority heating scheme in conditions relevant for ITER. As the majority heating scheme was expected to be characterized by low single-pass absorptivity, neutral beam ions were adopted not only to pre-heat the plasma to temperatures/collisionalities closer to those of ITER but also to move the Doppler-shifted cyclotron layer of a subset of the energetic particles well away from the cold IC resonance position; majority RF absorption is expected to be poor at the cold resonance. Evidence was found of the beneficial synergistic effect of NBI on RF heating.
- Mode conversion, which allows creating a well-localized heat source in the plasma, is used to study electron heat transport in internal transport barrier (ITB) plasmas.
- Gas puffing in the scrape off layer is able to improve the coupling of ICRH in ITER-like conditions, where the antenna-plasma distance will routinely be significantly larger than the typical distances in present-day machines.
- Design and testing of an α-diagnostic for ITER, improvement of the neutron and γ-ray diagnostics on JET.
- ELM mitigation using external magnetic perturbation coils