The Plasma Diagnostic Group develops high-resolution, ultra-fast multi-channel diagnostics, with the aim to diagnose small-scale structures in hot magnetised plasmas. To stay at the cutting edge, the group pioneers new ideas and technologies. This is often done in collaboration with one or more groups from abroad, to bring together the required expertise. The group is internationally renowned for its expertise in the field of Thomson scattering, microwave diagnostics and works in close collaboration with the Fusion Departement of the University Eindhoven on active beam diagnostics. The ultra-high resolution diagnostics have been fundamental for the research in the field of electron transport physics and Magneto Hydrodynamic stability which are all relevant issues in the context of the FOM program on burn control in fusion plasmas. The scientific questions call for ever-better resolution, which is a drive for the group. But it is equally true that the ever-increasing resolution offered by the developed instruments gives rise to new scientific questions. Figure 1. shows high-resolution 2-D electron cyclotron imaging measurements of a islands induced by external coils in TEXTOR and suppressed by the action of electron cyclotron heating. Apart from developing state-of-the-art equipment to aid the DIFFER research on burn control on TEXTOR, ASDEX-U and JET, the group has constructed a number of diagnostics for other plasma devices. In the past, high-resolution Thomson-scattering systems have been developed for the Russian T-10 tokamak and the Spanish TJ-II stellarator and is highly involved in the development of the charge exchange recombination spectroscopy (CXRS) and LIDAR Thomson scattering diagnostic for ITER.
Additional information can be obtained from the annual report:
- Annual report 2011 - Fusion Research - Plasma Diagnostics
Figure 1: Poloidal reconstruction of the island from the 2D-ECEI data. In the left-most picture, the island, excited by the DED, is present and has a flat temperature profile. In the central picture, taken just after switch on of ECRH, the temperature peaks up. In the right most picture, the island is suppressed due to the increased temperature.
Many of the diagnostic projects have been achieved in the framework of international collaborations. Members of the Plasma Diagnostic group have been involved in international diagnostic working groups to discuss the diagnostics for a number of future generation magnetic confinement devices, including JET, Wendelstein 7-X and ITER. Over the years the number of different diagnostics has been reduced and the emphasis has been put on especially those systems that best serve the physics programme. It is not a coincidence that these are exactly the techniques where DIFFER is at the international forefront.
- The group is continuously pushing the concept of high-resolution Thomson scattering to its extremes as is evidenced by the upgrade of the system to high repetition rate for high resolution density and temperature profile measurements. Evenmore, an upgrade is being prepared for the ADSDEX-U experiment with the aim to measurfe the electron drift (eg. the current density) at the edge of the plasma. Besides this project the group is involved in the preparation of the ITER LIDAR Thomson Scattering diagnostic.
- In the field of microwave diagnostics a close collaboration exists since 1996 with the world-leading microwave group at UC Davis. The ECE Imaging system that was explored by this collaboration, first on RTP and TEXTOR and presently on ASDEX-U, is a completely new concept. Studies revealing the 2D structures of edge localised modes or toroidal Alfven eigenmodes are being carried out. An exciting upgrade to a 3D system is being investigated.
- For the development of the CXRS system for ITER the group works in close contact with the Fusion Departement at the University Eindhoven, TNO and NRG and other the plasma physics institutes in Jülich(D), Culham Centre of Fusion Energy (UK) and Troitsk (Russia). A proto-type spectrometer has been built which is tested at the TEXTOR and ASDEX-U tokamaks.