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
TEXTOR is a Tokamak Experiment for Technology Oriented Research in the field of plasma wall interaction. Research revolves around particle and energy exchange between the plasma and the surrounding chamber but also involves active measures to optimize the first wall and the plasma boundary region in such a way that wall erosion, particle release and impurity influx to the plasma core are reduced to tolerable levels.
In 1996 the EURATOM associations Institute for Plasmaphysics at Forschungszentrum Jülich, Instituut voor Plasmafysika Rijnhuizen at FOM and LPP-ERM/KMS have founded the Trilateral Euregio Cluster (TEC) in order to conduct a joint research programme at TEXTOR. The TEC enables focusing of resources, produces synergies by combining different expertise and acts as an attracting point for regional universities.
The TEXTOR work centers on the experimental verification of the predicted conjugate-T performance and on the routine application of ICRH as heating source for a variety of experimental programs. The ICRH system of the TEXTOR tokamak consists of two power sources of 2 MW each delivering their power to 2 unshielded antennas located opposite to each other toroidally and operating between 25 and 38 MHz. Each antenna is composed of two toroidally adjacent current straps. One antenna is tuned using a conjugate-T (CT) matching system whereas the second one is matched classically using a stub, a line stretcher and an auto tuning system (AutoT) including 2 variable capacitors that are adjusted by feedback to minimize the reflection. Comparisons between the performance of the CT matching scheme and the AutoT scheme concluded that the CT matching scheme performs better during fast load variations.
Basic plasma physics research on TEXTOR studies the effect of the resonant magnetic perturbations imposed by the Ergodic Divertor both on the intermittent, blob-type edge transport and on the ELMs in H-mode. With the application of the static 6/2 Dynamic Ergodic Divertor, the burst amplitude, the number of large blobs and the velocity of their radial motion are all generally reduced, thus leading to a reduction of the intermittent turbulent particle flux in the scrape off layer. The application of resonant magnetic perturbations (RMP) is regarded as one possible option to control ELMs. The static 6/2 Dynamic Ergodic Divertor does indeed decrease the ELM size with increasing applied perturbation, but at the same time steadily decreases the H-mode pedestal, until the plasma is finally driven back to L-mode.
LPP-ERM/KMS is also involved in the development of ITER relevant scenarios for ICRF assisted tokamak start-up and ICRF wall conditioning (ICWC). The ICRF plasma production technique is considered as a promising alternative tool for the following applications in the present and next generation superconducting fusion machines: (i) wall conditioning in the presence of permanent high magnetic field; (ii) assistance for the tokamak start-up at low inductive electric field (E ~ 0.3 V/m in ITER); (iii) target dense plasma production (ne ≥ 1019 m-3) in stellarators. The ITER WG-6 (Heating and Current Drive) took a decision to put ICWC scenario back to the "Functional Requirements" for the ITER ICH system. Therefore, development of the ITER relevant wall conditioning scenario with standard ICRH antenna is considered as a high demanding task. Wall conditioning experiments are performed on TEXTOR, as well as on ASDEX Upgrade.