Limiter Lock Systems at TEXTOR: Flexible Tools for Plasma-Wall Investigation

Abstract

Limiter lock systems on the top and the bottom of the TEXTOR vessel are essential elements for experimental investigations of plasma-wall interaction in a tokamak. The lock systems are designed as user facilities that allow the insertion of wall elements (limiter) and tools for diagnostic (electrical probes, gas injection) without breaking the TEXTOR vacuum. The specially designed holder on top of the central carrier and a powerful vacuum pump system permit the exchange of components within ;1 h. Up to ten electrical signals, four thermocouples, and a gas supply can be connected at the holder interface. Between discharges, the inserted component can be positioned radially and turned with respect to the toroidal magnetic field. Additionally, the central carrier is electrically isolated to apply bias voltages and currents up to 1 kV and 1 kA, respectively. An important feature of the lock system is the good access for optical spectroscopic observation of the inserted components in the vicinity of the edge plasma. The whole spectrum from ultraviolet to infrared is covered by spectrometers and filters combined with cameras. Toroidally and poloidally resolved measurements are obtained from the view on top of the probes while the tangential poloidal view delivers radially and toroidally resolved information. A programmable logic controller (Simatic S5) that is operated inside the TEXTOR bunker and from remote locations outside the concrete wall drives all possible features of the lock system.

Melt-layer ejection and material changes of three different tungsten materials under high heat-flux conditions in the tokamak edge plasma of TEXTOR

“…Experiments were carried out by introducing a limiter made of a graphite carrier with dedicated tungsten plates within inlets (compare [3][4][5]) into the deuterium plasma by means of the PWI-test facilities [6] at TEXTOR (R = 1.75 m a = 0.47 cm) [7]. Two materials are being tested apart from the previously used materials (Plansee or A.L.M.T.…”

Castellated structures for ITER: Differences of impurity deposition and fuel accumulation in the toroidal and poloidal gaps

“…Two types of The limiter was exposed in the SOL of TEXTOR using the Limiter Lock system [18] at the radial distance of R=46.5 cm, 0.5 cm outside the Last Closed Flux Surface (LCFS). 16 repetitive identical NBI-heated discharges were performed with total plasma duration of 112 seconds.…”

Fuel re-absorption by thermally treated co-deposited carbon layers

“…A photograph taken after exposure ( figure 1(b)) demonstrates the frontal view of the test limiter with the attached samples. It was inserted into the vacuum vessel from the top using a transfer system at limiter lock number 3, which is dedicated to material testing in TEXTOR [16]. The block was positioned in the scrape-off layer (SOL) plasma.…”