Application of tungsten for plasma limiters in TEXTOR

Three different types of W limiters were exposed in the TEXTOR plasma and the response of the plasma and materials performance of the limiters were investigated.1. lk limiter operated with preheating above 800 K withstood a plasma heat load of about ∼20 MW/m2 for a few seconds with some slight surface melting during the highest heat load shot. However, it was severely damaged when operated at around 500 K. twin test limiter, half made of bulk W and the other half of graphite (EK-98) gave very useful information on how low- and high-Z materials behave under conditions of simultaneous utilization as PFM such as cross-contamination and the influence of a large mass difference on hydrogen reflection and deposition. ts of main poloidal W limiters made of vacuum vapor sprayed (VPS)-W deposited on graphite (IG-430U) with a Re interlayer could absorb about 60% of the total convection heat and the ohmic plasma with a density as high as 5 × 1013 cm−3 was sustained. Most of the VPS-W coated limiters tolerated a heat load of ∼20 MW/m2. series of W limiters experiments in TEXTOR has shown that W is applicable as a PFM, if its central accumulation is avoided by NBI and/or ICRH heating. Nevertheless, some concerns still remain, including difficulty of plasma start-up, W behavior in higher temperature plasmas, and materialsʹ selection.