Controlled Al melting on DiMES to benchmark MEMOS-U melt layer modeling for ITER

2023 Research Campaign, Advanced Material Evaluation

Purpose of Experiment

The goal of the experiment is to benchmark MEMOS-U melt layer dynamics modeling for ITER using aluminum (Al) as a proxy for beryllium (Be). The practical goal is to obtain shallow (100 – 200 µm thick) melt layer on the surface of the sample oriented towards the incident plasma heat flux. Background: Beryllium melting puts tight constraints on the required performance of the ITER disruption mitigation system, especially in the early years due to lack of experience in avoiding disruptions. Understanding of the macroscopic motion and stability of liquid Be is relevant for transient melting of the first wall during disruptions in ITER. MEMOS-U [1] has been demonstrated to reproduce melt layer motion in the controlled high-Z melting experiments (JET, AUG), but no controlled low-Z melting experiments have been performed in tokamaks so far. The main goal of the present experiment is to benchmark MEMOS-U code for light materials, taking advantage of the newly updated coupled heat transfer, replacement current and fluid motion models capable of predictive ITER studies. Melt layer acceleration of high melting point high-Z materials like W and Mo is dominated by JxB force mainly due to high thermionic emission. With a low melting point metal there will be no significant thermionic emission, thus the importance of secondary melt acceleration mechanisms can be investigated.

Experimental Approach

We will use aluminum as a proxy for beryllium. We will expose an aluminum sample using Divertor Material Evaluation System (DiMES) under controlled L-mode plasma conditions. DiMES head will feature an Al block angled by 30 degrees towards the incoming plasma flux and electrically isolated from the ATJ graphite holder by two boron nitride insulators. The Al block will grounded to the stainless steel holder base via a wire with known resistance (~0.15 Ω), so that the current flowing to the ground can be measured via the signal wire connected to the data acquisition system. A thermocouple will be used to measure the sample temperature. The sample will be imaged by visible and IR cameras. The exposed sample will be analyzed by profilometry then sectioned to reveal characteristics of the melt layer.

See more details, including project leads, at U.S. Department of Energy, Office of Scientific and Technical Information (OSTI).