In preparation for testing a lithium-helium heat exchanger at Sandia, unexpected rapid failure of the mild steel lithium preheater due to liquid metal embrittlement occurred when lithium at ~400 °C flowed into the preheater then at ~200 °C. This happened before the helium system was pressurized or heating with electron beams began. The paper presents an analysis of the preheater plus a discussion of some implications for fusion.
The 2016 DIII-D DiMES tungsten (W) leading edge experiment in support of ITER studied heat loads in helium (He) plasmas with ELMs and compound ELMs (C-ELMs). The regime was close to the threshold for L-mode to H-mode transitions. In shots with ECH, C-ELMs produced in H-L back-transitions dominated the transient particle exhaust. Their duration (10–20 ms) was much longer than regular ELMs, and their heat loads higher by 2–3 times. The C-ELMS reduced the plasma density significantly, and some triggered (automated) gas puffing. This regime, with high particle and heat exhaust, may have relevance for He plasmas in ITER's start-up phase. Regular ELMs occurred during neutral beam (NB) powered shots. This paper describes new analyses on heat loads during and between C-ELMs in ECH-powered shot 166843. The results are generally consistent with a geometric solution for the parallel heat load at the plasma edge striking the leading edge. The power in the C-ELMs is sufficient to cause a temperature rise of ∼
Additive Manufacturing (AM) can create novel and complex engineered material structures. Features such as controlled porosity, micro-fibers and/or nano-particles, transitions in materials and integral robust coatings can be important in developing solutions for fusion subcomponents. A realistic understanding of this capability would be particularly valuable in identifying development paths. Major concerns for using AM processes with lasers or electron beams that melt powder to make refractory parts are the power required and residual stresses arising in fabrication. A related issue is the required combination of lasers or e-beams to continue heating of deposited material (to reduce stresses) and to deposit new material at a reasonable built rate while providing adequate surface finish and resolution for meso-scale features. Some Direct Write processes that can make suitable preforms and be cured to an acceptable density may offer another approach for PFCs.
Nygren, Richard E.; Matthews, Guy M.; Morgan, Thomas M.; Silburn, Scot S.; Rosenfeld, John R.; North, Mark N.; Talligro, Alberto T.; Stavila, Vitalie S.
This review of the potential of robust plasma facing components (PFCs) with liquid surfaces for applications in future D/T fusion device summarizes the critical issues for liquid surfaces and research being done worldwide in confinement facilities, and supporting R&D in plasma surface interactions. In the paper are a set of questions and related criteria by which we will judge the progress and readiness of liquid surface PFCs. Part-II (separate paper) will cover R&D on the technology-oriented aspects of liquid surfaces including the liquid surfaces as integrated first walls in tritium breeding blankets, tritium retention and recovery, and safety.
This paper advances a vision for plasma facing components (PFCs) that includes the following points. The solution for plasma facing materials likely consists of engineered structures in which the layer of plasma facing material (PFM) is integrated with an engineered structure that cools the PFM and may also transition with graded composition. The key to achieving this PFC architecture will likely lie in advanced manufacturing methods, e.g., additive manufacturing, that can produce layers with controlled porosity and features such as micro-fibers and/or nano-particles that can collect He and transmutation products, limit tritium retention, and do all this in a way that maintains adequate robustness for a satisfactory lifetime. This vision has significant implications for how we structure a development program.