We propose a new activity on verification and validation (V&V) of MHD codes presently employed by the fusion community as a predictive capability tool for liquid metal cooling applications, such as liquid metal blankets. The important steps in the development of MHD codes starting from the 1970s are outlined first and then basic MHD codes, which are currently in use by designers of liquid breeder blankets, are reviewed. A benchmark database of five problems has been proposed to cover a wide range of MHD flows from laminar fully developed to turbulent flows, which are of interest for fusion applications: (A) 2D fully developed laminar steady MHD flow, (B) 3D laminar, steady developing MHD flow in a non-uniform magnetic field, (C) quasitwo-dimensional MHD turbulent flow, (D) 3D turbulent MHD flow, and (E) MHD flow with heat transfer (buoyant convection). Finally, we introduce important details of the proposed activities, such as basic V&V rules and schedule. The main goal of the present paper is to help in establishing an efficient V&V framework and to initiate benchmarking among interested parties. The comparison results computed by the codes against analytical solutions and trusted experimental and numerical data as well as code-to-code comparisons will be presented and analyzed in companion paper/papers.

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Removing the limiters from the HBTX experiment has had the beneficial effect of reducing the loop voltage by about a third. Since the poioidal beta, be, remains largely unaltered there is a corresponding 50% improvement in the energy conhement time. Soft X-ray measurements show a suprathennal tail in the electron energy distribution for the first time. The 156 graphite tiles cover about 8% of the vacuum vessel and protrude 1 cm into the piasma. The consequent drop in loop voltage with their removal is in agreement with models for the loop voltage based on global magnetic helicity balance. The observed changes in the ion temperature are consistent with these models when the energy balance of electrons and ions is also included.

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