The authors exposed a radiatively cooled, lithium-filled tantalum heat pipe (HP) to a hydrogen plasma in DIFFER’s linear plasma source Magnum PSI continuously for ~2 hours. The beam made a saddle-shaped footprint along the side of the inclined ~195-mm-long HP. During several steps with constant overall heat load, we tilted the HP to vary the peak heat flux by a factor of two. The maximum was ~2.5 MWm2. Diagnostics included near infra-red thermography from two orthogonal ports. Another paper  gives details of the experiment.
The heat pipe operated at ~1000-1100° C. We stopped after a leak in the HP occurred near the beam axis intercept, and ~0.06 g of lithium formed a 6-mm-diameter nodule. A coating that covered roughly half of the area wetted by the beam was also present. The initial breach occurred at a site of prior material damage. A second breach occurred several seconds after the exposure was terminated. Fractography and post-test metallography show the mechanisms differed. With the second breach, a transverse crack, lithium flowed out quickly and wetted an area ~30 mm2. At this point the HP was cooling. If creep and relaxation occurred during the exposure, then stress state reversed (tensile loading) during cooling. A tantalum disk annealed in a hydrogen furnace was available for comparative evidence of hydrogen embrittlement.
Sandia had purchased an existing tantalum HP from Aavid-Thermacore, Inc. The test showed prolonged operation, gave useful data and we judged it a success. However, tantalum would not be the right choice for a future PFC. The paper also discusses the geometry and materials for future PFCs.
 G.F. Matthews, R. Nygren, T. Morgan, S.A. Silburn, “Demonstration of the potential for exchangeable PFCs based on radiatively cooled lithium heat pipes in Magnum PSI,” this conference.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This work was also part-funded by the RCUK Energy Programme under grant EP/I501045.