High heat flux tests of carbon composites for KSTAR and NSTX

Uncooled samples of various carbon fiber composites (CFCs), nominally 2.50 cm square and 1.00 cm in height were exposed in the Electron Beam Test System (EBTS) to heat fluxes up to ∼100 MW/m² for shots typically of 1.5 s. The heat flux was focused on a square 1 × 1 cm at the center of the sample. For NSTX (National Spherical Torus Experiment), five samples of Allied Signal 2-D CFC Type 865-19-4 were tested with 1.5 s shots at heat fluxes to 120 MW/m². For KSTAR (Korean Superconducting Tokamak Advanced Research) Project, a total of 37 samples of 29 various CFCs were tested. Duplicates samples with thermocouples were used to measure the absorbed heat and to calculate the fraction of the beam power absorbed. The samples were tested to 100 MW/m² with 1.5 s shots and then selected samples were tested at 60 MW/m² for shots up to 3.5 s. The most basic results from all of these tests is that, as expected, none of the samples fractured. For the KSTAR test, some samples achieved higher heat fluxes than others while their surface temperatures remained below a threshold of 2800°C. Other observations presented in the paper are based on post-test examinations of the surface morphologies. The paper was presented in poster form at SOFE99 but not published there and is represented here.