Carbon Foam for Beam Stop Application

Transformative new user facilities are currently in the planning stages at DoE. These facilities will use a LINAC to accelerate electrons upwards of 2.5GeV to produce free-electron lasers (FELs) output. Afterwards roughly a 750kW electron beam has to be stopped. This amount of power has been conventionally stopped using water baths. Dissipating this amount of energy in water introduces a mobile radionuclide management issue that could be avoided with a highly, thermally conductive foam core beam stop. Conductive POCO graphite foam was initially thought to offer a promising solution to this beam stop problem. Graphite foam, available at density from 0.1 to 0.9 g/cc, certainly increases the radiation length as desired. As a result the energy dissipation per unit length of the dump (the average heat flux) is reduced. Preliminary analysis indicates that graphitic foams (in an XFEL like copper jacket) would allow the use of a single foam core dump per high power beam line. However, available graphitic foams, like POCO, are anisotropic, with thermal conductivities much higher in one direction. These foams do not have the ideal properties for this application due to their level of anisotropy. This would result in a worst case, material failure, and less efficient heat transfer. Allcomps isotropic variable-density, high conductivity foam has unique potential for solving this problem. Being highly thermally conductive and tailorable in density, it is possible to reach the appropriate beam stop design parameters. Demonstrating its uniqueness, Allcomp produced a 0.5g/cc density version of its foam, and tested specimens over the beam stop operational temperature regime. Foam blocks, in thickness of 3inch (12inch square) and 6inch (12inch square), were produced and foam properties were established, and compared to predictions. Finite element thermal and stress solutions were prepared. Predicted peak temperature results over 20 year radiation exposure period were lower than for solid graphite and well within material limits for the foam. Material processing development will be continued, as well as material tests. Radiation tests at ORNL are planned. Results of radiation damage effects will be measured in terms of change in foam thermal conductivity as function displacement damage per atom (dpa). Phase I analytical study results provided insight into the expected dpa over a 20 year exposure. Commercial Applications and OtherBenefits: Allcomps high conductivity foam opens new opportunities in commercial applications such as a heat spreader in computers, avionics racks, and spaced-based electronics. Our isotropic highly machinable graphitic foam is an ideal core material for HEP sandwich structures.