Analysis and thermal testing to predict operational limits of a unidirectional carbon-carbon composite for thermal imaging diagnostic of high energy particle beams

A widespread system used to diagnose high energy particle beams is calorimetry by interception of the beams themselves with solid tiles. Deposition of beam energy on such tiles will produce local heating areas that will be observed by infrared thermographic cameras to diagnose beam properties like beam layout, uniformity, and divergence. Rear observation has been preferred due to plasma formation at the front intercepting side as the beam will interact with the gas environment at the surface; so a tile material has been developed, manufactured, and tested to transfer the thermal patterns from the front side to the rear observed one. The tile material is a unidirectional carbon-carbon composite with high melting and sublimation temperatures in vacuum and it is made with fibers oriented along the thickness direction in order to realize a high ratio between directional thermal conductivities and so to recognize the beam energy at the front by measuring the temperature field at the rear side. Given the very high expected power densities (up to 20MW/m2 ) on the tile diagnostic and the low transverse thermal conductivity compared to the axial one, very high transverse thermal gradients are expected, just along the direction without any reinforcements. So a matrix-dominated failure mode has been identified to post-process results of a specifically developed parametric, nonlinear, transient, coupled-field finite element model: tile braking is prevented when local thermal deformations are lower than the maximum allowable strains. The finite element model has been validated by comparison with experimental measurements as it is able to identify the failure zone and to predict the tile failure time resulting in a few seconds depending on the parameters of the particle beam. This apparently little utilisation time is not considered an issue as the diagnostic system will be used during the early stage of the machine life, when short pulse durations will be run. Tile material properties are temperature dependent with high non-linearities, so and analytical discussion of such properties is made and results of the finite element model have been post-processed. The purpose of this work is to predict the maximum allowable pulse duration to avoid tile breaking considering different temperature fields given after running of previous pulses and taking into account material non-linearities.