Electromagnetic preliminary design of the real-time millimetre-wave radar system for the diagnostic of the IFMIF-DONES lithium target

This work describes the electromagnetic preliminary design of a mmWave system that, using radar techniques, can provide the position of the outermost layer of the IFMIF-DONES liquid lithium target, which will lead to the determination of the lithium thickness for safety purposes. Possible perturbations in the liquid lithium curtain with a wavelength in the transversal direction in the tens of mm range could lead to some mm changes in the perturbation amplitude, i.e. the curtain depth, thus leading to the necessity of an incident radar-beam spot illuminating the transversal wavelength in the same tens of mm range. Additionally, no movable parts are advisable in an environment so harsh, which naturally points to a phased array design for the system antenna. A tentative design will be explored using theoretical calculations of a phased array that, given the space constraints, needs to be placed in the near-field region. Thus, both the number of array elements and the working frequency will be determined, leading to a theoretical near-field spot size. In addition, considering the long distances involved between the electronics (located in a separate room with good shielding) and the antenna position (close to the lithium target), propagation loss calculations for different waveguide technologies have been performed in order to make an initial proposal for the signal routing and the proper waveguide technology to guide the mmWave signal.