Exploring magnetic confinement fusion plasma-material interaction: the road to the BiGyM linear device

GyM [1] is a linear plasma device (LPD) operating at Istituto per la Scienza e Tecnologia dei Plasmi, CNR, Milan, with the aim of studying the plasma-material interaction (PMI) for magnetic confinement nuclear fusion applications (commonly known as plasma-wall interaction, PWI). GyM is part of the portfolio of the EUROfusion facilities and one of the LPDs of the EU Contracting Party involved in the IEA's Collaborative Program on PWIs. GyM plasma density is in the range of 1015-1017 m-3, while the electron and ion temperatures are <15 eV and ~0.1 eV, respectively. The ion flux of <1021 m-2s-1 is suitable to mimic the ion and chargeexchange neutral fluxes impinging on tokamaks main chamber, outside the divertor. We shall review the main experimental findings showing (i) how GyM is a valuable testbed for the materials candidate for this region of the tokamak first wall, as Eurofer-97, e.g., of which we have studied the erosion dynamics in detail. GyM's contribution to the field of PWI does not end here. Indeed, it has been used to: (ii) preliminarily characterize divertor-relevant materials, like the investigation of the deuterium (D) retention of liquid tin (Sn), and obtain spectroscopic data, such as the S/XB values of Sn and tungsten (W), and (iii) develop new diagnostic methods, devoted, e.g., to the absolute quantification of the ammonia produced in nitrogen-seeded D plasmas. PWI research in GyM is now focused on the study of the role of roughness and morphology in the sputtering process of W. Ideally placed to support GyM's experiments, different modelling activities have been recently successfully developed with the tokamak plasma edge SOLPS-ITER package [2] and the PMI ERO2.0 code [3]. GyM is contributing to the development of advanced materials, as the ultra-high temperature ceramics, for tokamak plasma-facing components within the Eni-CNR JRA, and it will be used as a testbed for the PMI diagnostics of the divertor tokamak test facility, DTT, like the laser-induced desorption spectroscopy. A huge upgrade of GyM, "BiGyM", is going to take place in the frame of the NEFERTARI project founded by the Next Generation EU, to extend the parameter space toward divertor-relevant plasma densities of 1019 m-3 and ion fluxes of 1023 m-2s-1, and to increase the PMI diagnostic capabilities. This will be achieved by installing a helicon source, a new sample-exposure system and a laserinduced breakdown spectroscopy. The upgrade will allow BiGyM to reach a higher level of competitiveness in the field of PWI and to start brand-new activities in other technological sectors, e.g. aerospace. The progress that has been made towards the release of BiGyM will be here outlined.