Plasma position reflectometry (PPR) is a microwave radar technique that aims to provide information on the plasma column position and shape by monitoring the edge density profiles at several poloidal positions in Tokamaks. The PPR in-vessel diagnostic equipment is compact, non-invasive and intrinsically resistant to neutron radiation. For this reason, after some initial tests on ASDEX-Upgrade, a partial PPR system is being designed on DTT in view of DEMO, where long pulses and high neutron fluxes are likely to jeopardize the long-term reliability of the internal magnetic sensors. On RFX-mod2 (R=2.0 m, a=0.49 m), the upgraded version of the previous RFX-mod device, a simplified PPR scheme, consisting of four bistatic reflectometric units, has been conceived to test some of the issues related to a plasma position control on a fusion reactor. However, its integration in the machine had required different innovative solutions. This contribution is focused on the technological aspects linked, in particular, to the installation of the antenna pair and the waveguide system in the high field side section of RFX-mod2. Waveguides, insulated through the application of a ZrO painting, will be routed in between the vacuum vessel and the conductive shell to a vertical port. The severe constraints in terms of physical space available guided the antennas design: a hoghorn antenna model was first numerically modeled and, due to the complex geometry, produced through metal additive manufacturing; then, a post-production surface treatment allowed achieving a surface with characteristic roughness and conductivity comparable to traditional manufactured antennas. A bench-test is finally carried out to assess the overall system performance. Peculiar issues, being faced for PPR high field side subsystem on larger fusion devices, are finally briefly reviewed in light of the experience gained during this specific realization.
Technology challenges and integration of the plasma position reflectometer in RFX-mod2
De Masi G;Marchiori G;Peruzzo S
2023
Abstract
Plasma position reflectometry (PPR) is a microwave radar technique that aims to provide information on the plasma column position and shape by monitoring the edge density profiles at several poloidal positions in Tokamaks. The PPR in-vessel diagnostic equipment is compact, non-invasive and intrinsically resistant to neutron radiation. For this reason, after some initial tests on ASDEX-Upgrade, a partial PPR system is being designed on DTT in view of DEMO, where long pulses and high neutron fluxes are likely to jeopardize the long-term reliability of the internal magnetic sensors. On RFX-mod2 (R=2.0 m, a=0.49 m), the upgraded version of the previous RFX-mod device, a simplified PPR scheme, consisting of four bistatic reflectometric units, has been conceived to test some of the issues related to a plasma position control on a fusion reactor. However, its integration in the machine had required different innovative solutions. This contribution is focused on the technological aspects linked, in particular, to the installation of the antenna pair and the waveguide system in the high field side section of RFX-mod2. Waveguides, insulated through the application of a ZrO painting, will be routed in between the vacuum vessel and the conductive shell to a vertical port. The severe constraints in terms of physical space available guided the antennas design: a hoghorn antenna model was first numerically modeled and, due to the complex geometry, produced through metal additive manufacturing; then, a post-production surface treatment allowed achieving a surface with characteristic roughness and conductivity comparable to traditional manufactured antennas. A bench-test is finally carried out to assess the overall system performance. Peculiar issues, being faced for PPR high field side subsystem on larger fusion devices, are finally briefly reviewed in light of the experience gained during this specific realization.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
