Superconducting magnets of future particle accelerators like FCC will be exposed to high radiation doses, and polymers are the magnet constituent materials most sensitive to irradiation effects. Polymers are for instance needed for dielectric insulation, and for the impregnation of superconducting magnet coils made of brittle conductors like Nb3Sn.
To qualify polymer materials for potential use in future superconducting accelerator magnets, the CERN polymer laboratory is performing an irradiation study. The main goals of the first stage of this study are to determine the effect of different radiation sources, of different radiation atmospheres and temperatures on the functional materials properties. Irradiations are performed with:
• 24 GeV protons with the CERN PS beam in collaboration with the IRRAD and Cryolab teams
• Neutron irradiations at the research reactor of TU Vienna and with the NEAR n-ToF spallation source at CERN
• 60Co gamma irradiations at the Gammatec facility of the company Steris.
To assess the aging processes and to determine aging rates we apply Dynamical Mechanical Analysis (DMA). DMA storage and loss moduli evolutions reveal the effect of the competing influence of cross linking and chain scission on the glass transition temperature (Tg). The DMA measurements are complemented by different static and dynamic mechanical tests and outgassing measurements.
We describe the aging under irradiation with different sources of epoxy resin systems that can be used for the vacuum impregnation of magnet coils. Aging rates for these resin systems in ambient air up to a dose of 30 MGy have been determined.
Since the polymers in superconducting magnets are irradiated at cryogenic temperature in the absence of oxygen, we study the effect of the irradiation temperature and environment. At the CERN IRRAD facility we have irradiated the same epoxy resins with a 24 GeV proton beam in four different environments:
• In ambient air at 20 °C
• In inert gas at 20 °C
• In dry air at minus 20 °C
• Immersed in liquid helium at 4.2 K
The first test results show that the irradiation environment can substantially impact the irradiation induced aging of epoxy resins. Future irradiation plans will be proposed.
References
[1] Gaarud A.; Parragh D.M.; Clement S.; Scheuerlein C.; Piccin R.; Lach R.; “Improved fracture toughness at cryogenic temperature of irradiation hard epoxy system for superconducting coil impregnation”, ( http://ssrn.com/abstract=4478135 )
[2] Parragh, D. M.; Scheuerlein, C.; Piccin, R.; Ravotti, F.; Pezzullo, G.; Ternova, D.; Taborelli, M.; Lehner, M.; Eisterer, M., “Irradiation induced aging of epoxy resins for impregnation of superconducting magnet coils”, submitted to IEEE Trans. Appl. Supercond.
[3] C. Scheuerlein, presentation at KE4738 collaboration meeting N°16, 17th November 2022
Effect of irradiation source and environment on thermomechanical properties of polymers for accelerator magnets (cern.ch)