Ensinger, W.

Floch, E.

Hossain, U. H.

Lima, V.

Seidl, T.

Trautmann, C.

Wietoska, T.

GSI Repository

Dielectric strength of two fiber reinforced plastics irradiated with heavy ions* T. Seidl1,2,#, E. Floch2, V. Lima1,2,U.H. Hossain1,2, T. Wietoska1, C. Trautmann1,2, W. Ensinger11Technische Universität Darmstadt, Germany; 2GSI, Darmstadt, Germany.Glass-fiber reinforced plastics (GFRP) are consideredas structure support and electrical insulator for the newsuperconducting magnets at the Facility for Antiprotonand Ion Research (FAIR). At FAIR, materials close to thebeam tube will be exposed to high doses of secondaryradiation of neutrons, protons, and heavier particles, pos-sibly limiting reliable function and lifetime of devicecomponents. Typical GFRP used in accelerator magnetsconsist of woven glass-fiber fabrics embedded in a ther-mosetting polymer matrix. In superconducting magnetsmost commonly a G11-type composite [1] is used whichconsists of ~60% E-glass-fibers and an amine cured polyepoxy matrix.Radiation hardness studies motivated by the Interna-tional Thermonuclear Experimental Reactor (ITER) showed that neutron-irradiated composites consisting of a cyanate-ester matrix and S-glass fibers exhibit increasedradiation resistance when compared with classical epoxy-systems [2]. In this study a classical G11-type epoxy/E-glass and an ITER-type cyanate-ester/S-glass compositewere irradiated with heavy ions. For the irradiated sam-ples, the dielectric strength (maximum electrical fieldstrength at which the insulator fails) was determined.G11-type epoxy/E-glass (thickness 1.0 mm) and ITER-type cyanate-ester/S-glass (thickness 1.4 mm) compositeswere provided by ISOVOLTA AG (ISOVAL® 11 HKBand cured ISOPREG CN). The G11-type epoxy is acommercially available product whereas the cyanate-ester composite is only available in the form of prepregs and was especially cured by the company for our tests.The irradiation was performed at the Cave A of SIS18with a 400 MeV/u Au-beam and slow extraction mode.The beam spot size was about 0.5 cm2 and the flux of theorder of 108 cm-2s-1. For each material three stacks con-sisting of three samples were irradiated. According to theSRIM-2010 code, the penetration depth of the Au ions isabout 7 mm. The thickness of the sample-stack was 3 mm in case of G11-type and 4.2 mm in case of ITER-typematerial.Breakdown voltage measurements were performed insilicon oil using an AC high voltage tester with roundstainless steel electrodes 15 mm in diameter. The dielec-tric strength was normalized by the thickness and is pre-sented in kV/mm.Figure 1 shows the (AC)-dielectric strength of non-irradiated and irradiated glass-fiber reinforced plastics plotted as a function of irradiation fluence. The dielectricstrength of the cyanate-ester/S-glass system is generally lower than the one of the commercial epoxy system. Forirradiated classical G11-type composite, the dielectric strength decreases as a function of fluence and seems toevolve towards a limiting value of approximately32 kV/mm at higher fluences. In contrast to this, thechange in dielectric strength of irradiated cyanate-ester/S-glass composites is insignificant. Although, the ITER-composite is less affected by degradation, the irradiatedclassical G11 system has still a superior dielectricstrength even at the highest fluence. It needs to be clari-fied whether the initial dielectric strength of the ITER-composite could be raised with an optimized curing pro-cedure.Figure 1: Dielectric strength of G11 and ITER-type plas-tic/glass-fiber composites versus fluence of 400-MeV/uAu ions. Lines are guides to the eye. Earlier studies on ion-irradiated polyimide filmsshowed a drastic decrease of insulating properties at rather low fluences [3]. The effect of ion irradiation forthe analyzed composites is less pronounced probably be-cause of the reinforcement with the inorganic glass-fibers prohibiting the formation of conductive ion tracksthroughout the material.For its usage at FAIR, both investigated compositesshow a tolerable decrease of dielectric strength within thetested range of ion fluences. However, a little caveat be-cause the dielectric strength tests were performed ex-situ at room temperature and not considering low operationtemperatures, thermal cycles or degradation due to dy-namic mechanical forces.[1] National Electrical Manufacturers Association, Stan-dard LI-1, (1998).[2] P.E. Fabian et al., Fusion Engineering and Design61–62 (2002) 795.* Work supported by BMBF, Project No. 06DA90251and 06DA7027.# t.seidl@gsi.de[3] T. Seidl et al., Polymer Degradation and Stability 97(2012) 2396.GSITemplate2007PNI-INHOUSE-EXP-37 GSI SCIENTIFIC REPORT 2012406

Dielectric strength of two fiber reinforced plastics irradiated with heavy ions

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Dielectric strength of two fiber reinforced plastics irradiated with heavy ions

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