Length change of organic insulators after reactor irradiation at 5 K

The length change in organic insulators, fibre reinforced plastic (FRP) with glass-cloth laminates, for superconducting magnets for fusion reactors was measured after reactor irradiation at 5 K. The annealing behavior was also studied in the temperature range of 10 to 320 K. Measurements of the length change were carried out by change in capacitance using an ac ratio bridge. The fractional change of the length induced by the irradiation Δlsub(irrad)/l0, was found to be 0.3-2.3 x 10-3 for a dose of 4.5 x 106 Gy. These values are about 5-36 times the elongation of pure Al after reactor irradiation at 5 K. This is important data for the fabrication of the superconducting magnets because Al and Cu are used as stabilizer material in the magnet. Particular attention should be paid to the reverse recovery along the direction perpendicular to the axis of VL-H208 which was observed above 200 K. (orig.)