Irradiation of Bypass Diodes up to 2.2E14 Neutron/cm2 and 1.3 kGy for the FAIR Project

The FAIR project planned at G.S.I. (Germany) requires the construction of several superconducting accelerator rings. One of the two synchrotron rings, named SIS300, will have dipoles with a central field of 6 T and a ramp rate of 1 T/s. In order to protect these fast-ramping magnets in case of a quench, each of them must be equipped with a diode stack that bypasses the magnet in case it quenches. In order to save time and money on R&D, we decided to use the same diode type as that mounted in LHC magnets. These diodes were previously tested at 77 K up to a fast neutron fluence (F) of 2.8E13 n/cm² and a dose (D) of 2 kGy which are the expected radiation loads after 20 years of LHC operation. Having no definitive estimation of the losses in the SIS300, we arbitrarily targeted a fluence of 1E14 n/cm². We irradiated six LHC type diodes at 77 K in six steps. The highest values measured were 1.31 kGy and 2.25E14 n/cm². Before and after each irradiation step, the forward and reverse voltage characteristics of each diode were measured. This paper reports the results of these measurements, carried out at ITEP (Moscow).