High Current Diffusion Type Diodes at Cryogenic Temperatures for the LHC Superconducting Magnet Protection

Abstract

High-current by-pass diodes are required for the protection of the superconducting magnets for the Large Hadron Collider LHC at CERN. These diodes are at liquid helium temperature and will be exposed to irradiation. With the re-location of the by-pass diodes for the main dipoles underneath the iron yoke, and of those for the quadrupoles at the bottom of the cryostat the new estimations for the irradiation dose amounts to about 30 Gy with a neutron fluence of about 1.5 × 10¹¹ n/cm² for the dipole diodes, and about 100 Gy and 5 × 10¹¹ n/cm² for the quadrupole diodes over 10 years. These relatively low doses may allow the use of diffusion type diodes instead of epitaxial diodes. The electrical characteristics of several diodes were measured at temperatures in the range between 1.8 K and 300 K. Diffusion type diodes from three manufacturers were submitted to high current endurance tests in liquid helium. Electrical characteristics and temperatures were measured versus time and showed acceptable results. First irradiation tests show that modified diffusion diodes can be used at least for the dipole by-pass.