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For the protection of the LHC superconducting magnets, about 2100 specially developed by-pass diodes were manufactured by DYNEX SEMICONDUCTOR LTD (Lincoln, GB) and about 1300 of these diodes were mounted into diode stacks and submitted to tests at cryogenic temperatures. To date about 800 dipole diode stacks and about 250 quadrupole diode stacks for the protection of the superconducting lattice dipole and lattice quadrupole magnets have been assembled at OCEM (Bologna,Italy) and successfully tested in liquid helium at ENEA (Frascati, Italy). This report gives an overview of the test results obtained so far. After a short description of the test installations and test procedures, a statistical analysis is presented for test data during diode production as well as for the performance of the diode stacks during testing in liquid helium, including failure rates and degradation of the diodes. CRYOGENIC TESTING OF HIGH CURRENT BY-PASS DIODE STACKS FOR THE PROTECTION OF THE SUPERCONDUCTING MAGNETS IN THE LHC ABSTRACTFor the protection of the LHC superconducting magnets, about 2100 specially developed by-pass diodes were manufactured by DYNEX SEMICONDUCTOR LTD (Lincoln, GB) and about 1300 of these diodes were mounted into diode stacks and submitted to tests at cryogenic temperatures. To date about 800 dipole diode stacks and about 250 quadrupole diode stacks for the protection of the superconducting lattice dipole and lattice quadrupole magnets have been assembled at OCEM (Bologna,Italy) and successfully tested in liquid helium at ENEA (Frascati, Italy). This report gives an overview of the test results obtained so far. After a short description of the test installations and test procedures, a statistical analysis is presented for test data during diode production as well as for the performance of the diode stacks during testing in liquid helium, including failure rates and degradation of the diodes.

The superconducting sagnets for ISA3ELLE-Jill use a forced flow supercritical helium cooling system. In order :a evaluate this cool ins scheme cwo Individual dipole magnets ware first tested in conventional dewars using pool soiling heliua. These sagnecs were then modified for forced flow cooling and receescd wich che idencictl signae coils. Ine fir« (valuation cesc used lU long ISA model dipole magnet whose pool builing performance had been esubllshcd. 5>.e sasa magnet, was cheo reeested with forced flow cooling, energising ic at various operacing temperatures until quench occurred. The magnet's performance wish forced flow cooling was consistent with data from the previous pool boiling casts. The next step in the program was a fall-scale ISA3ELLE dipote ring nagnat, 4.25 a long, whose perfaroance was first evaluated with pool boiling. For che forced flow test she nagnec was shrunk-fit into an unsplic laainatad core encased in a stainless steel cylinder. The high pressure gas is cooled below 4 X by a helium bath which is pumped below atmospheric pressure with an ejector nozzle. The performance of the full-scale dipole magnet in the new configuration with farced flow cooling, showed a 102 increase in the atcainable maximm currsne as compared Co she pool boiling data.

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