13th International Conference on Magnet Technology (MT13), Victoria, Canada electrically separated units which has important advantages. resistors in series with the magnets. The LHC main ring magnet will be divided into 16 over-heating the by-pass diode. This is done by switching high-power energy-dump chain must be de-excited rapidly to avoid spreading the quench to other magnets and quench out more quickly over a large volume of the magnet. After a quench the magnet necessary to detect quickly the incipient quench and tire strip heaters which spread the heating of the zone where the quench started and to high intemal voltages. It is therefore slow propagation speed of a "natural" quench (10 to 20 m/s) can lead to excessive The high energy density of the LHC magnets (500 kJ/m) coupled with the relatively diodes are exposed to some 50 kGray of radiation during a 10 year operation life-time.diodes situated inside the cryostat as by-pass elements -so-called cold diodes. The de-exciting the unquenched magnets. For the LHC machine it is foreseen to use silicon destroying it. This is avoided by by-passing the quenched magnet and then rapidly magnetic energy of all the magnets will be dissipated in the quenched magnet so concept. In a group of series connected magnets if one magnet quenches then the Hadron Collider (LHC) is described. The system is based on the so-called "cold diode"The quench protection system for the superconducting magnets of the CERN Large

The protection system for the superconducting elements of the Large Hadron Collider (LHC) [1] at the European Laboratory for Particle Physics (CERN), and its associated equipment are presented: quench detectors, cold diodes, quench heaters and related power supplies, extraction resistors and associated current breakers. Features such as radiation resistance, redundancy and required reliability are discussed.

A.strirct-?'h c J-I'A KC Neu trin o Ex pcri nicn t. tli e construction of which starts in JFY 2004, will use a superconducting niagnct system for its primary proton beam linc. The system, which bends the SO GeV 0.75 hl\V proton b a r n by about .80 degrees, consists of 25 superconducting coni bincd function magnets. The magnets utilize single layer leftlright asyinmetric coils that generate a dipoIe field of 2.6 T and a quadrupole field of 18.6 T/m with the operation current of about 7.35 kA. The system also contains a few conduction cooled superconducting corrector magnets that serve as vertical and horizontal steering magnets. All the magnets are designed to provide a physical beam aperture of 130 mm in order to achieve a large beam acceptance. Extensive care is also required to achieve safe operation with the high power proton beam. The paper summarizes the system design as well as some safety analysis results. I t z d a Terms-Accelerato r safety, Neutrinos, P a r t i c l e beam t r a n s p o r t , S u p e r c o n d u c t i n g accelerator magnets, I. INTRODUCTION HE Tokai-to-Kaniioka Neutrino experiment (T2K) [1][2] is T a nest generation neutrino oscillation experiment. The Manuscript recei! ed October 5.2004 This \vork \\-as supported in part by the JSPS US-Japan collaboration program Toru Ogitsu,

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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.