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ENEA - Fusion division

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Power Diodes and Current Leads

Contact: Simonetta Turtù
e-mail: simonetta.turtu@enea.it
tel.: +39 06 9400 5396
fax.: +39 06 9400 5393
By-pass diode stacks of Large Hadron Collider (CERN)By-pass diode stacks for dipole magnets (left) and
quadrupole magnets (right) of the Large
Hadron Collider (CERN)

The Superconductivity section hosted in its laboratories the activities of OCEM (a leading Italian company engaged in the product of electronic devices and power supplies) aimed at testing the by-pass diodes (see photo) to be installed to protect the about 8000 superconducting magnets of the Large Hadron Collider (LHC) being built at CERN.
The work consisted in testing the diodes under “endurance” cycles at liquid helium temperature. During the tests a current pulse (Imax = 14 kA) was applied to simulate the magnet discharge that the diodes have to by-pass when in operation.

Our group was responsible for organising and supervising the cryogenic tests requested by CERN.

Thanks to the available competence and apparatus in the fields of superconductivity and cryogenics and to the positive collaboration during the tests on the pin diodes, CERN has also decided to assign to the ENEA Superconductivity Section, the final testing of part of the HTS current leads for LHC magnets power supplies.
Current leads represent the electric link between the power supplies terminations, at room-temperature, and the superconducting connections to the magnets, at 1.8K. Therefore such devices have to work with an elevate temperature gradient (300K-1.8K) and depending on the type of magnet which will be alimented, at currents between 600A and 13000A.
In the operative phase, 1000 leads will be necessary.
The cryogenic test of these devices is the object of the contract stipulated between CERN and ENEA.

The test consists, once the temperature gradient has been created along the leads, in feeding them at the nominal operative current and let it flow an hour long, making sure that the parameters indicating the right functioning (mainly the voltage drop along their resistive part and the temperature of the superconducting section) remain under safety limits.

Coppia di Discendenti da 6KAcouple of 6kA leads
installed and ready for
stazione di collaudo criogenico dei DiscendentiENEA experimental station for the cryogenic test of the leads.

In 2004, our group has designed and realized the full experimental system for these tests, following the typical standards of a scientific experiment, but at a rate of industrial production, considering the great number of devices which need to be tested.
The experimental campaign began in January 2006 and ended in January 2007, respecting the CERN requirements.