Septum magnet MNP-23 for the CERN PS experimental area and its fast interlock system

Two MNP-23 septum-like magnets are installed at CERN in the transfer line from the Proton Synchrotron (PS) to the East Hall Experimental Area. They are exposed to extremely high doses of ionizing radiation. In the past, the magnets experienced two catastrophic failures due to overheating of its coils and cannot be repaired. The magnets of improved design which is subject of this article are built as replacements for the magnets presently installed. The MNP-23 is a resistive C shaped iron-dominated magnet made of solid low carbon steel blocks. The excitation windings consist of two water-cooled coils wound from hollow copper conductor. The septum design of these magnets implies a high current density which requires an efficient water cooling system. The newly designed cooling circuit provides better cooling performance and more reliability. To avoid failures due to coil overheating, an elaborate interlock system was developed and installed. It consists of two parts: firstly a slow, more classic sensor, to detect gradual water blockages and inlet cooling water temperature rises and secondly a fast response device to detect sudden loss of water cooling due to external leaks or sudden blockage of one of the water cooling circuits in the coil. The article outlines the unusual and challenging design of the magnet and its interlock system and describes the hardware as well as its performance.