Quench Heater Studies for the LHC Magnets

About 2000 LHC (CERN's Large Hadron Collider) superconducting magnets will be protected with quench heaters against development of excessive voltage and overheating after a resistive transition. The quench heater strips are powered by capacitor bank discharge power supplies. The strips are made of stainless steel partially plated with copper to reduce their resistance and to allow for the connection of quench heaters in series. The strips are embedded in between two polyimide foils. The initial power density and the current decay time determine the quench heater effectiveness. Since only one type of heater power supply will be available, the copper plating cycle is adapted for the various magnet types to keep the resistance of the heater circuit constant. Different quench heater designs have been tested on various prototype magnets to optimise the copper-plating cycle and the electric insulation of the heater strip. This paper summarises the experimental results and computations that allowed to finalise the heater strip layout for all LHC magnets

Radiation Tolerance of Components Used in the Protection System of LHC Superconducting Elements

A selection of electronic devices to be used for the protection of superconducting elements of the Large Hadron Collider LHC has been submitted to functional tests in the CERN TCC2 irradiation test facility. The results confirm the validity of the various designs, which are entirely based on COTS (Components-Off-The-Shelf)

Detection of Resistive Transitions in LHC Superconducting Components

The LHC has entered the construction phase. It will incorporate a large number of superconducting components like magnets, current leads and busbars. All these components require protection means in case of a transition from the superconducting to the resistive state, the so-called quench. Key elements in the protection system are electronic quench detectors, which have to be able to identify a quench in any state of the powering cycle of the accelerator. According to the different properties and characteristics of the superconducting elements and circuits, a set of quench detectors adapted to their specific tasks has been developed

On the exceptional set in Nevanlinna's second fundamental theorem in the unit disc

A general example of an analytic function in the unit disc possessing an exceptional set in Nevanlinna's second fundamental theorem is built. It is used to show that some conditions on the size of the exceptional set are sharp, extending analogous results for meromorphic functions in the plane

Protection of LHC superconducting corrector magnets

The protection of superconducting magnets in case of a quench has to be considered already in the design phase for the proton-proton collider LHC. The protection of main dipole and quadrupole magnets, based on cold diodes and quench heaters, is reported elsewhere [1]. In this paper the protection of other magnets is discussed. In the arcs some of the magnets are connected in series: sextupole magnets to correct the lattice chromaticity, small sextupole and decapole magnets to correct systematic field errors of the dipoles and octupole magnets. The magnets in the arcs to correct horizontal and vertical closed orbit excursions are powered individually. In the insertions other superconducting magnets will be used: quadrupole magnets for the low-beta insertions, orbit corrector magnets, etc. Some magnets will be constructed with sufficient copper stabilization to safely absorb the energy. For other magnets different methods of protection after the detection of a quench in the circuit are envisaged

Proposed Method for the Verification of the LHC Bus Bar Splices during Commissioning at Cryogenic Conditions

The commissioning of the Large Hadron Collider at CERN includes the powering of about 1600 superconducting electrical circuits to currents ranging from 55 A to 11.8 kA. A large number of splices (over 70'000) are present at the magnet interconnects, which can only be validated with current at cryogenic conditions. This paper discusses the thermal effects related to possible faulty splices during the powering of the circuits. The calculations of the quench and detection currents, as well as the hot spot temperatures, are described. The heat transfer model with the surrounding coolant and the current profiles inside the splices are presented. This study is completed with a sensitivity analysis on the hot spot temperature with respect to the model parameters. Finally, the implications with respect to the powering ramps and parameters to be applied during the first powering are discussed