Modelling of helium-mediated quench propagation in the LHC prototype test string-1

Abstract

The Large Hadron Collider (LHC) prototype test string-1, hereafter referred to as the string, is composed of three ten-meter long prototype dipole magnets and one six-meter long prototype quadrupole magnet. The magnets are immersed in a pressurized static bath of superfluid helium that is maintained at a pressure of about 1 bar and at a temperature of about 1.9 K. This helium bath constitutes one single hydraulic unit, extending along the 42.5 m of the string length. We have measured the triggering of quenches of the string magnets due to the quenching of a single dipole magnet located at the string's extremity; i.e. "quench propagation". Previously reported measurements enabled to establish that in this configuration the quench propagation is mediated by the helium and not by the inter-magnet busbar connections [1], [2]. We present a model of helium mediated quench propagation based on the qualitative conclusions of these two previous papers, and on additional information gained from a dedicated series of quench propagation measurements that were not previously reported. We will discuss the specific mechanisms and their main parameters involved at different time scales of the propagation process, and apply the model to make quantitative predictions. The Large Hadron Collider (LHC) prototype test string-1, hereafter referred to as the string, is composed of three ten-meter long prototype dipole magnets and one sixmeter long prototype quadrupole magnet. The magnets are immersed in a pressurized static bath of superfluid helium that is maintained at a pressure of about 1 bar and at a temperature of about 1.9 K. This helium bath constitutes one single hydraulic unit, extending along the 42.5 m of the string length. We have measured the triggering of quenches of the string magnets due to the quenching of a single dipole magnet located at the string's extremity; i.e. "quench propagation". Previously reported measurements enabled to establish that in this configuration the quench propagation is mediated by the helium and not by the inter-magnet busbar connections [1], [2]. We present a model of helium mediated quench propagation based on the qualitative conclusions of these two previous papers, and on additional information gained from a dedicated series of quench propagation measurements that were not previously reported. We will discuss the specific mechanisms and their main parameters involved at different time scales of the propagation process, and apply the model to make quantitative predictions.

Flower, a model for the analysis of hydraulic networks and processes

“…The heating waveform for the volume k associated with a quenching magnet was taken as: . Equation (30) has resemblance to the measured power deposition profiles reported in [12] and [13] and the coefficients have been obtained fitting the curves reported there. Note that during a quench only a small part of the magnetic energy is deposited in the helium, while a large portion is stored in the thermal capacity of the cold mass.…”

“…The transition of the whole cold mass from superfluid to normal helium has been taken to indicate the arrival of the normal fluid front from the neighbouring, quenching magnet. This is associated in reality with a sharp temperature increase that was properly considered in [13], but is not modelled accurately by the simple model used for the demonstration calculation discussed here.…”

“…To identify the modelling elements for the simulation of the LHC String 2 we have followed the approach described in [12] and [13]. Each magnet has been modelled as two volumes, of which the first represents the helium in intimate contact with the superconducting coil, heated during a quench, while the second volume represents the rest of the helium contained in the cold mass, between the iron laminations, in the end-caps and in the internal pipings.…”

“…Each magnet has been modelled as two volumes, of which the first represents the helium in intimate contact with the superconducting coil, heated during a quench, while the second volume represents the rest of the helium contained in the cold mass, between the iron laminations, in the end-caps and in the internal pipings. This is a much simplified version of the model described in [13], where in addition the presence and size of helium buffer volumes at the magnet endcaps as well as the time dependent temperature margin of the superconducting coil were modelled in a much greater detail.…”