Stability Analysis of the LHC Cables for Transient Heat Depositions

Abstract

Abstract-The commissioning and the exploitation of the LHC require a good knowledge of the stability margins of the superconducting magnets with respect to beam induced heat depositions. Previous studies showed that simple numerical models are suitable to carry out stability calculations of multi-strands cables, and highlighted the relevance of the heat transfer model with the surrounding helium. In this paper we present a systematic scan of the stability margin of all types of LHC cables working at 1.9 K against transient heat depositions. We specifically discuss the dependence of the stability margin on the parameters of the model, which provide an estimate of the uncertainty of the values quoted. The stability margin calculations have been performed using a zero-dimensional (0-D) numerical model, and a cooling model taking into account the relevant helium phases which may appear during a stability experiment: it includes Kapitza thermal resistance in superfluid He, boundary layer formation and heat transfer in He I, and considers the transition from nucleating boiling to film boiling during He gas formation.

Beam losses from ultraperipheral nuclear collisions betweenPb82+208ions in the Large Hadron Collider and their alleviation

“…9) consist of strands (28 and 36 in the inner and outer windings, respectively), made of NbTi filaments, which are embedded in a copper matrix. Helium inside the cables occupies the space between the strands [31] but serves mainly to increase the heat capacity for protection against transient losses [32]. The cables are wrapped with three layers of polyimide electric insulation and a 0.5 mmthick ground electric insulation is placed between the coil and the collar, which has been identified from measurements as a heat reservoir [33].…”

“…The network model simulations show that the temperature margin at this average heat load is 0.3 K. We consider three time scales as in Ref. [32].…”

Modeling of Quench Limit for Steady State Heat Deposits in LHC Magnets

“…In this paper only steady-state conditions are considered, the transient conditions are the subject of the other paper presented to this conference [7].…”

Deduction of Steady-State Cable Quench Limits for Various Electrical Insulation Schemes With Application to LHC and HL-LHC Magnets

“…However, it must be noticed that the power deposited in the coil during the quench test was near steadystate. Numerical studies suggest that the quench limit in such conditions should be higher than the steady-state value [6] [7]. Table I summarizes the quench limit values for MB and MQXF in the most significant current and future operating conditions, obtained with the assumptions reported in the paper.…”