Analysis of the quench propagation along Nb3Sn Rutherford cables with the THELMA code. Part II: Model predictions and comparison with experimental results

Abstract

a b s t r a c tTo improve the technology of the new generation of accelerator magnets, prototypes are being manufactured and tested in several laboratories. In parallel, many numerical analyses are being carried out to predict the magnets behaviour and interpret the experimental results. This paper focuses on the quench propagation velocity, which is a crucial parameter as regards the energy dissipation along the magnet conductor. The THELMA code, originally developed for cable-in-conduit conductors for fusion magnets, has been used to study such quench propagation. To this purpose, new code modules have been added to describe the Rutherford cable geometry, the material non-linear thermal properties and to describe the thermal conduction problem in transient regime. THELMA can describe the Rutherford cable at the strand level, modelling both the electrical and thermal contact resistances between strands and enabling the analysis of the effects of local hot spots and quench heaters. This paper describes the model application to a sample of Short Model Coil tested at CERN: a comparison is made between the experimental results and the model prediction, showing a good agreement. A comparison is also made with the prediction of the most common analytical models, which give large inaccuracies when dealing with low n-index cables like Nb 3 Sn cables.

Quench dynamics in MgB2Rutherford cables

“…There are some aspects to consider in the analysis of the experimental estimations of v p . Ideally, it is preferable to estimate quench propagation velocities farther away from the heater, which is even more relevant in Rutherford cables, as during the first stages of quench development different velocities can be obtained from different individual strands [21] [27]. Nevertheless, in real experiments if longer distances from the heater are sensed to estimate v p , the temperature of the hot-spot may also increase considerably depending on the sheath properties, and may cause the irreversible damage of the cable.…”

“…In the cables analysed in this study, the predictions given by Wilson and Dresner show rather good agreement with the experimental values. It is worth noting that despite of the simplifying assumptions of these models, they give valuable estimations of propagation velocities, at least as first approximations, not only for wires and tapes [23] but also for cables [27]. For example, recent studies by Manfreda et al [27] in quench propagation along Nb 3 Sn Rutherford cables concluded that predictions by Wilson's and Dresner's analytical models give close approximations, although they tend to overestimate the experimental values, mainly at lower temperatures (1.9 K), whereas at 4.2 K they give more accurate predictions, especially when using Dresner's equation.…”

Effect of Strand Damage in Nb3Sn Rutherford Cables on the Quench Propagation in Accelerator Magnets

“…Several models have been used to study the quench behavior of Rutherford-type cable structures in the past. Notably, the CUDI model has been used to study their thermal stability [7,8,9] and the THELMA model was used to study quench propagation [10,11].…”

Quench Propagation in Nb<inline-formula> <tex-math notation="LaTeX">$_\text{3}$</tex-math> </inline-formula>Sn Cos-Theta 11 T Dipole Model Magnets in High Stress Areas

“…During the test of the last dipole (SP 105) a high quench propagation velocity (QPV) was observed for quenches originating in the magnet's midplane, the area where the stress is larger and the magnetic field gradient is maximum. Quench propagation on Nb 3 Sn Rutherford cables has been studied and modeled before [6], [7], [8], but for configurations without a magnetic field gradient across the width of the cable. This motivated an investigation on the quench propagation of quenches in all the 11 T model magnets.…”