Quench characteristics of 5-cm-aperture, 15-m-long SSC dipole magnet prototypes

Abstract

The quench performance and ramp rate sensitivity of eighteen 5-cm-aperture, 15-m-long SSC dipole magnet prototypes are discussed. All the magnets appear to reach a quench plateau near their extrapolated short sample current limit and well in excess of the operating current with very little training. Most of the magnets, however, exhibit a dramatic degradation of their quench current as a function of ramp rate, which for the most part, can be attributed to large cable eddy currents.

Influence of Inter-Strand Electrical and Thermal Conductivity on Stability of Rutherford Cables in Accelerator Magnets

“…2(a) of [2] can be explained in the following way using results of combinations A and B: though the current distribution is nonuniform due to the existence of "supercurrents", the MQE did not drop to very low lever. Therefore, magnets' quench currents decrease with the increase of ramp rate mainly due to the increase of AC losses.…”

“…It is reported that for a low ramp rate (e.g., 1 A/s), quench of SSC dipole magnet prototypes generally originated at the coil end, whereas for a high ramp rate, quench origin moves to the middle plane of coil inner layer [2]. On the middle plane of coil inner layer, the magnetic field is more perpendicular to the wider face of Rutherford cable.…”

“…Time constant of "supercurrents" (or so-called super-coupling currents) in Rutherford cables for accelerator magnets is of the order of seconds, which is several times larger than the operating cycle time of SSC High Energy Booster [2]. Therefore, it is reasonable to assume that the coupling current is approximately proportional to the magnetic field of the magnet, and therefore proportional to the magnet current, i.e., (7), in the following calculations, for a given point in a given magnet, the current nonuniformity ratio is taken as a constant during ramping-up and down of magnet current.…”

“…The magnetic diffusivity of the electromagnetic process can be written as (2) where is the inductance per unit length of the loop formed by two strands and is the inter-strand electrical conductivity. Therefore, the cable length in the simulation model should be several times larger than .…”

“…was found. For instance, the RRL curves of SSC dipole magnet prototypes can be divided into two evidently different types [2]. This is an important issue in particular for magnets for SSC High Energy Booster, as the nominal ramp rate of SSC High Energy Booster is relatively high.…”