Ramp rate induced quenches in the one-metre dipole model magnets for the CERN LHC

During the investigation of 1 m model dipoles for the Large Hadron Collider (LHC) a considerable number of quenches are performed at high ramp rate. In this paper the results are presented of these quenches which are made both at 1.7-2.1 K and at 4.3 K for ramp rates varying between 10 As/sup -1/ and 300 As/sup -1/. The quench current is strongly affected by the inter-strand coupling currents and the heat due to these currents. Furthermore, the influence of a current precycle is considered which can result in a significant increase of the quench current (at the same ramp rate). It is shown that this increase can be attributed to the presence of so called "super coupling currents" which strongly influence the current distribution among the strands, exhibiting characteristic time in the order of a few hundred to a few thousand seconds. Generally, the origin of the ramp rate induced quenches is close to the midplane of the inner coil of the magnet, where the field perpendicular to the wide side of the cable is maximum.<>