First Experimental Results on Damage Limits of Superconducting Accelerator Magnet Components Due to Instantaneous Beam Impact

Abstract

The energy stored in the particle beams of an accelerator such as CERNs LHC is substantial and requires a complex machine protection system to protect the equipment from damage. Despite efficient beam absorbers, several failure modes can lead to beam impact on superconducting magnets. The energy deposition from these beam losses can cause significant temperature rise and mechanical stress in the magnet coils, which can lead to a degradation of the insulation strength and critical current of the superconducting cables. An improved understanding of the damage mechanisms is important for the LHC when considering its planned increase in beam brightness, as well as for other accelerators using superconducting magnets. The degradation mechanisms of Nb-Ti and Nb $_3$ Sn strands and the cable stacks insulation have been assessed based on magnetization and breakdown voltage measurements in three experiments at room temperature. The degradation of the insulation when exposed to high temperatures for several hours was measured. The second experiment assessed the effect of a millisecond temperature rise on superconducting strands using a fast capacitor discharge. In the third experiment, cable stacks and single strands have been exposed to a 440 GeV proton beam. In this paper, the experimental results of these tests are presented and discussed.