Abstract
Nb3Sn superconducting magnets represent a technology enabler for future high-energy particle accelerators. A possible impediment, though, comes from flux jumps that, so far, could not be avoided by design unlike for NbTi technology. However, the impact of flux jumps on the magnet powering has not been properly investigated to date. Flux jumps appear during current ramps at relatively low value of current and tend to disappear towards nominal current. They are usually detected as voltage jumps between different magnet coils but they might also produce overall voltage jumps across the magnet electrical terminals. Such jumps might perturb the power converter feedback control loop and therefore potentially jeopardize its precision performance during energy ramps. This work aims at: (i) presenting preliminary experimental test results on some HL-LHC Nb3Sn model and prototype magnets, and (ii) attempting to build a simplified electrical model of the flux jumps, with focus only at its interaction with the power converter feedback control loop. Such a work is a starting point for outlining possible power converters control strategies able to minimize flux jumps impact on high-precision powering of Nb3 Sn superconducting magnets.
Highlights
Nb3Sn superconducting magnets represent a technology enabler for future high-energy particle accelerators
Quench protection systems must be able to discriminate them from quench events, the impact of flux jumps on the powering has not been properly investigated to date so no available models can be used for its estimation
No attempt will be made at investigating their amplitude and frequency of occurrence as a function of the current level, because this does not really matters for the powering even though it is very relevant for quench protection systems that can exploit, as an example, the dependence of flux jumps amplitude on the current level to adapt the quench detection thresholds as current is ramping up
Summary
Nb3Sn superconducting magnets represent a technology enabler for future high-energy particle accelerators. At the time instants tk (when the Bernoulli random generator simulates a jump happening) the inductance (of a single coil i j of the magnet) suddenly decreases (in a time Ts) by a random amount dLkij and recovers with a longer time constant (to reproduce what is observed experimentally) which is assumed to be a random variable (RV) The amplitude of the jumps is normalized to the current value in order not to produce larger flux jumps at increasing current This is a rather strong assumption; it is deemed sufficient for the scope of this work to be able to simulate the effect of the phenomenon on the current regulation operated by the power converters.
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