Speaker
Description
The recent commissioning of the 36 T Series-Connected Hybrid Magnet at the National High Magnetic Field Laboratory has uncovered an undesirable consequence of using super critical helium for cooling of superconductors. This new “dry-magnet” cooling technology greatly reduces the LHe requirements of the magnet and may be utilized more frequently in the future. Because the supercritical helium does not complete a phase transition with the addition of heat, the fluid can quickly expand. The increased expansivity of supercritical helium over liquid helium for a given heat load is capable of creating larger pressure waves. The impact pressure for compressible helium gas flow is combined with the speed of sound for ideal gases to determine if a high speed pressure wave is sufficient to explain the premature failure of the burst discs in the over-pressurization protection system. The addition of an impact pressure can explain, under the right conditions, an up to 40% reduction in the burst disc pressure rating. The venting response time is discussed and a comparison of using voltage and pressure quench detection is made. Pressure oscillations in the readings are quantified in order to avoid unnecessary quench detections.
