Abstract
The Large Helical Device (LHD) is an experimental device for helical type fusion plasma in National Institute for Fusion Science and plasma experiments over 150,000 shots have been successfully conducted during twenty long-term plasma experimental campaigns. The LHD has two kinds of superconducting magnets and nine flexible superconducting bus lines with an average length of 55 m, which are utilized as a part of the current feeder system between the coils and the power sources. The superconducting bus lines consist of a pair of aluminum stabilized NbTi/Cu compacted stranded cable insulated electrically and coaxial five corrugated stainless steel tubes with two layers of vacuum insulations. The nominal current is 32 kA and the withstand voltage is 5 kV in 77 K gas helium. From the first experimental campaign, the superconducting bus lines have been stably operated at steady state by using automatic control. It is also confirmed that the status of the superconducting bus lines are kept good thanks to appropriate maintenances. As the results, the reliable operation of the superconducting bus lines has been achieved during the plasma experimental campaigns without any serious failure and the total operational time of the steady state cooling is approximately 58,000 hours.
Highlights
IntroductionIn many fusion experimental devices, current leads for superconducting magnets are designed to be close to the devices [3,4,5]
The Large Helical Device (LHD), which was completed in 1998, is an experimental device for helical type fusion plasma in National Institute for Fusion Science [1,2]
In the case of the LHD, current leads are located apart from the LHD and close to power sources by utilizing nine flexible superconducting bus lines between the coils and the current leads as a part of the current feeder system in order to expand the space for pumping system, heating devices, diagnostics apparatuses and any other equipment around the LHD
Summary
In many fusion experimental devices, current leads for superconducting magnets are designed to be close to the devices [3,4,5]. The application of the superconducting bus lines leads to reduction of electrical power consumption for the power sources [6]. From the first experimental campaign, the superconducting bus lines have been stably operated at steady state by using automatic control [7]. The reliable operation of the superconducting bus lines has been achieved during the plasma experimental campaigns without any serious failure thanks to optimized operational method and appropriate maintenance between experimental campaigns. The present status of the superconducting bus lines are reported and the operation control method and preventive maintenances for the stable and reliable operation are discussed
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