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Influence of the flow imbalance among the cooling channel on the magnet performance
Hyunjung Lee(이현정),Chu Young(추용),Jinsub Kim(김진섭) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
Cryogenic circuit for cooling of a superconducting magnet like tokamak has a lot of branch and has to be designed efficiently considering the conductance for cooling. The KSTAR PF cryogenic circuit has one hundred eight cooling paths for fourteen superconducting magnets and CS structure. The five cryogenic valves has been installed to provide the same mass flow rate to cooling channel of magnet. The individual flow imbalance test has been performed one of the manufacturing process and it was below 10 %. But, we knew that the flow imbalance increased during magnets operation by installed of 10 mass flow rate meters in front of magnets additionally. In this paper, this flow imbalance will be applied to the KSTAR PF circuit modeling, which has been developed using SUPERMAGNET code, and the effect will be compared with the experiment data.
Hyunjung Lee(이현정),Jinsub Kim(김진섭),Chu Young(추용),Kwang Pyo Kim(김광표),Kabrai Park(박갑래) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
A cryogenic circuit for large scaled superconducting device like a tokamak is installed quite complex. In the KSTAR tokamak, the five cryogenic circuits are managed for cooling of each components (Toroidal Field magnets, Poloidal Field magnets, structures current leads, thermal shield, buslines) independently. The circuit for the Poloidal Field magnets branches into one hundred cooling channels. Five cryogenic valves are controlling the flow rates according to cooling channel length. The KSTAR PF1 upper and lower magnets have ten cooling channels parallel respectively. The pressure drop of the magnets is adjusted by cryogenic valve and is maintained by a supercritical helium circulator. The flow rate should be uniform among the cooling channels or magnets but the flow imbalance was observed during the flow test of magnet individually. The measured imbalance was around 10 % between KSTAR PF1 upper and lower. To investigate for effect of the flow imbalance on the magnet, the simple model of the PF1 upper and lower magnets has been developed using SUPERMAGNET code. The maximum temperature trends are studied in details depending on the imbalance.
이현정(Hyunjung Lee),김현욱(Hyunwook Kim),권기일(G. K. Kwon),추용(Young Chu),김광표(K. P. Kim),박갑래(K. R. Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
The KSTAR superconducting coil has been operated for more than a decade since 2007, and analysis of AC losses characteristics of superconducting magnet experiments have been conducted annually for safety and estimate of life. A total of 30 superconducting magnets are installed in the KSTAR tokamak, especially for PF1UL to PF7UL of cable in conduit conductors are operating in AC mode and are generated AC losses such as a hysteresis loss, a coupling loss, an eddy current loss, etc. Hence, AC losses measurements were performed on PF1UL magnets with the largest and highest current with a high ramping rate among coils annually and an enthalpy method using for AC losses analysis. Experiments were performed on PF 1UL magnets for different ramping rates at 4 kA and 15 kA. The hysteresis loss at the same current is constant nearly and the coupling loss increases from 0.15 kA/s to 4 kA/s in proportion to the ramping rate. The coupling loss is proportional to the square of the magnetic field variation, and as the ramping rate approaches zero, the hysteresis loss is predicted to dominate. However, a sudden increase in loss occurred below 0.5 kA/s. An AC waveform of the current was observed. Therefore, in this paper, we would clarify the hysteresis loss of the KSTAR PF1UL magnets by numerically separating the loss caused by the AC waveform from the low ramp rate.