Study On Cooling Process Of Superconducing Magnet For ADS Injection

Accelerator driven sub-critical system (ADS) has a very broad applicationprospects in nuclear waste disposal and fuel efficiency improvement. This paper focuson the current lead optimization and cooling process of superconducting magnet forADS injection (ADS superconducting magnet) as well as quench process.Current leads of ADS superconducting magnet connect the magnet with thepower supply station at room temperature. AS heat leaks through the leads are one ofthe major thermal loads of vertical test system for ADS superconducting magnet,optimization of current lead plays an important role in reducing the whole leaks ofvertical test system. This paper gives the optimal geometry of the current leads andthe temperature distribution along the length by theoretical analysis. The effect ofRRR value on performance of lead in overloaded current is analyzed. Unsteadyprocess in the cases of current loading and overloaded is simulated by CFD softwareCFX15.0. The results show that adding a relative-big-mass copper block to the coldend of current lead can decrease the temperature fluctuation rang there significantly.Cooling process of ADS superconducting magnet from room temperature to4.2K is expected to take dozens of hours. In order to find a safe, efficient andeconomical solution of magnet cooling, a numerical simulation has been carried outbefore the cooling testing of ADS superconducting magnet. It is founded that coolingwith liquid helium has a better effect than gas helium in the final stage of coolingprocess according to the simulation result which shows that cooling magnet with gashelium become pretty difficult below7K. The relationship of liquid heliumconsumption with initial temperature of magnet and the velocity of injecting heliumas well as the temperature change of magnet are analyzed. Starting from the purposeof economy, timeliness and safety of magnet, this paper proposes a new coolingprocess. The result of cooling test for ADS magnet is obtained. The actualtime-consuming of whole cooling process is20hours, among which gas heliumcooling stage takes16.5hours and accumulation of liquid helium takes3hours.Difference of simulation result and test result of cooling process is analyzed.When ADS superconducting magnet is charged, the ac loss and steady heat leaksof system may lead to a magnet quench, resulting in a large number of liquid heliumgasification in a short time and a sudden increase of helium mass flow in the export oftest dewar. The helium compressor of refrigeration system will automatically shutdown when the inlet mass flow exceed its maximum suction capacity of40g/s, causing safety hazards and economic losses. A quench process is simulated beforecharging test of ADS magnet, the result of which indicate that a single quench ofmagnet will not affect the safety of the system as liquid helium in the coolingchannels is limited and the energy of quench conduct to the magnet surface is quiteslowly. The magnet re-cooled to4.2K after quench need10min. ADSsuperconducting magnet runs stable during charging test, and magnet quench did notcause significantly higher helium flow in the export of test dewar, cooling systemrunning smoothly.