| The Neutral Beam Injector?NBI?is a complex system that generates a beam of high-energy neutral particles to heat the fusion plasma and drive the plasma current.The vacuum system is an indispensable component of NBI and it's performance directly affects the generation,neutralization and beam transmission efficiency of the ion beam.With the deepening of fusion research,the design of NBI vacuum system using cryogenic pump has become an inevitable choice.Cryoadsorption has the typical advantages of high vacuum limit?good stability and helium extraction compared with cryocondensation which is current mainstream of NBI design,.So cryoadsorption pumping is more suitable for future fusion reactor NBI,so it is of great significance to carry out cryoadsorption mechanism and performance test experimental research for fusion development needs.The main work of this paper is as follows:Firstly,the cryogenic pumping technology and its application status in neutral beam system were investigated.The pumping mechanism of cryoadsorption and the adsorption isotherm describing cryoadsorption and the theoretical model of cryoadsorption were analyzed.Secondly,several adsorbent materials used in cryogenic vacuum environment were compared,and six coconut shell activated carbon adsorbents were selected for experimental research on nitrogen cryoadsorption capacity method.Based on the adsorption theory model,the structural performance parameters of the adsorbent were calculated and analyzed.The results show that the specific surface area of AC1 and AC2is different from the specific pore volume but the proportion of micropores is different.Therefore,the two activated carbons are selected as adsorbents for subsequent performance experiments.Then,a set of cryoadsorption performance test platform was designed and built to explore the influence of different factors on the cryoadsorption performance of the adsorbent.The platform is based on the test room and is equipped with five systems:cryogenic,vacuum,gas supply,measurement control and activation regeneration.It realizes functions such as cooling,temperature control,vacuuming,intake and measurement data.According to the cold array structure of the platform,the numerical simulation method is used to analyze the cooling characteristics,and the steady temperature distribution and cooling time of the cooling are simulated.The results show that the cryosystem meets the requirements of the experiment,and the cooling time is better than the measured results.Finally,based on the built test platform,the effects of different gas loads,adsorption surface temperatures and different adsorbates on the pumping performance of the two adsorbents were investigated.The results show that in the range of 10-4-10-22 Pa airborne range and 4 K-10 K temperature range,the pumping speed of hydrogen by two adsorbents decreases with the increase of air load and temperature,The pumping performance of microporous adsorbent was better than that of medium pore type adsorbent.The pumping speed was better than the EAST-NBI cryogenic condensate pumping speed.The cryoadsorption pumping behavior of the hydrogen/helium mixed gas was studied by using the residual gas analyzer.It was found that the microporous adsorbent was selective for the adsorption of hydrogen/hulium mixed gas at different temperatures. |
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