Research On Operation Control Of High-Speed Cryo-Adsorption Pump Of Negative On Based Beam Source Neutral Beam Injection System

For future fusion development needs,CFETR(China Fusion Engineering Test Reactor)NNBI(Negative ion based Neutral Beam Injector)validation prototype used high-speed cryo-adsorption pump as the main vacuum acquisition device,it can realize the functional requirements of instantaneous large pumping speed.Cryogenic vacuum system is one of the important subsystems of NNBI,which provides the necessary low temperature and vacuum environment for beam generation and transmission.A good vacuum environment plays an important role in improving the neutralization efficiency of the beam and reducing the reionization loss.The system employs a built-in ultra-high-speed cryo-adsorption pump utilizing forced-flow cooling as the main pump.Compared with the cryo-condensate pump,the cryo-adsorption pump adopted by the NNBI verification prototype has high ultimate pressure,high pumping speed and high pumping capacity,and lower requirements on the fluctuation of cooling capacity while effectively pumping hydrogen.Therefore,the cryo-adsorption pump is selected as the main pumping pump of the cryogenic vacuum system of the NNBI verification prototype,it can meet the engineering requirements of NNBI verification prototype test operationThe operation process of instantaneous high pumping speed cryo-adsorption pump system mainly includes four main processes:cooling,steady state operation,activation regeneration and warm-up,compared with other ultra-high vacuum pumping systems,the operation is more complex.Therefore,precisely controlling the operation control of high-speed cryo-adsorption pump,especially the activation regeneration process,has become a key engineering technical problem that must be solved in the development of the NNBI verification prototype and the steady-state operation test.Aiming at the basic features of the main functions such as rapid cooling,stable operation,activation regeneration and warm-up required by the operation of high-speed cryo-adsorption pump,The low efficiency of fusion engineering operation experiment due to the long regeneration time of natural activation and uncontrolled temperature was studied and analyzed.A control method for the operation of high-speed cryo-adsorption pump was proposed.At present,there are no mature technical research achievements at home and abroad.Therefore,it is of important engineering application value to carry out the research on the precise control of the operation of high-speed cryo-adsorption pump for the CFETR NNBI verification prototype.The main research contents of this paper are as follows:The temperature is an important operating parameter of cryo-adsorption pump,The temperature of the cryogenic adsorption surface and the radiation shield baffle need to be monitored in real time at key locations.In order to control the regeneration of the cryo-adsorption pump,the ability to heat the cryogenic adsorption surface to a set temperature is required.Based on the main performance parameters and design indexes of cryogenic vacuum system,the basic principle of low measurement is studied,and the temperature sensor is analyzed and selected.A multi-channel temperature measurement control unit based on the STM32 was designed to meet the temperature measurement requirements of the cryo-adsorption pump of the CFETR NNBI verification prototype,which operates in a complex radiation and electromagnetic environment.The temperature measurement range is from 4 K to 325 K in the helium zone and from 70 K to 450 K in the nitrogen zone.It not only measures 8 points simultaneously and transmits the data remotely to the upper computer,but also allows the temperature to be set by the upper computer.In addition,it is possible to control the regeneration process of the cryo-adsorption pump by controlling the heating of the heating wire via the STM32.The practical engineering problems of lead heat transfer and heat sink in low temperature measurement,the influence of magnetic field on temperature measurement and Joule heat of thermometer are analyzed and the solutions are put forward.Secondly,the operation process,regeneration mechanism and regeneration process of the cryo-adsorption pump are studied in detail.Aiming at the basic characteristics of the main processes such as rapid cooling,stable operation,activation regeneration and warm-up,etc.required by the operation of the high-speed cryo-adsorption pump.The key technical problems of natural activation regeneration,such as long recovery time and uncontrollable temperature,were studied and analyzed,and an efficient and safe controllable technical method for activation regeneration heating process was proposed.An regeneration heating experimental control system,including an equipment layer,control layer,data acquisition and monitoring layer,was designed to control the regeneration heating process of the cryo-adsorption pump.The signals collected by temperature sensors are processed and transmitted through signal isolators to the host computer for display and storage.The target temperature is manually set on the host computer.Considering the operation characteristics and parameter requirements of NNBI validation prototype,An improved generalized predictive control(GPC)algorithm and a fuzzy proportional integral derivative(PID)control algorithm are used in the control layer to control the heating process.In the control algorithm analysis part,the fuzzy control principle and the design of the fuzzy controller of the cryo-adsorption pump are introduced in detail,as well as the basic principle of predictive control and the improved generalized predictive control algorithm for the operation characteristics and parameter requirements of the NNBI verification prototype.At the same time,the approximate characteristic function of the object model is identified by parameter identification.The simulation results of different control schemes are verified by comparison experiments.Finally,a comprehensive test platform for the prototype of the cryo-adsorption pump was designed and built,and the test cover,single-module cryogenic pump,vacuum measuring system,refrigeration system and auxiliary pumping system composed of the comprehensive test platform were introduced in detail.The designed low measuring system and activation regenerative heating control system were embedded into the comprehensive test platform for the prototype of the cryo-adsorption pump.The comprehensive experimental test platform experiment was carried out.The experimental results showed that the low measurement of the high-speed cryo-adsorption pump and the activation regeneration heating control system could operate safely and stably.The activation regeneration heating process was controllable and efficient,which laid a foundation for the construction of the cryogenic and activation regeneration operation control system of the prototype cryo-adsorption pump.It also provides a design basis for the vacuum system operation monitoring requirements of fusion engineering experimental reactor and a design reference for similar requirements.