Nonlinear Observer of the Thermal Loads Applied on the Helium Bath of a Cryogenic Joule-Thompson Cycle Observer Design and Experimental Validation

In this paper, a nonlinear observer of the thermal loads applied to the helium bath of a cryogenic refrigerator is proposed. The thermal loads represents a time-varying thermal disturbance expected to take place in future tokamak refrigerators such as those used in the cooling systems for the International Thermonuclear Experimental Reactor (ITER) or the Japan Torus-60 Super Advanced (JT-60SA). The proposed observer can serve as monitoring tool for cryogenic operators and/or in observer-based advanced control strategies. The observer is based on a part of the nonlinear model of the refrigerator. The paper details the structure of the observer and validates its performance using experimental data.