Two stage pulse tube coolers, could provide cooling capacity at dual temperature zones, exhibiting significant application value in fields such as space exploration, superconducting magnets, and quantum computing. To meet the requirements of nonlinear variable-load requirements in dual-temperature-zone, this paper proposes hybrid phase shifters: the first stage passive second stage active hybrid phase shifter and the first stage active second stage passive hybrid phase shifter.
Phase shifting mechnism analyses are firstly carried out.The motion state of active displacer piston could be actively controlled by the driving force, and the phase difference between the pressure wave and volume flow at the hot end of the pulse tube is adjusted accordingly, thereby changing the impedance of this stage and consequently affecting the interstage cooling capacity.
Numerical models are then constructed based on Sage software. For the first stage passive second stage active hybrid phase shifter, the cooling capacity can be adjusted from 0 to 17.5 W at 77 K and from 0 to 0.95 W at 20 K. With the decrease of the first stage cooling capacity, the maximum second stage cooling capacity is first increased and then decreased. The maximum first stage cooling capacity is reduced and the maximum second stage cooling capacity is increased by increasing the moving mass and mechanical damping.For the first stage active-second stage passive hybrid phase shifter, as the second stage cooling capacity increases, the maximum first stage cooling capacity first rises and then falls.A maximum value of 1.26 W at 20 K is obtained. Increasing the moving mass or mechanical damping of the second stage displacer would improve the maximum first stage cooling capacity while reduce the maximum second stage cooling capacity.
Finally, the maximum cooling capacity regulation ranges with hybrid phase shifters in various temperature zones are compared. For the first stage active second stage passive hybrid phase shifter, the maximum first stage cooling capacity first increases and then decreases with the rise of the maximum second stage cooling capacity .For the first stage passive second stage active hybrid phase shifter, as the first stage working temperature increases, the maximum achievable second stage cooling capacity first increases and then decreases with the reduction of the first stage cooling capacity.
Hybrid phase shifter could simplify the system structure and regular interstage cooling performance, providing a feasible technical solution for high-efficiency variable-load two stage pulse tube cooler.