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The authors have undertaken basic research and prototype developments on various four valve pulse tube refrigerators (FVPTR) since several years. Systematic studies have been carried out to characterize the basics of the arising loss mechanisms of this type of pulse tube refrigerator with its active type of phase shifting. Recently, a single-stage FVPTR in coaxial arrangement has been designed for maximum refrigeration power at cooling temperatures below 30 K limited by an available electrical input power of 6.2 kW. At present the single stage cooler provides a cooling capacity of 10 W or 20 W at working temperatures of 22 K or 27 K, respectively. Instead of lead spheres, lead coated screens have been applied in the coldest part of the regenerator in order to decrease the pressure drop. The improvement of the refrigerator overcomes the well known shortcoming of a refrigerator with a regenerator partially filled with lead spheres at working-temperatures above 50 K. Numerical simulations of the thermodynamical process yield to continuative lead screen parameter studies. The results raise hope for achievable minimum temperatures down to 15 K. We report on the improved performance of the FVPTR due to the use of lead-coated screens. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]