The present invention provides a shaft-cylinder assembly for high-temperature operation comprising a pair of first and second dynamic sealing members having a helical coiled seal ring structure configured to be in contact with the shaft for providing dynamic sealing function in the cylinder; and a cylindrical cooling jacket configured to circumferentially surround the dynamic sealing members such that a cavity is defined between the dynamic sealing members inside the cooling jacket; wherein the cooling jacket comprises one or more inflow cooling channels and one or more outflow cooling channels configured to communicating with the cavity and circulating a cooling fluid through the cavity for moving heat away from the dynamic sealing members.