A cooling system (40) for providing cryogenic cooling fluid to an apparatus (1) comprises a re-circulation device (2), a passive cold storage device (11) having a porous matrix of material which directly contacts the cryogenic cooling fluid as the cryogenic cooling fluid passes through the passive cold storage device, a first portion of a fluid communication feed line (20a) fluidly connecting the re-circulation device (2) to the passive cold storage device (11), a second portion of a fluid communication feed line (20b) fluidly connecting the passive cold storage device (11) to the apparatus (1) for communicating cryogenic cooling fluid to the apparatus, and a fluid communication return line (20c) fluidly connecting the apparatus (1) to the re-circulation device (2). The passive cold storage device (11) may comprise a regenerative heat exchanger including a porous matrix of metal wire mesh, metal spheres or ceramic spheres.