The properties of vacuum components working at cryogenic temperature represent a crucial aspect to assure accelerator's best performances. Recently, pulsed laser processing of Cu samples (LASE-Cu) has been demonstrated to produce rough surfaces, whose structuring at the nanoscale ensures an impressive reduction of the secondary electron yield and, then, of electron cloud phenomena. This feature has such undoubted appealing that LASE samples have been proposed to be integrated in the cryogenic beam screen of FCC-hh. However, the effective application of LASE surfaces requires a rigorous evaluation of their vacuum behavior at cryogenic temperatures.
To this aim, the behavior of a LASE-Cu substrate has been studied by thermal programmed desorption and compared to flat Cu. Ar, CO, CH$_4$ and H$_2$ have been cryosorbed at 15 K on both surfaces and their desorption has been followed between 20 and 70 K. Our results highlight that the sponge-like structural features determines for the LASE sample non-negligible effects due to the gas-substrate interaction. This results in a much vaster and higher desorption temperature range with respect to what is observed from the flat substrates.
On these bases, although the electron cloud mitigation efficiency has been settled, before definitely including porous surfaces in any cryogenic machine design, all the consequences of having a rough rather than a flat wall should be carefully evaluated. Photo and electron induced desorption yield should also be carefully studied to validate any new material to be used in FCC-hh.