Low loss niobium flexure suspension systems

Niobium membrane flexure suspensions have been proved to be able to achieve high pendulum Q-factors, whereas niobium cantilever suspensions have been proved to give high internal Q-factors in sapphire test masses. Here we present the proposed sapphire test mass suspension systems based on the use of niobium flexures. This suspension system has the advantage of being robust while maintaining the high Q of the sapphire test mass. We show that it is also advantageous to use Nb flexures in future cryogenic detectors.