In ordinary conductors, electrons can lose energy by two mechanisms. First, by electron scattering on atoms of the lattice bulk, thus transferring energy to the bulk and increasing the bulk's temperature. This is the main contribution to the conductor resistance. But there is also the second mechanism; by radiating electromagnetic radiation due to electron acceleration. In a closed conducting circle electrons move circularly, and therefore have some acceleration, and therefore radiate. This is a relatively small contribution to the total rate of energy loss, but is not zero. Now superconductors! In superconductors, the bulk has an energy gap, so electrons (or more precisely, Cooper pairs) cannot transfer an arbitrarily small energy to the bulk. This prevents the first mechanism of loosing electron energy. But I don't see that anything prevents the second mechanism. In superconductors, electrons should still lose energy by producing electromagnetic radiation. As far as I know, there is no energy gap for the superconducting electrons themselves (the gap exists only for the bulk). So why don't they radiate? Or perhaps they do?