A Re-Entrant MgB_2 Cavity for Dynamic Casimir Experiment

The use of radio frequencies (RF) superconducting re-entrant cavities has been suggested in the framework of some research to detect photon generation from the vacuum, due to the dynamical Casimir effect. A thin semiconducting slab, put inside the cavity, will be excited by a train of laser pulses of a frequency twice the resonant frequency of the cavity, so that a periodic modulation of the dielectric constant of the slab will be realized. In order to produce a RF cavity that can safely work at temperatures larger than 4 K, we have designed and constructed a MgB2 re-entrant cavity having a resonant frequency in the range of 2-3 GHz. The cavity is made by a cylindrical cup of about 40 mm of internal diameter and 40 mm of height and on its base is standing a cylindrical coaxial nose on which the semiconductor slab will be deposited. The details of the construction of the MgB2 cavity will be presented as well as the measurements of its quality factor, as a function of the temperature.