A Re-Entrant ${\hbox {MgB}}_{2}$ 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.