Power Dependence of the RF Surface Resistance of MgB2Superconductor

Magnesium diboride (MgB2) is a superconducting material that has a transition temperature (Tc) of ∼40 K, which is ∼30 K higher than niobium (Nb) that has been used for most superconducting RF cavities in the past decades. Last year, it was demonstrated that the RF surface resistance of MgB2can be lower than Nb at 4 K. One of the problems with other high-Tc materials such as YBCO was its rapid increase in RF surface resistance with higher surface magnetic fields. Recently, we have shown that MgB2shows little increase in the surface resistance up to ∼120 Oe, equivalent of an accelerating field of ∼3 MV/m. The highest field tested was limited by available power. This result is encouraging and has made us consider fabrication of a cavity coated with MgB2and test it. Also, there is a potential that this material has a higher critical magnetic field that enables the cavity to run at a higher gradient than Nb cavities in addition to the possibility of operation at higher temperatures.