Power Dependence of the RF Surface Resistance of MgB2Superconductor

Magnesium diboride (M
g
B
2
) is a superconducting material that has a transition temperature (T
c
) 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 M
g
B
2
can 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 M
g
B
2
shows 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 M
g
B
2
and 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.