Magnesium diboride (MgB 2 ) has a transition temperature (T c ) of 40 K, i.e., about 4 times as high as that of niobium (Nb). We have been evaluating MgB 2 as a candidate material for radio-frequency (RF) cavities for future particle accelerators. Studies in the last 3 years have shown that it could have about one order of magnitude less RF surface resistance (R s ) than Nb at 4 K. A power dependence test using a 6 GHz TE 011 mode cavity has shown little power dependence up to 12 mT (120 Oe), limited by available power, compared to other high-T c materials such as YBCO. A recent study showed, however, that the power dependence of R s is dependent on the coating method. A film made with on-axis pulsed laser deposition (PLD) has showed rapid increase in R s compared to the film deposited by reactive evaporation method. This paper shows these results as well as future plans.
The mapping of outer wall temperature during the vertical test of a superconducting radio-frequency (SRF) cavity has been one of the most useful tools to detect bad spots of the cavity. However, few systems except a rotating-arm type one have been developed so far for 9-cell cavities. Since it will be an essential tool to identify the failure of the cavities, we started to develop a fixedboard-type temperature mapping system that will enable us to map the temperature of 9-cell cavities in a much shorter time than rotating-arm type. This paper describes the design, status of the development and preliminary tests of the design.
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