Development of Superconducting RF Technology

The development of superconducting RF cavity technology started in the 1960s, aiming for continuous wave operation of high gradient linacs with excellent electric power efficiency. After continuous efforts for more than four decades, the initial achievable field gradient of only 2MV/m was gradually improved and approached the theoretical upper limit of 50MV/m on Nb cavities. At each stage of this development, many applications have been extended in various fields. This article will review those advances and applications of the superconducting RF cavities.