Review of low beta structures [superconducting linear accelerators]

A number of superconducting linear accelerators for heavy ions are operational in the world, and their resonators are characterized by an optimum velocity in the range v/c=0.008-0.2. The design issues for these kinds of cavities are discussed. The choice of the superconductor, the various construction techniques, the most proper surface treatments and the conditioning procedures are reviewed, and updated performances reported. Advantages and drawbacks of the three major construction techniques are discussed. The most recent kinds of low beta superconducting cavities, such as modified quarter wave resonators and radiofrequency quadrupoles, are presented.