Institute Science and Technology of Accelerating Systems

Reducing the RF losses in superconductors for CW SRF applications

Superconducting radio-frequency (SRF) systems are the enabling technology for many next-generation, high-gradient accelerator applications, from energy-recovery linacs like BERLinPro to accelerator-driven systems. One big advantage of SRF systems lies in its low power dissipation so that continuous wave (CW) operation at high gradient is possible.  This opens up many new possibilities for future accelerator applications that are difficult (or impossible) to realize with pulsed copper systems.  However, while SRF cavities dissipate little power they must be cooled by liquid helium and for many CW accelerators the complexity as well as the investment and operating costs of the cryoplant can prove to be prohibitive.

An important focus of SRF R&D therefore lies on gaining a better understanding of the RF losses in superconductors with the goal to reduce them by up to an order of magnitude over what is routinely achieved with present-day niobium. Many mechanisms, such as the oscillation of unpaired electrons in the RF field, random material defects and trapped magnetic flux, contribute to the power dissipation and an understanding of these is essential to optimize the CW operation of SRF cavities.  The goal of our Q improvement program is

• to learn what contributes to the residual losses in niobium cavities (i.e., those that are not caused by field emission and other high-field loss mechanisms) and to develop treatment techniques that avoid these losses.  HIER LINK ZU 01-1-1_Q_improvement_program_JV
•  to study new materials that outperform niobium and/or are able to operate at higher bath temperature.  HIER LINK ZU 01-5-QPR_program-RK