Vacancy-Hydrogen Interaction in Niobium during Low-Temperature Baking

Area of Science:

• Materials Science
• Superconductivity
• Particle Accelerators

Background:

• Superconducting radio frequency (SRF) cavities are crucial for particle accelerators.
• Surface losses limit the accelerating gradient in SRF cavities.
• TESLA shape cavities are a common design for SRF applications.

Purpose of the Study:

• To investigate the impact of a modified low-temperature baking process on superconducting TESLA shape cavities.
• To understand the role of vacancy-hydrogen complexes in reducing surface losses.
• To enhance the performance of particle accelerators through improved cavity properties.

Main Methods:

• Utilized Doppler broadening Positron Annihilation Spectroscopy (DB-PAS).
• Employed Positron Annihilation Lifetime Spectroscopy (PALS).
• Applied instrumented nanoindentation.
• Investigated samples from European XFEL niobium sheets.
• Studied vacancy evolution and hydrogen interaction during in-situ and ex-situ annealing at various temperatures.

Main Results:

• Modified low-temperature baking significantly reduces surface losses.
• An increase in the accelerating gradient of superconducting TESLA shape cavities was observed.
• Dynamics of vacancy-hydrogen complexes suppress lossy nanohydrides at 2 K.
• Enhanced accelerator performance is attributed to these microstructural changes.

Conclusions:

• Low-temperature baking is an effective method for enhancing SRF cavity performance.
• Understanding vacancy-hydrogen complex dynamics is key to optimizing superconducting materials.
• The findings contribute to the development of more powerful and efficient particle accelerators.