High resolution diagnostic tools for superconducting radio frequency cavities

Area of Science:

• Materials Science
• Particle Accelerator Technology
• Applied Physics

Background:

• Superconducting radio-frequency (SRF) cavities are essential components in particle accelerators, requiring operation at cryogenic temperatures for high performance.
• Trapped magnetic flux on SRF cavity surfaces is a primary cause of residual radio-frequency (RF) losses, hindering accelerator efficiency.
• Accurate measurement of trapped flux distribution is vital for understanding its correlation with cavity properties and environmental factors.

Purpose of the Study:

• To design, develop, and commission novel diagnostic tools for high-resolution measurement of trapped magnetic flux on SRF cavity surfaces.
• To investigate the spatial distribution of trapped magnetic flux and its dependence on experimental conditions.

Main Methods:

• Development of a magnetic field scanning system utilizing cryogenic Hall probes and anisotropic magnetoresistance (AMR) sensors with high spatial resolution (∼13μm azimuthal, ∼1 cm contour).
• Implementation of a stationary, combined magnetic and temperature mapping system with AMR and carbon resistor sensors for a 3 GHz SRF cavity, offering resolutions of 5 mm (iris) and 11 mm (equator).

Main Results:

• Demonstrated non-uniform distribution of trapped magnetic flux on SRF cavity surfaces.
• Observed that flux distribution is dependent on the applied magnetic field strength during field-cooling below the critical temperature.

Conclusions:

• The developed diagnostic tools provide high-resolution mapping of trapped magnetic flux on SRF cavities.
• These findings contribute to a better understanding of RF loss mechanisms and inform strategies for optimizing SRF cavity performance.