Magnetic shielding for superconducting RF cavities

Abstract

Magnetic shielding is a key technology for superconducting radio frequency (RF) cavities. There are basically two approaches for shielding: (1) surround the cavity of interest with high permeability material and divert magnetic flux around it (passive shielding); and (2) create a magnetic field using coils that cancels the ambient magnetic field in the area of interest (active shielding). The choice of approach depends on the magnitude of the ambient magnetic field, residual magnetic field tolerance, shape of the magnetic shield, usage, cost, etc. However, passive shielding is more commonly used for superconducting RF cavities. The issue with passive shielding is that as the volume to be shielded increases, the size of the shielding material increases, thereby leading to cost increase. A recent trend is to place a magnetic shield in a cryogenic environment inside a cryostat, very close to the cavities, reducing the size and volume of the magnetic shield. In this case, the shielding effectiveness at cryogenic temperatures becomes important. We measured the permeabilities of various shielding materials at both room temperature and cryogenic temperature (4 K) and studied shielding degradation at that cryogenic temperature.

Design and analysis of a hybrid magnetic shielding system: application for the magnetic non-destructive testing of circuits

“…According to the magnetic field before and after shielding, the SF reaches up to 99.9%. It is better than cylindrical superconducting RF cavity shield, whose residual magnetic field is 100 nT [20]. When the electromagnetic environment is relatively stable in the evening, the magnetic field in the shielding system is smaller and more stable, which ensures the operation of the precision magnetic measuring instruments.…”

Multilayer magnetic shielding for testing a superconducting single-flux-quantum circuit chip in liquid helium dewar

“…of neutral antimatter. Masuzawa [14] measured the permeabilities of various shielding materials at a temperature of 4 K for magnetic shielding of superconducting radio frequency cavities. It can be concluded that the shielding materials for cryogenic systems are usually low-temperature high permeability materials and superconducting materials.…”

Measurements of sub-nT dynamic magnetic field shielding with soft iron and mu-metal for use in linear colliders

“…A magnetic shield is used to prevent magnetic flux trapping. Studies of potential magnetic shields for ILC SRF cavities are presented in [12][13][14].…”

“…It was observed in [13,38] that the shielding factor of a mu-metal shield degrades at very low (superconducting) temperatures. This is only a concern for accelerators that operate at superconducting temperatures, such as the ILC.…”