Magnetometric mapping of superconducting RF cavities

Schmitz, Benedikt; Köszegi, Julia-Marie; Alomari, Khaled; Kugeler, Oliver; Knobloch, Jens

doi:10.1063/1.5030509

Cited by 12 publications

(5 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The rest of this review focuses on rf losses of Abrikosov vortices with normal cores [18]. Such vortices trapped by a random pinning potential of materials defects can bundle together, forming localized hotspots which have been revealed by temperature mapping of Nb cavities [30,79,80] and thin film structures [81,82], as well as by magnetic mapping [257][258][259]. Unlike hotspots caused by lossy materials defects, vortex hotspots can be moved or fragmented by temperature gradients produced by external heaters [119] or scanning laser [80,120,260,261] or electron [262,263] beams.…”

Section: Trapped Vorticesmentioning

confidence: 99%

Tuning microwave losses in superconducting resonators

Gurevich

2023

Supercond. Sci. Technol.

View full text Add to dashboard Cite

Performance of superconducting resonators, particularly cavities for particle accelerators and micro cavities and thin film resonators for quantum computations and photon detectors has been improved substantially by recent materials treatments and technological advances. As a result, the niobium cavities have reached the quality factors $Q\sim 10^{11}$ at 1-2 GHz and 1.5 K and the breakdown radio-frequency (rf) fields $H$close to the dc superheating field of the Meissner state. These advances raise the question whether the state-of-the-art cavities are close to the fundamental limits, what these limits actually are, and to what extent the $Q$ and $H$ limits can be pushed by the materials nano structuring and impurity management. These issues are also relevant to many applications using high-Q thin film resonators, including single-photon detectors and quantum circuits. This topical review outlines basic physical mechanisms of the rf nonlinear surface impedance controlled by quasiparticles, dielectric losses and trapped vortices, as well as the dynamic field limit of the Meissner state. Sections cover ways of engineering an optimum quasiparticle density of states and superfluid density to reduce rf losses and kinetic inductance by pairbreaking mechanisms related to magnetic impurities, rf currents, and proximity-coupled metallic layers at the surface. A section focuses on mechanisms of residual surface resistance which dominates rf losses at ultra low temperatures. Microwave losses of trapped vortices and their reduction by optimizing the concentration of impurities and pinning potential are also discussed.

show abstract

Section: Trapped Vorticesmentioning

confidence: 99%

Tuning microwave losses in superconducting resonators

Gurevich

2023

Supercond. Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…The HZB developed a temperature-and magnetic-fieldmapping system which can be applied to single-cells during the rf tests with a three-dimensional control over the ambient magnetic field using three sets of Helmholtz-coils [30]. Several measurements of 1DE16 with this set up installed were done.…”

Section: Measurements At Hzbmentioning

confidence: 99%

Nitrogen infusion R&D at DESY a case study on cavity cut-outs

Wenskat

Bate

Pandey

et al. 2020

Supercond. Sci. Technol.

View full text Add to dashboard Cite

A first series of nitrogen infusion runs of 1.3 GHz single-cell cavities at DESY resulted in an unexpected and severe deterioration observed during the vertical cold test. To investigate the origin of the deterioration, one of the cavities underwent extensive radio-frequency measurements and a temperature- and magnetic field-mapping was performed in collaboration with the Helmholtz-Zentrum Berlin. After combining all results, regions of interests were identified and cut-out of the cavity. Subsequent surface analysis techniques (EBSD, PALS, PIXE, SEM/EDX, SIMS, XPS) were applied in order to identify the microscopic origin of the deterioration and especially the differences between hot and cold spots as well as quench spots. An excess of niobium carbides, reducing the thermal conductivity, was identified as the probable cause for the deterioration, and the size- and density-distributions were observed to be crucial for the resulting performance reduction. The origin for the local differences in the niobium carbide formation between hot and cold spots is an effect of preexisting variations of the crystal structure.

show abstract

“…In particular, it was found that the size of trapped flux is affected by several different parameters, such as the cooldown conditions or material properties like RRR (residual resistivity ratio). This laid the basis for further, systematic investigations [1][2][3][4][5][6][7][8][9][10][11]. These methods have in common that the magnetic flux is observed indirectly-either by measuring its impact on the cavity performance or by measuring the impact of the incomplete Meissner transition on the ambient magnetic field or by small angle neutron scattering.…”

Section: Introductionmentioning

confidence: 99%

Study of Possible Frequency Dependence of Small AC Fields on Magnetic Flux Trapping in Niobium by Polarized Neutron Imaging

2021

View full text Add to dashboard Cite

Reducing the size of ambient magnetic flux trapping during cooldown in superconducting radio-frequency niobium cavities is essential to reaching the lowest power dissipation as required for continuous wave application. Here, it is suggested that applying an alternating magnetic field superimposed to the external DC field can potentially reduce the size of trapped flux by supporting flux line movement. This hypothesis is tested for the first time systematically on a buffered chemically polished (BCP) niobium sample before and after high temperature annealing, a procedure which is known to reduce flux pinning. External low-frequency (Hz-range) magnetic fields were applied to the samples during their superconducting transition and the effect of varying their amplitude, frequency and offset was investigated. A few results can be highlighted: The influence of the frequency and magnitude of the AC fields on the flux trapping in the untreated Nb sample cannot be neglected. The trapped flux seems to be homogeneously distributed, unlike the flux trapping in, e.g., lead (Pb), which is a type I superconductor. After annealing, the Nb sample shows practically no dependency of flux trapping on external AC fields. The trapped magnetic flux was measured by polarized neutron imaging, and calculations of trapped fields show good agreement with experimental results.

show abstract

Magnetometric mapping of superconducting RF cavities

Cited by 12 publications

References 14 publications

Tuning microwave losses in superconducting resonators

Tuning microwave losses in superconducting resonators

Nitrogen infusion R&D at DESY a case study on cavity cut-outs

Study of Possible Frequency Dependence of Small AC Fields on Magnetic Flux Trapping in Niobium by Polarized Neutron Imaging

Contact Info

Product

Resources

About