Direct current magnetic Hall probe technique for measurement of field penetration in thin film superconductors for superconducting radio frequency resonators

The superheating field H s h of the Meissner state is thought to determine the theoretical field-limit of superconducting accelerator cavities. We investigate H s h of semi-infinite superconductors and layered structures in the diffusive limit using the well-established quasiclassical Green’s function formalism of the BCS theory. The coupled Maxwell–Usadel equations are self-consistently solved to obtain the spatial distributions of the magnetic field, screening current density, penetration depth, pair potential, and H s h . For a semi-infinite superconductor in the diffusive limit, we obtain H s h = 0.795 H c 0 at the temperature T → 0 . Here, H c 0 is the thermodynamic critical-field at the zero temperature. By laminating a superconducting film (S) with the thickness d on a semi-infinite superconductor (Σ), we can engineer H s h ( d ) of the layered structure. When d is the optimum thickness d m , H s h can be larger than that of the simple semi-infinite superconductors made from the S and Σ materials: H sh ( d m ) > max { H sh ( S ) , H sh ( Σ ) } . The present study addresses the calculation of H s h of the dirty heterostructure using the microscopic theory from beginning to end for the first time, which contributes to the microscopic understanding of the surface engineering for pushing up the accelerating gradient of superconducting cavities for particle accelerators.

“…Progress in experiments is summarized in [22] (see also progress in the last several years, e.g. [23][24][25][26][27][28][29][30][31][32][33][34]).…”

Section: Introductionmentioning

confidence: 99%

Superheating fields of semi-infinite superconductors and layered superconductors in the diffusive limit: structural optimization based on the microscopic theory

Kubo

2021

“…A future aim is to compare results produced by the DC magnetic field penetration facility to other local magnetometer techniques such as the field penetration measurement at Old Dominion University [22] and the 3rd harmonic system [1]. Finally, the field penetration system should be compared to RF characterisation techniques such as a quadrupole resonator or the RF choke cavity at STFC Daresbury Laboratory [5] to determine if there is any correlation between devices or if the field is DC or RF.…”

Section: Discussionmentioning

confidence: 99%

“…Antoine et al have developed an AC magnetic susceptibility and third harmonic measurement system [1,10,[13][14][15] to study flux dynamics. A joint team from Old Dominion University and Thomas Jefferson National Laboratory have built a DC penetration measurement set-up [22]. Both these methods produce magnetic field by using a coil placed on a sample with an axis perpendicular to the sample surface.…”

Section: Introductionmentioning

confidence: 99%

A facility for the characterisation of planar multilayer structures with preliminary niobium results

Turner

Malyshev

Junginger

et al. 2022

The maximum accelerating gradient of superconducting radio frequency (SRF) cavities are currently reaching their theoretical limits, due to the magnetic field entering the superconductor in the form of vortices. To overcome these limits, thin film coated superconducting materials are required, however these need to be tested to optimise their properties. A system has been designed, built, and commissioned at Daresbury Laboratory that applies a local DC magnetic field parallel to the surface, from one side of a sample, similar to that in cavity operation. A magnetic flux density (up to 600 mT) is generated parallel to the sample surface in the 2 mm gap of a C-shaped ferromagnetic yoke. Two Hall probe sensors are used to measure both the applied and penetrated magnetic field. The system operates in a cryogen free environment, with a minimum temperature of approximately 2.6 K. A Pb foil has been used to characterise the system, and determine how the sample size affects the results. Nb thin film samples have been tested for varying thickness to determine how the depth effects the field of full flux penetration, Bfp. The design, operation, methods of analysis and first results of this facility will be reported in this paper.

“…Confinement of the rf power in a thin S layer inhibits expansion of multiple vortex loops in the bulk and blocks dendritic thermomagnetic avalanches that are particularly pronounced in Nb 3 Sn, NbN or pnictides which have low σ s and the thermal conductivity k [224,245]. Yet a thin Nb 3 Sn layer with d ∼ 100 nm only slightly increases the thermal impedance of the cavity wall, is the lack of experimental techniques capable of applying a strong parallel rf field H a ∼ H c to a thin film or a multilayer without dissipative penetration of vortices.…”

Section: Insulating Layersmentioning

confidence: 99%

“…The challenge with the measurements of R s (B a ) at high fields on materials with H c > H Nb c is the lack of experimental techniques capable of applying a strong parallel rf field H a ∼ H c to a thin film or a multilayer without dissipative penetration of vortices. Recently, Hall probe setups to measure a dc penetration field which quantifies the field onset of strong vortex dissipation in high-H c film coatings were developed [239,244]. The local nonlinear response of the Nb surface has been probed with a near-field magnetic microwave microscope [245].…”

Section: Surface Nanostructuringmentioning

confidence: 99%

Tuning microwave losses in superconducting resonators

Gurevich

2023

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.