Conveners
SRF Thin Film Characterization: 1
- Lorena Vega (CERN)
SRF Thin Film Characterization: 2
- Eric Lechner (Jefferson Lab)
SRF Thin Film Characterization: 3
- Tsuyoshi Tajima (Los Alamos National Laboratory)
SRF Thin Film Characterization: 4
- Claire Antoine (CEA)
Measuring the surface resistance of samples is key for identifying and optimizing suitable materials and coated structures for SRF cavities with performances beyond the limits of niobium. The Helmholtz-Zentrum Berlin (HZB) routinely operates a Quadrupole Resonator (QPR) for the characterization of SRF samples. Over the past years, the setup has been continuously improved and now allows...
Nowadays, the most used superconducting cavities are generally made of bulk Niobium. The high quality of today’s processes uses an accelerating gradient very close to Niobium limit. New materials such as Nb3Sn, NbN and MgB2 that have higher critical temperature and magnetic field must be investigated to improve acceleration capabilities. As these materials could only be used as thin films, the...
A cost-effective facility for testing planar thin film samples under RF conditions has recently been commissioned at Daresbury Laboratory. This facility utilises a bulk Nb choked test cavity operating at 7.8 GHz, housed within a dry, liquid helium free cryostat. It is used to make low power surface resistance measurements of 10 cm diameter samples at temperatures down to 4 K and sample surface...
CERN has pioneered development of thin film superconducting radio-frequency cavities for particle accelerators. This technology has been applied in LEP II, LHC and more recently in HIE-ISOLDE. Many efforts are put in place at CERN in view of its potential implementation in the FCC machines. However, niobium thin film cavities historically feature a progressive degradation of performance by...
Many current accelerators use cavities that are manufactured as two half cells that are electron beam welded together, the weld is across the peak surface current of the cavity. This weld can lead to large increases in surface resistance and limit the performance of thin film coated cavities. Many problems with the coating process for thin film Superconducting Radio Frequency (SRF) cavities...
We analyzed omega (ω) phase transition in Nb thin film deposited by high power impulse magnetron sputtering (HiPIMS) using transmission electron microscopy (TEM) [1]. ~170 nm Nb thin film is deposited on Si (100) substrate and it showed a typical columnar structure with (110) texture on the surface. TEM analysis revealed that the Nb thin films contain ~1 vol.% of hexagonal structured omega...
The material of choice for current SRF accelerators is bulk Nb which is reaching the theoretical limits in terms of maximum accelerating gradient, Eacc. One method to increase Eacc is to use superconductor-insulator-superconductor, SIS, structures, where the thin films on the surface are smaller than the London penetration depth to screen the applied field, Bapp, such that the thicker...
The development of specialized materials is required to surpass the material limits of bulk Nb superconducting radio frequency (SRF) cavities. Indeed, SRF is a surface phenomenon in superconducting materials with an RF penetration depth of hundreds of nanometers. At these thicknesses, thin films can be tuned to achieve specific superconducting and RF properties. Layering thin films provide...
The maximum accelerating gradient of niobium radio frequency cavities are currently reaching their theoretical limits. It can be enhanced by increasing the cavity’s peak surface magnetic field at which the magnetic field penetrating into the superconductor in the form of vortices. To delay the penetrating of vortices into the bulk Nb, SIS structure which is superconductor (S) and insulator (I)...
We report evidence for counter current flow in superconductor-superconductor (SS) bilayers from depth-resolved measurements of their Meissner screening profiles using the low energy muon spin rotation (LE-$\mu$SR) technique. In these experiments, the implantation depth of the muons can be tuned/adjusted/controlled between ${\sim 10}$ nm and $\sim 150$ nm, below the surface, wherein their...
