A liquid helium-free cryostat for RF testing of superconducting cavities has been designed and constructed. G-M cryocoolers are used to provide cooling capacity, with heat leakage less than 0.02 W at 4 K. The vertical test of the Nb3Sn cavity and the horizontal test of the Nb cavity were carried out with the cryostat using different connection structures between the 4 K stage of the cryocooler...
At Daresbury Laboratory, fast RF characterisation of planar thin film coated samples is being performed on a dedicated facility. It is a LHe-free facility using a 7.8 GHz Choke Cavity to test planar samples 90-130 mm in diameter and 2-10 mm thickness. A simple sample mounting procedure, and straightforward measurements of surface resistance using an RF-DC compensation method, allows this...
Copper cavities can be deposited with a thin film of superconducting material in order to test the RF performance of the thin film. Traditional thin film copper cavities are produced from 2 half cells, which are then welded across the equator, however these cavities can suffer from poor coating quality and field enhancement on the weld.
An alternative approach instead involves producing...
At Daresbury Laboratory, two new cryogenic facilities have been designed, built and tested for RF testing of 1.3 GHz thin film coated cavities. The first facility is a high power vertical test stand that has been designed to test both single-cell and multi-cell cavities in LHe at 2 and 4.2 K. The advantage of this facility is that it will be operating in the SuRF lab facility that is already...
Superconducting radiofrequency cavities made of bulk Nb are reaching their theoretical limits in the maximum accelerating gradient, Eacc, where Eacc is limited by the maximum magnetic field, B, that can be applied on the surface of the accelerating cavity wall. To increase Eacc, the maximum B field, Bmax, which can be applied to the surface, must also be increased. The A15 materials or...
Coating Nb with thin layers of one or more superconductors with longer penetration depths, $\lambda$, has been proposed to achieve accelerating gradients, $E_{\mathrm{acc}}$, beyond Nb's fundamental limit. Such heterostructures can sustain the Meissner state above each layer's superheating field, $B_{\mathrm{sh}}$, due to the strong suppression of the screening currents in the surface layers...
"Positron annihilation spectroscopy (PAS) is a precise probe of point defects in nanomaterials. It enables to sense defect densities in the range of 1015-1019cm-3. Positrons localize in the neutral and negatively charged open volume defects, i.e. vacancies and their agglomerations, extended defects or pores. The time to annihilation of the positron with an electron depends on local electron...
A program of quantitative measurements of the expulsion of magnetic flux from flat macroscopic samples has been used to categorise expulsion efficiency, and to assess the practical expulsion effects of closed-topological cooling on thin film structures. Specifically, the closed-topology cooling has permitted systematic and repeatable measurements of the magnetic response over the...
Stable operation of a cavity generally requires Joule-heating, generated in its walls, to be conducted to an outer helium bath. Therefore, it is of interest to experimentally evaluate how present and future cavity treatments affect thermal characteristics. We present an instrument for measuring the thermal performance of SRF cavity materials at cryogenic temperatures. To get an idea of the...
