IIT, Chicago, Illinois
JLAB, Newport News, Virginia
ANL, Argonne
We have shown previously that magnetic niobium oxides can influence the superconducting density of states at the surface of cavity-grade niobium coupons. We will present recent results obtained by Point Contact Tunneling spectroscopy (PCT) on coupons removed from hot and cold spots in a niobium cavity, as well as a comparative study of magnetic oxides on mild baked/unbaked electropolished coupons. We will also describe recent results obtained from coated cavities, ALD films properties and new materials using Atomic Layer Deposition (ALD).
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
JLAB, Newport News, Virginia
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
BNL, Upton, Long Island, New York
DESY, Hamburg
FZD, Dresden
MBI, Berlin
In this paper we describe the R&D roadmap at HZB for the development of a high-brightness, high average current SRF electron gun for an energy-recovery linac based synchrotron radiation source.
BARC, Mumbai
JLAB, Newport News, Virginia
BARC-EBC, Mumbai
In recent years, large-grain/single-crystal niobium has become a viable alternative to the standard fine grain (ASTM grain size>6), high purity (RRR ) niobium for the fabrication of high-performance SRF cavities for particle accelerators In this contribution we present the results of a systematic study of the superconducting properties of samples obtained from four Niobium ingots (from CBMM, Brazil) of different purity. Measurements of bulk magnetization, surface pinning, critical temperature and thermal conductivity have been carried out on the samples subjected to different surface treatments such as buffered chemical polishing (BCP), 600C heat treatment, and low temperature baking (LTB). A correlation has been established between the LTB and the ratio of Hc3/Hc2. In addition, the phonon peak in the thermal conductivity data is suppressed by the presence of trapped magnetic vortices in the samples
FZD, Dresden
JLAB, Newport News, Virginia
An SRF photoinjector has been successfully tested in FZD under the collaboration of BESSY, DESY, FZD, and MBI. In order to improve the gun cavity quality and thus reach a higher gradient, a new 3+1/2 superconducting cavity is being fabricated in cooperation with JLab. The modified cavity is made of large grain niobium, composed of one filter choke, one special designed half-cell (gun-cell) and three TESLA cavities. In this paper, the main updates of the new cavity design will be explained in detail. The deformation of the filter choke and the gun-cell, which is caused by pressure fluctuation in the He-line and also by the effect of the Lorentz force, will be minimized by stiffening between the filter choke and the gun-cell. Meanwhile, the cathode hole in the choke and gun-cell is enlarged for better rinsing. To simplify assembly, the NbTi pick-up will be welded directly on the wall of filter choke.
JLAB, Newport News, Virginia
DESY, Hamburg
We have in the past reported about our efforts to develop a flangeable coaxial coupler for both HOM and fundamental coupling for 9-cell ILC-type cavities. The design of the coupler was done in a way, that the rf magnetic fields at the flange connection were minimized and only a field of <5 mT would be present for a magnetic field of 160 mT ( Eacc ~ 35 MV/m) in the cavity. Even though we achieved reasonably high Q-values at low field, the cavity/coupler combination was limited to only ~ 7 MV/m in the cavity, where a thermally initiated degradation occurred. We believed that this limitation was caused by poor cooling of the shorting plate in the coaxial coupler; therefore, we have improved the cooling conditions by drilling radial cooling channels into the shorting plate. This paper reports about our experiences with the modified conditions.
JLAB, Newport News, Virginia
DESY, Hamburg
Performance of 3-Cell Seamless Niobium Cavities P. Kneisel, G.Ciovati, Jefferson Lab and X.Singer, W.Singer, I. Jelezov, DESY In the last several months we have surface treated and cryogenically tested three TESLA-type 3-cell cavities, which had been manufactured at DESY as seamless assemblies by hydroforming. The cavities were completed at JLab with beam tube/flange assemblies. All three cavities performed very well after they had been post-purified with titanium at 1250C for 3 hrs. The cavities, two of which consisted of an end cell and 2 center cells and one was a center cell assembly, achieved gradients of Eacc = 32 MV/m, 34 MV/m and 35 MV/m without quenches. The performance was limited by the appearance of the “Q-drop” in the absence of field emission. This contribution reports about the various measurements undertaken with these cavities.