JLAB, Newport News, Virginia
A major portion of the ILC R&D effort is focused on increasing the sustainable gradients in the baseline TESLA-shape SC cavities. This is a world-wide effort with major contributions from DESY (in parallel with their XFEL program), JLAB, FNAL and KEK. During the past year, the work in the US and Japan has ramped up considerably, and PAC09 is an opportune time to review the contributions from the groups in these regions, as well as at DESY.
KEK, Ibaraki
JLAB, Newport News, Virginia
The Electro-polishing process is the best candidate of final surface treatment for the production of ILC cavities. Nevertheless, the broad distribution of the gradient caused by field emitters in cavities is sitll a serious problem for the EP process. Ethanole- and degreaser-rinse processes after the EP process were found to be effective to decrease the field emmitter in recent studies, however, these are not perfect yet. We tried to test the sponge cleaning as the post EP process to remove the field emitter inside the cavcity. This article describe the results of series tests with a proto-type sponge-cleaning tool for single-cell cavity at KEK.
JLAB, Newport News, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
The great majority of experience in niobium SRF cavity processing at Jefferson Lab is with BCP etching. This has been used on CEBAF cavities and others totaling over 500 in number. With improved process quality control, field emission is now largely controlled and other factors limit performance. All of the prototype cavities developed for the 12 GeV upgrade, although meeting minimum requirements, have demonstrated a Q-drop in the 17 23 MV/m range that is not remedied by 120 C bake. Most of these cavities received >250 micron removal by BCP etch. Three of these cavities are being electropolished using the protocol under development within ILC R&D activities. The first such cavity was transformed from Q = 3 ·1010 at 17 MV/m to quench from 1010 at 35 MV/m. The details of this and two subsequent electropolished JLab 7-cell cavities will be reported.
JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Much remains to be learned regarding the details of SRF performance effects with material variation, including niobium treated in different ways, and different bulk/thin film materials that are fabricated under different conditions. A facility that can measure small samples’ RF properties in a range of 0~180mT magnetic field and 2~20k temperature is necessary in order to answer this question. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. The SIC system uses a sapphire-loaded cylindrical Nb cavity at 7.5GHz with 50mm diameter flat sample placed on a non-contacting end plate and a calorimetric technique to directly measure the rf dissipation in the sample in response to known rf fields over ~1 cm2. We report on the commissioning of this system and its first uses for characterizing materials. Preliminary tests with Nb thin film sample sputtered on Cu substrate, and bulk Nb sample have been done at low field. The presently available hardware is expected to enable tests up to 20 mT peak magnetic field on the sample CW. Paths to higher field tests have been identified.