PKU/IHIP, Beijing, People's Republic of China
JLAB, Newport News, Virginia, USA
PKU/IHIP, Beijing, People's Republic of China
JLAB, Newport News, Virginia, USA
This paper reports the research results of effects of cathode shapes during buffered and conventional vertical electropolishing treatments for single cell superconducting radio frequency (SRF) niobium cavities. Several different cathodes shapes such as, for instance, bar, ball, ellipsoid, wheel, etc. were employed. Detailed electropolishing parameters at different locations inside a single cell SRF cavity were measured using a unique JLab home-made demountable cavity, including I-V characteristic, removal rate, surface roughness, polishing uniformity and so on. It was demonstrated that optimal polishing results could be achieved by changing the cathode shape for both BEP and EP. Implications on the electropolishing mechanism of Nb cavities for both BEP and EP based on the obtained experimental results are discussed.
JLAB, Newport News, Virginia, USA
PKU/IHIP, Beijing, People's Republic of China
Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
PKU/IHIP, Beijing, People's Republic of China
JLAB, Newport News, Virginia, USA
For a normal superconducting radio frequency (SRF) cavity, it is hard to obtain detailed information of an electropolishing process. So, a demountable cavity was firstly made by JLab to resolve this problem. This paper reports the measurements of I-V characteristics at three different locations inside the demountable cavity during buffered electropolishing (BEP) and electropolishing (EP) treatments. The polishing plateau appeared earlier on the surface areas close to iris and later on those near equator. To find the reason for this phenomenon, the electric field distribution in the cavity was considered and simulated by means of Poisson Superfish. Correlations were found between the measured I-V characteristics and the simulated results. This implies that electric field distribution inside a SRF cavity had an important effect on the polishing processes during vertical BEP and EP.
JLAB, Newport News, Virginia, USA
PKU/IHIP, Beijing, People's Republic of China
As reported previously at the Berlin workshop, applying the JLab standard ILC EP recipe on previously BCP etched fine-grain multi-cell cavities results in improvement both in gradient and Q0. We recently had the opportunity to experiment with two 1300 MHz 9-cell large-gain niobium cavities manufacture by JLab and Peking University. Both cavities were initially BCP etched and further processed by using JLab’s standard ILC EP recipe. Due to fabrication defects, these two cavities only reached a gradient in the range of 20-30 MV/m. Interestingly both cavities demonstrated significant Q0 improvement in the gradient range of 15-20 MV/m. At 2K, a Q0 value of 2·1010 is achieved at 20 MV/m. At a reduced temperature of 1.8K, a Q0 value of 3·1010 is achieved at 20 MV/m. These results suggest that a possible path for obtaining higher Q0 in the medium gradient range is to use the large-grain material for cavity fabrication and EP and low temperature bake for cavity processing.
PKU/IHIP, Beijing, People's Republic of China
JLAB, Newport News, Virginia, USA
A computer program which was used to simulate and analyze the thermal behaviors of SRF cavities has been developed at Jefferson Lab using C++ code. This code was also used to verify the quench initiation due to geometrical defects in high magnetic field region of SRF cavities. We built a CEBAF single cell cavity with 4 artificial defects near equator, and this cavity has been tested with T-mapping. The preheating behavior and quench initiation analysis of this cavity will be presented here using the computer program.
daijin@pku.edu.cn
PKU/IHIP, Beijing, People's Republic of China
JLAB, Newport News, Virginia, USA
KEK, Ibaraki, Japan
Three kinds of geometrical features analysis techniques were adopted in association with cavity gradient R&D at Jefferson Lab: (1) Feature shape analysis by Kyoto camera system; (2) 3D shape analysis using a HIROX KH-7700 High Resolution Digital-Video Microscopy System; (3) Replica technique plus surface profiler for profile measurement of geometrical features. Up to now, many features were found in two nine cell SRF cavities: PKU2 from Peking University in China and NR1 from Niowave-Roark in America. Both of them have been RF tested at 2K. The shape analysis of geometrical surface features and correlation with RF test results using a thermal analysis code will be presented here.
daijin@pku.edu.cn
PKU/IHIP, Beijing, People's Republic of China
Superconducting RF technology has been developed at Peking University for more than 20 years. In the recent years, the researches are mainly focused on producing high performance superconducting cavities and installing the DC-SRF photocathode injector as well as related 2K cryogenic facility and other auxiliary equipment. The cavities designed and fabricated by Peking University mainly include TESLA type 9-cell cavities, 1.3 GHz 5-cell cavity for high current electron beam acceleration and 450 MHz spoke cavity for low energy proton acceleration. Vertical tests of the cavities indicate that the cavities show good performances and can be used for superconducting accelerators. The gradient of a 9-cell TESLA type cavity with end groups (PKU3) reaches 28.6 MV/m. To promote the industrialization process in China, a new company, Ningxia Orient Superconductor Technology Co., Ltd., was founded jointly by Ningxia OTIC and Peking University in 2011. The goal of this company is to produce various types of superconducting cavities and pure niobium materials with high quality.
PKU/IHIP, Beijing, People's Republic of China
DC-SRF photocathode injector developed by Peking University is a good candidate for obtaining high average current, low emittance, short electron beam pulse. Much progress has been made on the 3.5-cell cavity DC-SRF injector since SRF2009. The assembling of the cryomodule was completed with the 3.5-cell SRF cavity which has an accelerating gradient of 23.5MV/m in the vertical test. The preliminary RF experiment has been carried out soon after the installation and commissioning of 2K cryogenic system was finished. The accelerating gradient of the cavity is 11.5MV/m in a horizontal cold test and the Qext is 6×106 . The limitation of the gradient is mainly from our present low RF power source. Higher gradient is expected with a new 20kW solid state RF power source which will be delivered to Peking University soon.