Cavity Processing

Buffer Chemical Polishing

Through a Memorandum of Understanding, Fermilab and Argonne National Laboratory will collaborate on superconducting cavity processing for the International Linear Collider. A Buffered Chemical Polishing (BCP) system, designed for processing 3.9 GHz cavities, was assembled at Argonne National Laboratory. This facility will remain as the sole BCP processing location for the Fermilab 3.9 GHz cavity program. Reconfiguration of the BCP system for the 1.3 GHz processing is now underway.

Argonne installed and commissioned a large ultra pure water (UPW) plant and distribution as part of the overall Joint Superconducting Surface Processing Facility (SCSPF) infrastructure. An unaffiliated analytical laboratory verified the UPW quality met required specifications. The UPW infrastructure services the entire SCSPF including both the Argonne and Fermilab chemistry and cleanrooms. Argonne also plans to use UPW for high pressure rinsing electropolished resonators.

Cavity handling and manipulation occurs through the use of rather complicated hardware, all of which must be designed, developed, and fabricated or purchased. To quicken the pace of this hardware development, Fermilab will consult with other laboratories (DESY, JLab, Cornell) who have experience handling ILC style cavities.

A formal safety review of the Fermilab BCP system will be conducted following the water commissioning phase of the reconfigured BCP system. Prior to the safety review, Fermilab must develop significant procedural and safety documentation. The safety review will likely occur in the beginning of calendar year 2007.

Following a successful safety review, the ANL Physics Division will grant the approval to perform chemical procedures with the Fermilab BCP system. Fermilab plans to chemically polish both the inside and outside surfaces of 1.3 GHz ILC style cavities soon after approval is granted.

As part of the formal operation of the SCSPF, anyone working on chemical processes must receive formal training in chemical hygiene, emergency and processing procedures, and SCSPF operations. This training will begin in the last quarter of FY06 and continue into FY07.


A technique called electropolishing is currently emerging as a method to produce superclean superconducting radiofrequency cavities. Using the same principles of electrolysis, a cavity gets immersed in an acid bath. A current then runs through it to create the super smooth surfaces that are necessary for achieving high acceleration gradients. Scientists around the world are studying this technology for possible mass-production use on the ILC. Fermilab has several new activities that focus on electropolishing.

In close collaboration with Argonne National Laboratory, Jefferson Laboratory and Los Alamos National Laboratory, Fermilab explored the electropolishing input variables and defined the proper set of working parameters to allow consistent control of the process. This task is still ongoing, mainly at JLab, where it is possible to perform electropolishing on 9-cell cavities. Wider global collaborative efforts are focused on developing a specification document aimed at the standardization of the electropolishing parameters.

A joint Argonne-Fermilab panel generated a scenario to describe the path toward electropolishing industrialization by 2009, which led to the funding of an R&D electropolishing unit to be installed at the joint Argonne-Fermilab facility. The Fermilab group is also working on the fluid-dynamic optimization of the cathode, testing a number of components that might simplify the setup.

In order to gain electropolishing experience, Fermilab created a single cell setup. Due to the present limited acid handling capabilities, initially this unit will only be able to electropolish 3.9 GHz cavities, but the design allows a full upgrade to 1.3 GHz, envisioned in 2007. This setup, which incorporates several technological solutions that can be later transferred to the unit at Argonne, is now operational. The primary near-term goal is to continue testing small cavities, and six single-cell 3.9 GHz cavities will become available for this purpose. At the same time, this unit shall allow testing additional technical solutions for implementation into the Argonne unit. During FY07, this setup shall be scaled up to handle 1.3 GHz 1-cell cavities and support the newly established Fermilab single-cell program.

In order to introduce Niobium electropolishing to US industry, both local and national companies have been contacted. The initial goal of this activity is to establish a collaborative effort with possible developers of electropolishing units and possible companies that can reliably run the process.

In parallel with the facility activities, collaboration with Udine University in Italy has been established, and scientists are now applying a numerical approach to the modeling of the electropolishing process. The initial goal of defining the proper system of equations that describe the process has been completed.

A pilot small sample tumbling program, another technique for creating smooth cavity surfaces, has also been established at Fermilab. An experimental device has been designed and shall be operational in 2007. Several tests will be conducted to better understand the basics of the process and adaptation to the Niobium characteristics.

The fundamental understanding of electropolishing and the exploration of new acid mixtures, acid aging and F- concentration control shall continue to be intensified at Fermilab by increasing the number of small sample tests.

Americas 9-cell ILC S0 Cavities- Update