University of Nevada, Las Vegas. Department of Mechanical Engineering.
Las Vegas (Nev.)
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One of the key technologies for the deployment of accelerator driven transmutation systems is the accelerator itself. To increase the efficiency of the high-power accelerators needed to support the transmutation mission, the national and international accelerator teams have proposed using elliptical superconducting niobium cavities. This project is tasked with examining the impacts of the design and fabrication technologies for these elliptical niobium cavities on their performance. Niobium was selected primarily due to its behavior at low temperatures.
One of the major sources of energy loss from a superconducting accelerator cavity is a process known as multiple impacting (or “multipacting”) of electrons. This phenomenon limits the maximum amount of energy and power that the niobium cavity can store. As a result, the maximum power available for accelerating the desired charge, as well as the overall performance of the accelerator is reduced. Furthermore, the energy absorbed as a result of multipacting eventually turns into heat. This negatively impacts the performance of both the super conducting cavity and the accelerator.
Multipacting is effected by the surface properties of the niobium wall. This is usually described in terms of the secondary electron emission coefficient. The presence of chemical products or foreign particles on the surface of the cavity undesirably impacts this coefficient. To help reduce this potential source of multipacting, the cavity walls are polished after manufacturing using chemical etching and high pressure rinsing. However, these chemical etching processes can result in non-uniform cavity surfaces with some unclean areas with contaminants and micron size particles. These imperfections significantly affect multipacting. Further, a non-uniform etch leaves areas with damaged grain structure.
These defects further reduce the superconducting properties of the niobium. Researchers at Los Alamos National Laboratory (LANL) employ a baffle to improve uniformity in the etching process. The baffle’s ability to improve the uniform etching was not known a priori.
Mitigating multipacting processes is the major concern dictating the elliptical shape of the superconducting cavity. This complicates the etching process and, in particular, the uniform etch. Modeling codes, optimization techniques, and experimentation will provide UNLV researchers with a well-rounded study to examine existing and novel niobium cavity designs for the superconducting radio frequency high-current accelerator.
Elliptical cells; Holes; Linear accelerators; Niobium cavities; Niobium – Surfaces; Radio frequency; Resonant radio frequency; Surface preparation; Surfaces (Technology); Superconducting radio frequency; Superconductivity
Linear accelerators; Radio frequency; Superconductivity
Electrical and Computer Engineering | Mechanical Engineering | Metallurgy | Nuclear Engineering
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Schill, R. A.,
Modeling, Fabrication, and Optimization of Niobium Cavities.
Available at: https://digitalscholarship.unlv.edu/hrc_trp_sciences_materials/17