Completed 
          (June 2001-July 2005) 

 

Title  Modeling, Fabrication, and Optimization of Niobium Cavities	Researchers R.S. Schill, M.B.Trabia W. Culbreth, Collaborators Tsuyoshi Tajima, Team Leader, Accelerator Physics & Eng., LANSCE-1, Los Alamos National Laboratory
Background  One of the key technologies for the deployment of accelerator-driven transmutation systems is the accelerator itself.  Elliptical superconducting niobium cavities are used to increase the efficiency of the high-power accelerators needed to support the transmutation mission.    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 superconducting cavity and the accelerator.	Research Objectives and Methods This project was 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 objective of this study was to experimentally model the fluid flow resulting in the chemical etching of niobium cavities with the aid of a baffle.  Numerical analyses tend to show that the current etching process with a baffle does not uniformly etch the cavity surface. Multiple cavity cell geometries were investigated.  Optimization techniques were applied in search of the chemical etching processes, which would lead to cavity walls with near ideal properties.    A Monte Carlo secondary electron emission (SEE) code was modified to provide a statistical study of electron impact from Los Alamos National Laboratory (LANL) cleaned niobium samples at near cryogenic temperatures in an ultra high vacuum environment.  A one-of-a-kind secondary electron emission test stand was  developed to study, in part, the dynamics of the emitted particles subjected to an electron beam.  Coordinating code studies with experiments offers a wealth of knowledge regarding the surface physics of the material that can enhance modeling codes at LANL.  Modeling codes, optimization techniques, and experimentation provided UNLV researchers with a well-rounded study to examine existing and novel niobium cavity designs and cleaning processes for the superconducting radio frequency high-current accelerator. Side view of the secondary electron emission system.  The components from top to bottom are: electron gun end, electron beam tube,  particle position detector, micro-channel plate stack, business end of the manipulator arm, top of cryostat, and cryostat thermal guard.
Students  Sathishkumar Subramanian(G), Anoop George(G), Qin Xue(G) Myong Holl(U), Greg Loll(U)	Department Mechanical Engineering
Final Report  Final 08/01/05	Annual Report  Task 2 Year 1 Academic Year2001 Task 2 Year 2 Academic Year 2002
Proposal Final 04/13/01 Task 2 Year 2 Task 2 Year 3	Quarterly Reports  05/15/01-08/15/01 08/20/01-11/20/01 11/20/01-02/20/01 07/01/02-09/01/02 09/01/02-12/01/02 12/01/02-02/28/02 06/01/03-08/31/03 09/01/03-11/30/03 12/01/04-02/29/04 07/01/04-09/01/04 10/01/04-12/31/04 01/01/05-03/31/05
Papers Secondary Electron Emission From Niobium at Cryogenic Temperatures Optimization of Chemical Etching Process in Niobium Cavities   Modeling and Optimization of the Chemical Etching Process in Niobium Cavities Support Letter from Tsuyoshi Tajima (Los Alamos National Laboratory) Abstract Accelerator Applications in Nuclear Renaissance Conference  Prerparation Studies for Secondary Electron Emission Experiments on Superconducting Niobium	Researchers A. George, R. Schill, R. Kant S. Goldfarb S. Subramanian, Y. Chen, Q. Xue, M. Trabia, R. Schill   T. Tajima M. Holl, M. Trabia, R. Schill A. George, R. Schill

Thesis
M.S. Mechanical Engineering, Qin Xue, “Modeling and Simulation of the Chemical Etching Process in Niobium Cavities” Aug. 2002 (TRP Task 2)
M.S. Electrical Engineering, Anoop George, "Study of Secondary Electron Emission from Niobiom at Cryogenic Temperatures" Aug. 2005 (TRP Task 2 )
M.S. Mechanical Engineering, Satish Subramanian, “Modeling, Optimization, and Flow Visualization of Chemical Etching Process in Niobium Cavities,” May 2004 (TRP Task 2)

Posters
AFCI Semi-Annual Review Meeting Poster: An Analysis of the Melt Casting of  
 Metallic Fuel Pins-Jan 2003

Niobium Cavities (Department of Mechanical Engineering, UNLV) Website
Electromagnetics and Pulse Power Laboratories website