Synchrotron-based high-pressure research in materials science Page: 2 of 8
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Proceedings of American Society of Mechanical Engineers
International Design Engineering Technical Conference
Sep 28 -Oct 2 "2004, Salt Lake City UTAH
OPTIMIZATION OF CHEMICAL ETCHING PROCESS IN NIOBIUM CAVITIES
M. Trabia, W. Culbreth, S. Subramanian, T. Tajima*
Department of Mechanical Engineering
Howard R. Hughes College of Engineering
University of Nevada, Las Vegas
Las Vegas, NV 89154-4027
Tel: (702) 895-0957, Fax: (702) 895-3936, Email: mbt@me.unlv.edu
*Los Alamos National Laboratory, Los Alamos, NM 87545Abstract-Superconducting niobium cavities are important
components of linear accelerators. Buffered chemical
polishing (BCP) on the inner surface of the cavity is a standard
procedure to improve its performance. The quality of BCP,
however, has not been optimized well in terms of the uniformity
of surface smoothness. A finite element computational fluid
dynamics (CFD) model was developed to simulate the chemical
etching process inside the cavity. The analysis confirmed the
observation of other researchers that the iris section of the
cavity received more etching than the equator regions due to
higher flow rate. The baffle, which directs flow towards the
walls of the cavity, was redesigned using optimization
techniques. The redesigned baffle significantly improves the
performance of the etching process. To verbfy these results an
experimental setup for flow visualization was created. The
setup consists of a high speed, high resolution CCD camera.
The camera is positioned by a computer-controlled traversing
mechanism. A dye injecting arrangement is used for tracking
the fluid path. Experimental results are in general agreement
with CFD and optimization results.Alamos National Laboratory (LANL) is an active participant in
developing a high-current superconducting rf (SCRF) linear
accelerator. It has three major components: niobium cavities,
power couplers, and cryo modules. This paper principally
deals with niobium cavities.
Niobium cavities have several advantages including
significantly small power dissipation compared to copper
cavities due to the superconductivity. These cavities are
usually made of multiple elliptical cells, Figure 1. They are
formed from sheet metal using various techniques such as deep
drawing or spinning. The cells then are welded together using
electron-beams. Multi-cell units are usually tuned by stretching
or squeezing them.
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I. INTRODUCTION
The nuclear industry provides a significant percentage of
the world, as well as of the United States, with electricity.
Nuclear power plants produce thousands of tons of spent fuel.
Some of this spent fuel can be radioactive for thousands of
years. The US DOE is currently exploring the possibility of
creating a permanent storage site at Yucca Mountain, Nevada,
for spent nuclear fuel. The US Congress has recently authorized
exploring an alternative way to deal with spent nuclear fuel:
Accelerator Transmutation of Waste (ATW). In this approach,
a particle accelerator produces protons that react with a heavy
metal target to produce neutrons that hit spent fuel and shorten
the life of radioactivity through nuclear reactions. A major
component of the system is a linear accelerator (linac) that can
accelerate over 100 mA of protons to several GeV [1]. Losa.
Figure 1. A LANL APT Five-Cell Niobium Cavity Assembled
with Helium Vessels.
The performance of a niobium cavity deteriorates if its
surface has stains of chemical products on the surface.
Insufficient degreasing, liquid retention in pits, areas with
varying metal structure introduced during the manufacturing, orSa
1
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Synchrotron-based high-pressure research in materials science, article, Date Unknown; [Los Alamos, New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc926081/m1/2/: accessed May 13, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.