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09 Dec 2011

Cost Benefits of Centrifugally Cast 316L Stainless Steel in Continuous Electron Beam Accelerator

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Application Assessment at Thomas Jefferson National Laboratory (JLAB) in Newport News, Virginia, USA.by Alan Holtz, VP – Sales & Engineering, Spuncast
Presented December 2011

ABSTRACT

In mid-2007, Spuncast, Inc. was contacted by the Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, Virginia, USA to participate in a cost-reduction effort specific to the C100 Helium Vessels. The helium vessels are part of the electron path of the accelerator. The original design of the vessels used titanium as the primary material of construction. Additionally, there were welded joints between the niobium sections and titanium portions of the assembly. If some of the titanium sections could be replaced with ASME SA351 Grade CF3M (cast 316L stainless steel) significant cost savings could be realized.

The part chosen was a section of the C100 cryomodule’s Helium Vessel Head.
To prove out the feasibility of this conversion, numerous criteria needed to be met. First, the part was required to be completely leak-tight with liquid helium on one side and a vacuum of 10-9 torr on the other. In the presence of liquid He (temperature of 2°K) the material needed to exhibit sufficient strength and ductility to support 5 atm of internal pressure and 2 atm of external pressure. Fabricability had to allow for a niobium to SS transition.

The testing was done at the Jefferson test facility on their HTB (Horizontal Test Bed – a facility for testing up to two cavities with cryomodule boundary conditions). Validation was determined by thermal shock, thermal cycling, pressure testing and actual function testing. In all cases, the centrifugally cast member passed with ease.

While Spuncast continues to supply this part for TJNAF, it is interesting to surmise what could be possible utilizing the economy of the centrifugal casting process in stringent soundness applications, most notably, a wide variety of vacuum applications.

SUMMARY

The 12GeV upgrade project holds a wealth of new opportunities for the nuclear physics community. The doubling of the electron beam’s energy will allow a whole new set of experimental parameters to be utilized in the continuing search for the origins of matter. As Jefferson Lab embarked on their massive upgrade project, they needed to find new ways to construct the cryomodules that afforded cost reductions without any sacrifice in quality or functionality. The use of centrifugal castings for the helium vessel heads, while a relatively small savings in the overall project, shows the open-mindedness of the designers of the new equipment.

The success of this project brings to mind additional applications. The JLAB application is quite severe in terms of not only atmosphere, where temperature and vacuum are extreme, but also regarding the medium’s molecular size. With a vacuum of 10-7 torr actually surrounding the outside of the CF3M vessel head and the very small molecules of the liquid helium on the inside, many engineers would worry about the use of castings. Centrifugal castings have proven exceptionally capable of functioning very well. It is very possible to surmise that centrifugal castings can be used in a wide variety of other vacuum applications where pressure tightness is critical to successful operation of the finished product.

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Continuous Electron Beam Accelerator White Paper Collage
Photos and Diagrams from Presentation.
From top to bottom: (1) pressure test fixture for SS vessel head, (2) JLab linear assembly section, (3) closeup of vessel head prototype details and (4) current CEBAF schematic.

Alan Holtz VP Sales EngineeringAlan Holtz

ACADEMIC PROFILE:
Bachelor of Arts: History
University of Pennsylvania, Philadelphia, PA, USA

Bachelor of Science – Metallurgical Engineering, University of Missouri-Rolla, Rolla, MO, USA

CURRENT POSITION:
Vice President, Sales & Engineering
Spuncast, Inc.
Watertown, WI USA

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