AVS 45th International Symposium
    Vacuum Technology Division Wednesday Sessions
       Session VT-WeA

Invited Paper VT-WeA3
An Ultra-High Vacuum System for Hydriding Rare Earth Metal Films

Wednesday, November 4, 1998, 2:40 pm, Room 329

Session: Vacuum Systems and Components
Presenter: S.J. Black, Los Alamos National Laboratory
Authors: S.J. Black, Los Alamos National Laboratory
F.J. Steinkruger, Los Alamos National Laboratory
C.W. Walthers, Los Alamos National Laboratory
Correspondent: Click to Email
Los Alamos National Laboratory has designed, fabricated, assembled and tested a state-of-the-art vacuum system for the hydriding of reactive rare earth metal films. The application of this system is dihydriding 5000Å erbium films on molybdenum substrates for neutron tubes. Neutron tubes are a major component of neutron generators, which are used in modern nuclear weapons. The system is capable of achieving pressures in the 10@super -10@ torr range. Such pressures are desirable in order to reduce contaminant gas species (which would otherwise compete with the hydriding reaction), to the parts per billion level. The vacuum is provided by oil-free turbomolecular/molecular drag pumps. Rough pumping is provided by a scroll pump backed by a metal bellows pump. In order to achieve these low pressures, measures were taken in the design and operation of the system. In order to reduce outgassing within the system, we eliminated all organic material within the system through the use of all-metal valves. All fittings are either welded or rely on metal O-rings. Passivation of the vacuum system interior surfaces was performed to reduce condensation of oxygen and water on the stainless steel surfaces. Other materials used within the vacuum system (film substrates, fixtures, and radiation shields) are made of molybdenum which is extensively cleaned prior to use. The loader system is capable of heating the films to 700°C while under vacuum, and continuing to maintain those temperatures after adding several hundred torr of hydrogen isotopes or inert purge gases to the system. Since the vacuum system is opened each time films are either loaded or removed from the vacuum chamber, the apparatus is installed within an inert (nitrogen) glovebox. Remote operation of the system is made possible through the use of pneumatically-actuated valves. The system is heavily instrumented in order to achieve tight process control. Two residual gas analyzers (RGA's) are used to determine the chemical composition of species within the system during evacuation. Details of the hardware design will be presented as well as performance data.