AVS 64th International Symposium & Exhibition
    Vacuum Technology Division Monday Sessions
       Session VT-MoA

Paper VT-MoA4
Automatic Flowmeter and Dynamic Expansion System for UHV/XHV Studies

Monday, October 30, 2017, 2:40 pm, Room 7 & 8

Session: Material Outgassing, Adsorption/Desorption and XHV
Presenter: James Fedchak, NIST
Authors: J.A. Fedchak, NIST
J. Scherschligt, NIST
D. Barker, NIST
S. Eckel, NIST
Correspondent: Click to Email
NIST is presently creating the Cold Atom Vacuum Standard (CAVS), a quantum-based fundamental primary vacuum sensor which significantly departs from present methods of measuring and realizing ultra-high vacuum (UHV) and extreme-high vacuum (XHV). The CAVS is an absolute sensor based on the loss-rate of ultra-cold atoms from a conservative magnetic trap due to collisions of the trapped cold atoms with the ambient background gas, and will cover a pressure range of 10-8 torr to below 10-12 torr, thus spanning UHV and into XHV. Knowledge of the thermalized collision cross-section, or loss-rate coefficient, between the trapped ultra-cold sensor atoms and the background gas is critical to operation of the CAVS; such collisions are also important in other experiments and devices based on trapped cold atoms because they limit the lifetime of atoms in the trap and, in addition, glancing collisions can increase statistical and other uncertainties. To support the CAVS and other atomic physics programs, NIST is developing a dynamic expansion system to set a known pressure in the CAVS, which will allow the experimental determination of collision cross-sections, relative gas-sensitivity factors, and facilitate studies of other systematic effects. To that end, we are developing a constant pressure flowmeter capable of producing flows of at least 10-13 mol/s and a dynamic expansion system to produce pressure rises as small as 10-10 Pa. The system is designed to produce low gas-flows of H2 and many other gases of interest, to be fully automated, and to have extremely low outgassing rates. The design and construction of the UHV/XHV flowmeter and dynamic expansion system will be discussed.