Outgassing Reductions via Quasi-Isentropic Ramp Compression: A Simulation Study

A collaborative effort between Texas Tech University and the University of New Mexico is studying the ways to suppress or minimize outgassing from anode materials in the context of high-power microwave devices. Outgassing can lead to plasma formation with several deleterious effects such as anode-cathode gap closure with impedance collapse, pulse shortening, phase shifts, reductions in system efficiency, and degradation in the longevity and reliability of HPM systems. Here, a possible solution strategy based on quasi-isentropic compression (QIC) is probed with quantitative predictions based on molecular dynamics (MD) simulations. Using copper with hydrogen gaseous impurity as an example anode, our results show that a strong and short pressure ramp applied at one surface can lead to a herding of hydrogen atoms towards the opposite face as well as lead to an initial outgassing and neutral load reduction. Such gaseous impurity gathering could then be used for driving off the impurities by additional surface treatment and cleaning. Additionally, it is shown that upon compression, the surface becomes denser and resistant to subsequent diffusive uptake of hydrogen adsorbates, thus affecting a surface seal. Similar analysis could be applied to other gases (or gas mixtures) as well such as mitigating outgassing of oxygen, CO and CO2 in metals.