This report summarizes the accomplishments of a Laboratory-Directed Research and Development (LDRD) project focused on developing and applying new x-ray spectroscopies to understand and improve electric charge transfer in electrochemical devices. Our approach studies the device materials as they function at elevated temperature and in the presence of sufficient gas to generate meaningful currents through the device. We developed hardware and methods to allow x-ray photoelectron spectroscopy to be applied under these conditions. We then showed that the approach can measure the local electric potentials of the materials, identify the chemical nature of the electrochemical intermediate reaction species and determine the chemical state of the active materials. When performed simultaneous to traditional impedance-based analysis, the approach provides an unprecedented characterization of an operating electrochemical system.
Quantifying the flux and energy of charge exchange neutrals to the walls of fusion experiments is important to understanding wall erosion and energy balance. Quantification of these fluxes is made much more difficult because they have very strong poloidal and toroidal variations. To facilitate such measurements, we have been developing compact, palladium metal oxide semiconductor (Pd-MOS) detectors. These devices are dosemetric detectors, which can evaluate differences between plasma discharges. To become widely used, however, such detectors must be made resistant to UV and x-ray induced damage, as well as high energy particle bombardment. We report here on the fabrication of Schottky diode Pd-MOS devices in which we have minimized the oxide thickness (to reduce the production of charges from UV and x-rays) and increased the Pd overlayer (to reduce charge production from high energy particles). The fabrication has been facilitated through use of an array of metallic posts to improve the Pd film adhesion. The efficacy of the film adhesion and comparison with standard detectors will be examined. Testing and calibration of the detectors is reported as a function of hydrogen flux and energy.
Overview of Plasma Materials Interaction (PMI) activities are: (1) Hydrogen diffusion and trapping in metals - (a) Growth of hydrogen precipitates in tungsten PFCs, (b) Temperature dependence of deuterium retention at displacement damage, (c) D retention in W at elevated temperatures; (2) Permeation - (a) Gas driven permeation results for W/Mo/SiC, (b) Plasma-driven permeation test stand for TPE; and (3) Surface studies - (a) H-sensor development, (b) Adsorption of oxygen and hydrogen on beryllium surfaces.
The energies of adsorbed H and D recoiled from tungsten surfaces during bombardment with 3 keV Ne{sup +} at oblique angles of incidence were measured. The energy spectra show structure that extends above the elastic recoil energy. We find that the high-energy structure results from multiple collisions, namely recoil of a H isotope followed by scattering from an adjacent W atom, and vice versa. This scattering assisted recoil process is especially prevalent for H isotopes adsorbed on W, owing to the large mass difference between the scattering partners. Such processes will tend to enhance H isotope recycling from plasma-facing W surfaces and reduce energy transfer to the W substrate.
