A one dimensional, absolutely calibrated pinhole camera system was installed on the DIII-D tokamak to measure edge Lyman-alpha (Ly-α) emission from hydrogen isotopes, which can be used to infer neutral density and ionization rate profiles. The system is composed of two cameras, each providing a toroidal fan of 20 lines of sight, viewing the plasma edge on the inboard and outboard side of DIII-D. The cameras’ views lie in a horizontal plane 77 cm below the midplane. At its tangency radius, each channel provides a radial resolution of ∼2 cm full width at half maximum (FWHM) with a total coverage of 22 cm. Each camera consists of a rectangular pinhole, Ly-α reflective mirror, narrow-band Ly-α transmission filter, and a 20 channel AXUV photodetector. The combined mirror and transmission filter have a FWHM of 5 nm, centered near the Ly-α wavelength of 121.6 nm and is capable of rejecting significant, parasitic carbon-III (C-III) emission from intrinsic plasma impurities. To provide a high spatial resolution measurement in a compact footprint, the camera utilizes advanced engineering and manufacturing techniques including 3D printing, high stability mirror mounts, and a novel alignment procedure. Absolutely calibrated, spatially resolved Ly-α brightness measurements utilize a bright, isolated line with low parasitic surface reflections and enable quantitative comparison to modeling to study divertor neutral leakage, main chamber fueling, and radial particle transport.

The plasma and neutral density dynamics after an Edge Localized Mode (ELM) are investigated and utilized to infer the plasma transport coefficients for the density pedestal. The LLAMA diagnostic provides sub-millisecond profile measurements of the ionization and neutral density and shows significant poloidal asymmetries in both. Exploiting the absolute calibration of the LLAMA diagnostic allows quantitative comparison to the electron and main ion density profiles determined by charge-exchange recombination, Thomson scattering and interferometry. Separation of diffusion and convection contributions to the density pedestal transport are investigated through flux gradient methods and time-dependent forward modeling with Bayesian inference by adaptation of the Aurora transport code and IMPRAD framework to main ion particle transport. Both methods suggest time-dependent transport coefficients and are consistent with an inward particle pinch on the order of 1ms−1 and diffusion coefficient of 0.05m2 s−1 in the steep density gradient region of the pedestal. While it is possible to recreate the experimentally observed phenomena with no pinch in the pedestal, low diffusion in the core and high outward convection in the near scrape-off layer are required without an inward pedestal pinch.

Low-energy~electron-loss spectroscopy is used to study collective surface excitations on accumulation layers on ZnO. A prominent loss peak is observed which shifts in energy with electron concentration. The results are well accounted for theoretically and provide direct evidence for the existence of two-dimensional plasmons.PACS numbers: 71.45.Gm, 73, 79.20.Kz The elementary collective excitations of solid surfaces play a fundamental role in a number of recently discovered phenomena. These include some novel device applications like the generation of far-infrared radiation,^ surface photochemistry,^ and surface-enhanced adsorbate spectroscopy.^ The primary tools for probing such excitations have been optical. While optical spectroscopy yields excellent energy resolution, its spatial resolution is limited by its wavelength. In this Letter we report a study of surface excitations by low-energy-electron-loss spectroscopy (LEELS). We present experimental data for LEELS on ZnO surfaces and interpret the data theoretically. The surface properties of ZnO are changed by varying the electron density in the accumulation layer. The elementary excitations consist of coupled two-dimensional (2D) plasm on and phonon modes.The possibility of 2D plasmas in quantized space-charge layers was first pointed out by Stern"* in 1967, but their detection was found to be experimentally quite difficult. To attain the quantized space-charge layers one usually works with the silicon metal-oxide-semiconductor (MOS) structure, where the silicon is not very amenable to direct exterior probes. Thus experimental evidence for the existence of 2D plasmons on MOS structures was found only recently.^'^ LEELS was developed"^ to probe the electronic excitations at the surface and is natural for the study of 2D plasmas, provided that one can produce a quantized space-charge layer on difree surface. We performed our measurements on ZnO surfaces, one of the few semiconductors where quantized accumulation layers on the free surface can be obtained with relative ease.^"^° Our preliminary results^^ contained a coarse background in the energy-loss spectra which was attributed to scattering by 2D plasmons. The present improved data show a pronounced peak due to the plasmons. The energy of the peak increases monotonically with the surface electron concentration N^. Measurements were performed up to 2^3^2x10^^ cm"^, about an order of magnitude higher than on silicon.The theory of 2D plasmas in ZnO-a polar crystal-is somewhat more complicated than in silicon. The plasmon mode couples to the surface and bulk phonon modes and forms three hybrid branches, termed plasmarons .^^ Some theoretical studies of electron scattering from solid surfaces have appeared in the literature.'^ In our previous work^^ we developed a theory for ZnO in which the coupling to the plasmaron modes of the surface was manifest. A number of approximations were made, however, making a detailed comparison between theory and experiment difficult. These limitations have now been removed. Thus...