Graham Wright

In situ elastic recoil detection analysis of tungsten surfaces during ITER-like helium irradiation

Tungsten surfaces are subjected to helium plasma simulating a tokamak divertor environment in the Dynamics of ION Implantation and Sputtering Of Surfaces (DIONISOS) experiment. For this work, surfaces are analyzed in real-time during irradiation with in situ elastic recoil detection to gain dynamic helium concentration depth profiles. The extreme environment of the divertor simulator requires specific considerations to be implemented to retain the integrity of Ion Beam Analysis (IBA) techniques for surface analysis. The development of the in situ elastic recoil detection measurement technique and the implications of the results regarding the modeling of tungsten surface modification due to helium plasma irradiation will be discussed.

Broad ion energy distributions in helicon wave-coupled helium plasma

Helium ion energy distributions were measured in helicon wave-coupled plasmas of the dynamics of ion implantation and sputtering of surface experiment using a retarding field energy analyzer. The shape of the energy distribution is a double-peak, characteristic of radiofrequency plasma potential modulation. The broad distribution is located within a radius of 0.8 cm, while the quartz tube of the plasma source has an inner radius of 2.2 cm. The ion energy distribution rapidly changes from a double-peak to a single peak in the radius range of 0.7–0.9 cm. The average ion energy is approximately uniform across the plasma column including the double-peak and single peak regions. The widths of the broad distribution, ΔE, in the wave-coupled mode are large compared to the time-averaged ion energy, ⟨E⟩. On the axis (r = 0), ΔE/ ⟨E⟩ ≲ 3.4, and at a radius near the edge of the plasma column (r = 2.2 cm), ΔE/ ⟨E⟩ ∼ 1.2. The discharge parameter space is scanned to investigate the effects of the magnetic field, input ...

Ion implantation for figure correction of thin X-ray telescope mirror substrates

Figure correction of X-ray telescope mirrors will be critical for future missions that require high angular resolution and large collecting areas. In this paper, we show that ion implantation offers a method of correcting figure errors by imparting sub-surface in-plane stress in a controllable magnitude and location in Schott D-263 glass, Corning Eagle XG glass, and crystalline silicon substrates. In addition, we can in theory achieve nearly exact corrections in Schott D-263 glass, by controlling the direction of the stress. We show that sufficient stress may be applied to Schott D-263 glass to achieve figure correction in mirrors with simulated initial figure errors. We also report on progress of a system that will be capable of correcting conical shell mirror substrates.

Gas bearing slumping and figure correction of x-ray telescope mirror substrates

Figure correction of thin x-ray telescope mirrors may be critical for future missions that require high angular resolution and large collecting areas. One promising method of providing figure correction is to use stress generated via ion implantation. Since stress-based figure correction strategies cannot correct high spatial frequency errors, it is critical to obtain glass with only low spatial frequency error. One method is thermal gas bearing slumping, where glass is softened while floating on thin films of gas. This method avoids introducing mid- or high- spatial frequency errors by eliminating contact between the glass and mandrel. Together, these two methods form a promising approach to fabricating mirrors for a high angular resolution, large-area x-ray observatory. In this paper we report on progress in understanding gas bearing slumping, and advancing the technology to curved geometry. We also report on continued progress on advancing the ion implantation technology toward correcting flight-sized mirror substrates.

Plasma Surface Interaction (PSI) studies at DIII-D

Understanding of Plasma Surface Interactions (PSI) and the selection of suitable plasma facing materials are critical areas for current tokamak experiments and future D-T burning facilities including ITER and FNSF. In support of PSI studies, DIII-D uses the Divertor Materials Evaluation System (DiMES), which contains a removable probe where material samples can be exposed to as few as a single well-characterized plasma shot. Experiments, consisting of a carbon DiMES probe surface with metal coatings of Be, W, V, Mo or Al, have been exposed to the DIII-D lower divertor strike point plasma for cumulative discharge times of 4-20s. Extensive DIII-D divertor diagnostics provided well-characterized plasmas for modeling efforts. Experimental results were benchmarked with modeling codes to validate and extend the predictive capability of the codes. Reported in this paper are two recent experiments and results. The first is on the net and gross erosion of Mo coatings and the extension of these results to an extrapolated all Mo surface DIII-D machine. The second is on the exposure to vertical displacement discharges and X-point plasma discharges of W-fuzz buttons, which were prepared by the PISCES (UCSD) laboratory. The surprising results are the robustness of the W-fuzz and that W impurity was not detected in the plasma core at the conditions studied.