Reduction of edge-localized mode intensity using high-repetition-rate pellet injection in tokamak H-mode plasmas.

High repetition rate injection of deuterium pellets from the low-field side (LFS) of the DIII-D tokamak is shown to trigger high-frequency edge-localized modes (ELMs) at up to 12× the low natural ELM frequency in H-mode deuterium plasmas designed to match the ITER baseline configuration in shape, normalized beta, and input power just above the H-mode threshold. The pellet size, velocity, and injection location were chosen to limit penetration to the outer 10% of the plasma. The resulting perturbations to the plasma density and energy confinement time are thus minimal (<10%). The triggered ELMs occur at much lower normalized pedestal pressure than the natural ELMs, suggesting that the pellet injection excites a localized high-n instability. Triggered ELMs produce up to 12× lower energy and particle fluxes to the divertor, and result in a strong decrease in plasma core impurity density. These results show for the first time that shallow, LFS pellet injection can dramatically accelerate the ELM cycle and reduce ELM energy fluxes on plasma facing components, and is a viable technique for real-time control of ELMs in ITER.

Development of the materials analysis and particle probe for Proto-MPEX.

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a linear plasma device being used in plasma source research and development (R&D) for the proposed MPEX. Once the R&D is completed, this device can also be used to perform plasma-material interaction studies. To perform these studies, a new materials analysis and particle probe (MAPP) has been constructed. The MAPP's components are a sample holder and manipulator and a custom vacuum chamber with ports to facilitate surface chemistry diagnostics. The MAPP's overall design enables rapid sample turnaround and in vacuo surface characterization. The surface analysis vacuum chamber has ports for x-ray photoelectron spectroscopy, thermal desorption spectroscopy, back-scatter ion scattering spectroscopy, forward-scatter ion scattering spectroscopy, and direct recoil spectroscopy. The sample manipulator and holder is a Lesker/UHV Multi-Centre Analytical Stage, which is used to place the samples in the exposure region of the Proto-MPEX or the analysis position in the MAPP vacuum chamber. The sample holder has a heating capability of up to 1200 °C for heated exposure and for desorption studies. In this work, we present the MAPP's design and the first tungsten sample exposure with ex situ analysis that shows a surface deposition layer on the exposed target, highlighting the need for additional in situ measurements on the Proto-MPEX.

First results from the Thomson scattering diagnostic on proto-MPEX.

A Thomson scattering (TS) diagnostic has been successfully implemented on the prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory. The diagnostic collects the light scattered by plasma electrons and spectroscopically resolves the Doppler shift imparted to the light by the velocity of the electrons. The spread in velocities is proportional to the electron temperature, while the total number of photons is proportional to the electron density. TS is a technique used on many devices to measure the electron temperature (Te) and electron density (ne) of the plasma. A challenging aspect of the technique is to discriminate the small number of Thomson scattered photons against the large peak of background photons from the high-power laser used to probe the plasma. A variety of methods are used to mitigate the background photons in Proto-MPEX, including Brewster angled windows, viewing dumps, and light baffles. With these methods, first results were measured from argon plasmas in Proto-MPEX, indicating Te ∼ 2 eV and ne ∼ 1 × 1019 m-3. The configuration of the Proto-MPEX TS diagnostic will be described and plans for improvement will be given.

High-speed digital holography for neutral gas and electron density imaging.

An instrument was developed using digital holographic reconstruction of the wavefront from a CO2 laser imaged on a high-speed commercial IR camera. An acousto-optic modulator is used to generate 1-25 µs pulses from a continuous-wave CO2 laser, both to limit the average power at the detector and also to freeze motion from sub-interframe time scales. Extensive effort was made to characterize and eliminate noise from vibrations and second-surface reflections. Mismatch of the reference and object beam curvature initially contributed substantially to vibrational noise, but was mitigated through careful positioning of identical imaging lenses. Vibrational mode amplitudes were successfully reduced to ≲1 nm for frequencies ≳50 Hz, and the inter-frame noise across the 128 × 128 pixel window which is typically used is ≲2.5 nm. To demonstrate the capabilities of the system, a piezo-electric valve and a reducing-expanding nozzle were used to generate a super-sonic gas jet which was imaged with high spatial resolution (better than 0.8 lp/mm) at high speed. Abel inversions were performed on the phase images to produce 2-D images of localized gas density. This system could also be used for high spatial and temporal resolution measurements of plasma electron density or surface deformations.

Design of a digital holography system for PFC erosion measurements on Proto-MPEX.

A project has been started at ORNL to develop a dual-wavelength digital holography system for plasma facing component erosion measurements on prototype material plasma exposure experiment. Such a system will allow in situ real-time measurements of component erosion. Initially the system will be developed with one laser, and first experimental laboratory measurements will be made with the single laser system. In the second year of development, a second CO2 laser will be added and measurements with the dual wavelength system will begin. Adding the second wavelength allows measurements at a much longer synthetic wavelength.

Co-destructive factors of marginal periodontitis and repetitive mechanical injury.

When repetitive mechanical injury was produced in combination with marginal periodontitis a significant loss of connective tissue attachment did not occur as compared with specimens in which periodontitis alone was produced. It seems unlikely, therefore, that there is a "co-destructive" factor effect on the loss of connective tissue attachment. The amount of alveolar bone lost as a result of marginal periodontitis was increased by the addition of repeated mesiodistal jiggling of the teeth. This could represent an irreversible "co-destructive" effect or could merely be a functional adaptation of the periodontium.

Associations between crestal lamina dura and periodontal status.

The purpose of the present study was to investigate associations between radiographic crestal lamina dura and the clinical periodontal status of the corresponding interdental area. The population consisted of 90 individuals (53 females and 37 males), ages 21 to 45 years (mean 31 years), who underwent a comprehensive periodontal examination. Buccal and lingual to the contact point at each interdental area four different clinical criteria were scored as being present or absent: (i) visual inflammation, (ii) bleeding after probing with 25 gm force, (iii) pocket depth greater than 3 mm after probing with 50 gm force, (iv) loss of connective tissue attachment. Bite-wing and full-mouth periapical radiographs were taken and processed using standardized techniques. Each interdental crestal area on the radiographs was examined and scored for presence or absence of an intact lamina dura. Statistical analyses were undertaken using correlated means to compare the presence or absence of lamina dura with the individual and simultaneous clinical criteria. No significant differences were obtained between any of the comparisons and, in addition, there was no correlation between lamina dura images on periapical and bite-wing radiographs. The results indicated that crestal lamina dura on radiographs did not appear to be related to the presence or absence of clinical inflammation, bleeding upon probing, periodontal pockets or loss of attachment.

A periodontal attachment mechanism without alveolar bone. Case report.

A 22-year-old black male was referred for periodontal therapy because of radiographic evidence of advanced bone loss associated with the posterior teeth. Clinical examination revealed gingivitis, normal sulcus depths, and minimal loss of clinical attachment. Complete blood counts, serum chemistry, and neutrophil function were within normal limits. Histological, histochemical and ultrastructural analysis of an extracted tooth revealed no loss of attachment; large areas of the cementum were collagen-poor and, ultrastructurally, resembled afibrillar cementum. It is proposed that the periodontal attachment mechanism present in this case was associated with a localized failure in normal periodontal development.

Comparison between planned prosthetic trajectory and residual bone trajectory using surgical guides and tomography--a pilot study.

Implant treatment is a highly technical and complex form of dentistry. Research and experience have shown that the success of dental implant treatment relies on a well-developed treatment plan approach that takes into account factors such as systemic condition, anatomical landmarks, occlusion, shape and density of the jawbone, and type of implant system. Historically, once the tissue was reflected, implant placement was guided by residual bone height and width, using the trajectory that was compatible with the location and direction of available bone, at times compromising prosthetic needs. The purpose of this study was to measure the amount of deviation between planned prosthetic trajectory (PPT), perpendicular to the plane of occlusion, and residual bone trajectory (RBT) in different areas of the maxillary and mandibular dental arches, using tomography in conjunction with surgical guides. Twenty-five patients with a total of 66 implant sites were selected for this study. A surgical guide with a radiopaque indicator was constructed to determine the PPT. Cross-sectional tomograms were taken through the indicator at each implant site. The outlines of the available bone, PPT and RBT, were traced, and the difference in the angulation between the two trajectories was determined. Results showed discrepancies between the PPT and the RBT to be greater in the mandibular molar areas. Further study of such pre-implant diagnostic procedures is needed to understand the relation between the PPT and RBT, thus increasing the predictability of implant success.

Fast imaging of intact and shattered cryogenic neon pellets.

Compact condensed-matter injection technologies are increasingly used in magnetic fusion. One recent application is in disruption mitigation. An imaging system with less-than-100-µm- and sub-µs-resolution is described and used to characterize intact and shattered cryogenic neon pellets. Shattered pellets contain fine particles ranging from tens of µm to about 7 mm. Time-of-flight analyses indicate that pellets could slow down if hitting the wall of the guide tube. Fast high-resolution imaging systems are thus useful to neon and other condensed-matter injector development.

Digital holography for in situ real-time measurement of plasma-facing-component erosion.

In situ, real time measurement of net plasma-facing-component (PFC) erosion/deposition in a real plasma device is challenging due to the need for good spatial and temporal resolution, sufficient sensitivity, and immunity to fringe-jump errors. Design of a high-sensitivity, potentially high-speed, dual-wavelength CO2 laser digital holography system (nominally immune to fringe jumps) for PFC erosion measurement is discussed.

High speed digital holography for density and fluctuation measurements (invited).

The state of the art in electro-optics has advanced to the point where digital holographic acquisition of wavefronts is now possible. Holographic wavefront acquisition provides the phase of the wavefront at every measurement point. This can be done with accuracy on the order of a thousandth of a wavelength, given that there is sufficient care in the design of the system. At wave frequencies which are much greater than the plasma frequency, the plasma index of refraction is linearly proportional to the electron density and wavelength, and the measurement of the phase of a wavefront passing through the plasma gives the chord-integrated density directly for all points measured on the wavefront. High-speed infrared cameras (up to ∼40,000 fps at ∼64×4 pixels) with resolutions up to 640×512 pixels suitable for use with a CO(2) laser are readily available, if expensive.

Surgical templates for prosthetically guided implant placement.

The article describes a prosthetically guided method for the fabrication of surgical templates for partially edentulous patients. A number of stainless steel components are used to capture the optimal prosthetic position for the placement of the implant determined from a diagnostic arrangement. A radiopaque stainless steel guide sleeve is used to guide the drill in preparation of the osteotomy after radiographs are made to verify the position and proposed trajectory of the guide sleeve.

Oral and esophageal Candida albicans infection in hyposalivatory rats.

The opportunistic fungus Candida albicans is a major cause of oral and esophageal infections in immuno-compromised patients, individuals on drug therapy, and the chronically ill. Because it has been observed that persons suffering from hyposalivation have an increased prevalence of oral candididiasis, we developed an animal model of infection based on hyposalivation. The objectives of our studies were to understand the mechanisms by which C. albicans causes oral disease and to begin to elucidate the role played by saliva in controlling C. albicans in the oral cavity. Our results showed that (i) oral Candida infection was established by a small challenge inoculum, (ii) mucosal lesions developed in the oral cavities and esophagi of infected rats, and (iii) transmission of oral Candida infection from an inoculated rat to uninoculated cagemates occurred rapidly. In addition, we compared the abilities of a clinical isolate and a spontaneously derived morphological mutant from that isolate to infect hyposalivatory rats and to induce disease. Infection was induced by the morphological mutant in hyposalivatory rats; however, the morphological mutant took significantly longer to transmit oral infection to uninoculated cagemates than did the parental strain.

Fabrication of imaging and surgical guides for dental implants.

Research and experience have suggested that the success of dental implants depends on a well-developed and careful treatment plan approach. Historically, implant size and angulation were determined with the use of panoramic radiographs and clinical judgment during surgery. This occasionally resulted in mechanical and esthetic compromise. This article describes the step-by-step fabrication process for 4 different imaging and surgical guides. Set-up disks, which enhance the design and fabrication of guides, also are introduced. These guides are used in conjunction with cross-sectional tomography during the preimplant assessment of surgical sites.

Long-term periodontal status after orthodontic treatment.

This study evaluated the clinical periodontal status of persons who had completed orthodontic therapy at least 10 years previously (study) and compared the findings to those of adults with untreated malocclusions (control). Subjects in the study (n = 112; 63 female subjects, 49 male subjects; mean age 29.3 +/- 4.2 [SD] years) and control (n = 111; 62 female subjects, 49 male subjects; mean age 32.9 +/- 6.5 years) populations underwent a comprehensive periodontal examination that consisted of measurements taken at six points around the circumference of each tooth: (1) plaque, (2) visual inflammation, (3) bleeding after probing, (4) pocket depth, (5) gingival recession, and (6) loss of connective tissue attachment. Data from the individual measuring points were organized into 14 different combinations of either tooth types or surface locations; each was subjected to a four-way ANOVA partitioned on group (study vs. control), sex, socioeconomic status, and malocclusion type. The results showed that differences in age distribution within the groups were affecting the comparisons between the groups. Consequently, the groups were balanced for age and analyses were done to investigate group differences by means of multiple regression techniques. The comparisons showed no significant differences between the groups for any of the periodontal variables. It was concluded that orthodontic treatment during adolescence had no discernible effect upon later periodontal health.