Resonant pedestal pressure reduction induced by a thermal transport enhancement due to stochastic magnetic boundary layers in high temperature plasmas.

Good alignment of the magnetic field line pitch angle with the mode structure of an external resonant magnetic perturbation (RMP) field is shown to induce modulation of the pedestal electron pressure p(e) in high confinement high rotation plasmas at the DIII-D tokamak with a shape similar to ITER, the next step tokamak experiment. This is caused by an edge safety factor q95 resonant enhancement of the thermal transport, while in contrast, the RMP induced particle pump out does not show a significant resonance. The measured p(e) reduction correlates to an increase in the modeled stochastic layer width during pitch angle variations matching results from resistive low rotation plasmas at the TEXTOR tokamak. These findings suggest a field line pitch angle resonant formation of a stochastic magnetic edge layer as an explanation for the q95 resonant character of type-I edge localized mode suppression by RMPs.

Quiescent H-mode plasmas with strong edge rotation in the cocurrent direction.

For the first time in any tokamak, quiescent H-mode (QH-mode) plasmas have been created with strong edge rotation in the direction of the plasma current. This confirms the theoretical prediction that the QH mode should exist with either sign of the edge rotation provided the magnitude of the shear in the edge rotation is sufficiently large and demonstrates that counterinjection and counteredge rotation are not essential for the QH mode. Accordingly, the present work demonstrates a substantial broadening of the QH-mode operating space and represents a significant confirmation of the theory.

Porous plug gas injection systems for studies of hydrocarbon dissociation and transport in the DIII-D tokamak.

A probe has been designed, constructed, and successfully used to inject methane into the DIII-D lower divertor in a manner imitating natural release by chemical erosion. This porous plug injector (PPI) probe consists of a self-contained gas reservoir with an integrated pressure gauge and a 3 cm diameter porous surface through which gas is injected into the lower divertor of the tokamak. The probe is positioned flush with the divertor target surface by means of the divertor materials evaluation system. Two gas delivery systems were developed: in the first, gas flow is regulated by a remotely controlled microvalve and in the second by a fixed micro-orifice flow restrictor. Because of the large area of the porous surface through which gas is admitted, the injected hydrocarbon molecules see a local carbon surface (>90% carbon) similar to that seen by hydrocarbons being emitted by chemical sputtering from surrounding carbon tiles. The distributed gas source also reduces the disturbance to the local plasma while providing sufficient signal for spectroscopic detection. In situ spectroscopic measurements with the PPI in DIII-D allow the direct calibration of response for measured plasma conditions from a known influx of gas.

Dust measurements in tokamaks (invited).

Dust production and accumulation present potential safety and operational issues for the ITER. Dust diagnostics can be divided into two groups: diagnostics of dust on surfaces and diagnostics of dust in plasma. Diagnostics from both groups are employed in contemporary tokamaks; new diagnostics suitable for ITER are also being developed and tested. Dust accumulation in ITER is likely to occur in hidden areas, e.g., between tiles and under divertor baffles. A novel electrostatic dust detector for monitoring dust in these regions has been developed and tested at PPPL. In the DIII-D tokamak dust diagnostics include Mie scattering from Nd:YAG lasers, visible imaging, and spectroscopy. Laser scattering is able to resolve particles between 0.16 and 1.6 microm in diameter; using these data the total dust content in the edge plasmas and trends in the dust production rates within this size range have been established. Individual dust particles are observed by visible imaging using fast framing cameras, detecting dust particles of a few microns in diameter and larger. Dust velocities and trajectories can be determined in two-dimension with a single camera or three-dimension using multiple cameras, but determination of particle size is challenging. In order to calibrate diagnostics and benchmark dust dynamics modeling, precharacterized carbon dust has been injected into the lower divertor of DIII-D. Injected dust is seen by cameras, and spectroscopic diagnostics observe an increase in carbon line (CI, CII, C(2) dimer) and thermal continuum emissions from the injected dust. The latter observation can be used in the design of novel dust survey diagnostics.

Quiescent double barrier regime in the DIII-D tokamak.

A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases edge particle transport, thereby allowing particle control with no ELM-induced pulsed divertor heat load. The core barrier resembles those usually seen with a low (L) mode edge, without the degradation often associated with ELMs. The barriers are separated by a narrow region of high transport associated with a zero crossing in the E x B shearing rate.

Ultrastructure of cutaneous cellular infiltrates in scleroderma.

Electron microscopy of the skin was performed in ten patients with systemic and four with localized scleroderma. The following three groups of cells were identified: (1) mature lymphocytes, T lymphoblasts, immature plasma cells, and plasma cells; (2) fibroblasts, fibrocytes, and fibroblast-like cells; and (3) macrophages, undifferentiated mesenchymal cells, and monocytes. Inthose specimens with mononuclear cell infiltrates, the most common cells were lymphocytic-types, macrophages, and fibroblasts with well developed rough endoplasmic reticulum. In the specimens at the fibrotic stage, fibroblasts and histiocytic-type cells predominated. This study suggests that cellular and humoral immunity may play a role in the pathophysiology of scleroderma.