In April 2010, two thermo-oxidation experiments (‘O-bakes’) were performed in the DIII-D tokamak. Internal surfaces of the tokamak, as well as a number of specimens inserted into the torus, were exposed to a mixture of 20% O2/80% He at a nominal pressure of 9.5 Torr (1.27 kPa) at a temperature of 350–360 °C for a duration of 2 h. Three primary conclusions have been drawn from these experiments: (1) laboratory measurements on the release of deuterium from tokamak codeposits by oxidation have been duplicated in a tokamak environment, (2) no internal tokamak components or systems were adversely affected by the oxidation and (3) the recovery of plasma performance following oxidation was similar to that following regular torus openings.

Thermo-oxidation is controlled exposure in an oxygen-containing atmosphere at elevated temperature and is being considered as a technique for the detritiation of carbon-based codeposits in ITER. In addition, unplanned oxidation may also occur during accidental air ingress. The impact of thermo-oxidation on ITER diagnostic mirrors causes concerns. A dedicated study was performed in DIII-D, where molybdenum and copper mirrors were installed in the main chamber, in the divertor, and at a location remote from the plasma and exposed for similar to 2 hours to a mixture containing 80% helium and 20% oxygen at a total pressure of 1.27 kPa. Mirrors in the main chamber and in the divertor were exposed at 350 degrees C to 360 degrees C whereas the temperature of mirrors in the remote area was similar to 160 degrees C.Reflectivity of all mirrors was degraded after the thermo-oxidation showing a decrease in the UV range from 60% to 10% for molybdenum mirrors and a 90% drop for copper mirrors at the wavelength 250 nm. The reflectivity of mirrors exposed at lower temperature was less degraded. Surface analyses revealed formation of oxides on all mirrors.In ITER, shutters planned for mirror protection are ineffective against thermo-oxidation. Nevertheless, in-situ cleaning systems planned for ITER mirrors may efficiently remove oxide layers.

A series of DIII-D experiments was performed to investigate the potential for initiating plasma current using only poloidal field coils located outside the DIII-D central solenoid, i.e. ‘solenoid-free’. Plasma current to 166 kA was achieved using 2–3 MW of electron cyclotron (EC) heating and was limited by coil and power supply constraints. Flux conversion to plasma current was similar to standard DIII-D startup with some degradation at higher plasma current associated with stray fields and vertical stability issues. In preliminary solenoid-free experiments, neutral beam (NB) current drive (CD) levels were small and attributed to reduced CD efficiency associated with low electron temperature produced by the low current, low confinement plasma. Lack of plasma radial position control also contributed to a reduction of NBCD. Similarly, ECCD was small owing to low plasma temperature and outside EC launch which is required in the solenoid-free scenario. Synergistic experiments were carried out using standard solenoid initiated plasmas in order to study noninductive CD in limited, Lmode plasmas, typical of that generated by solenoid-free startup. While substantial noninductive current can be driven, self-sustaining levels of noninductive current have not yet been achieved with our present six-source co-injection NB system combined with EC and fast wave systems. At low plasma current and high levels of localized EC heating, substantial MHD is generated and this was seen to severely limit plasma performance. Although further optimization is possible in the limited plasma regime, full noninductive, steady-state operation may require diverted plasma with H-mode quality confinement. Discharges obtained during the solenoid-free campaign are compared with results of previous DIII-D campaigns aimed at achieving a steady state, noninductive CD solution.

An experiment was conducted in DIII-D to examine carbon deposition when a secondary separatrix is near the wall. The magnetic configuration for this experiment was a biased double-null, similar to that foreseen for ITER. C-13 methane was injected toroidally symmetrically near the secondary separatrix into ELMy H-mode deuterium plasmas. The resulting deposition of C-13 was determined by nuclear reaction analysis. These results show that very little of the injected C-13 was deposited at the primary separatrix, whereas a large fraction of injected C-13 was deposited close to the point of injection near the secondary separatrix. Six of the tiles were put back into DIII-D, where they were baked at 350-360 degrees C for 2 h at similar to 1 kPa in a 20% O-2/80% He gas mixture. Subsequent ion beam analysis of these tiles showed that about 21% of the C-13 and 54% of the deuterium were removed by the bake.

A series of DIII-D experiments was performed to investigate the potential for initiating plasma current using only poloidal field coils located outside the DIII-D central solenoid, i.e. “solenoid-free”. Plasma current to 170 kA was achieved using 2-3 MW of electron cyclotron (EC), heating and was limited by coil and power supply constraints. Flux conversion to plasma current was similar to standard DIII-D startup with some degradation at higher plasma current. In preliminary experiments, neutral beam (NB) current drive (CD) levels were small, partially due to lack of plasma radial position control. ECCD was small owing to low temperature and outside EC launch. Synergistic experiments were carried out using standard solenoid initiated plasmas to study noninductive current drive in limited, L-mode plasmas, typical of that generated by solenoid-free startup. While substantial noninductive current can be driven, self-sustaining levels of noninductive current have not yet been achieved with our present 6-source co-injection NB system combined with EC and fast waves. At low plasma current substantial MHD is generated at high levels of EC and this severely limits plasma performance. Although further optimization is possible in the limited plasma regime, full noninductive, steady-state operation may require diverted plasma with H-mode quality confinement.

We report new results from recent particle control and transport experiments in the DIII-D tokamak. We find that dynamic particle balance calculations (particle sources and sinks calculated vs time) yield similar results to a shot-averaged “static” (calculated by pressure rise) particle balance. The dynamic particle balance measurements show very low wall retention in both NBIand ECheated H-modes, compared with large retention during plasma startup. Two oxygen bakes at 1.3 kPa oxygen pressure for 2 hours at 350°C were completed and advanced inductive plasma operation was quickly recovered. No damage to tokamak internal components was observed. The removal of the hydrogenic species in DIII-D by thermo-oxidation compares well with laboratory experiments and we obtained data on thermo-oxidation of fresh C layers in DIII-D. Particle balance in discharges with resonant magnetic perturbation (RMP) ELM suppression show that the wall retention rate and inventory is dependent on pedestal density and divertor conditions. C injection experiments have shown that most of the carbon is deposited at the inner strike point of a SN divertor in L-mode, additional deposition in the private flux zone is present in H-mode. With an unbalanced DN plasma shape, there is more localized C deposition near the injection point in the non-active divertor.

Fusion power gain has been increased by a factor of 3 in DIII-D plasmas through the use of strong discharge shaping and tailoring of the pressure and current density profiles. H-mode plasmas with weak or negative central magnetic shear are found to have neoclassical ion confinement throughout most of the plasma volume. Improved MHD stability is achieved by controlling the plasma pressure profile width. The highest fusion power gain Q (ratio of fusion power to input power) in deuterium plasmas was 0.0015, which extrapolates to an equivalent Q of 0.32 in a deuteriumtritium plasma and is similar to values achieved in tokamaks of larger size and magnetic fields.

Prompt runaway electron bursts, generated by rapidly cooling DIII-D plasmas with argon “killer” pellets, are used to test a recent knock-on avalanche theory describing the growth of multiMeV runaway electron currents during disruptions in tokamaks. Runaway current amplitudes, observed during some but not all DIII-D current quenches, are consistent with growth rates predicted by the theory assuming a pre-current quench runaway electron density of approximately 1015 m-3. Argon “killer” pellet modeling yields runaway densities of between 1015-1016 m-3 in these discharges. Although knock-on avalanching appears to agree rather well with the measurements, relatively small avalanche amplification factors combined with uncertainties in the spatial distribution of pellet mass and cooling rates make it diEcult to unambiguously confirm the proposed theory with existing data. Additional measurements are proposed which should enable us to definitively test the theory.

Fusion power gain has been increased by a factor of 3 in DIII-D plasmas through the use of strong discharge shaping and tailorins of the pressure and current density profiles. H-mode plasmas with weak or negative central magnetic shear are found to have neoclassical ion confinement throughout most of the plasma volume. Improved MHD stability is achieved by controlling the plasma pressure profile width. The highest fusion power gain Q (ratio of fusion power to input power) in deuterium plasmas was 0.0015. which extrapolates to an equivalent Q of 0.32 in a deuteriumtritium plasma and is similar to values achieved in tokamaks of larger size and magnetic fields.

LOCAL ANALYSIS OF CONFINEMENT AND TRANSPORT IN NEUTRAL BEAM HEATED DIII-D DISCHARGES WITH NEGATIVE MAGNETIC SHEAR. High triangularity double-null discharges with weak or negative central magnetic shear and with both an L-mode and an H-mode edge have been produced on DIII-D. The L-mode edge cases are characterized by peaked toroidal rotation, ion temperature, and plasma density profiles with reduced ion transport in the negative shear region. The H-mode edge cases have broader profiles consistent with reduced ion transport, to the neoclassical level, over the entire plasma cross section. The L-mode edge cases have a greater reduction in central ion diffusivity with stronger negative shear while the H-mode edge cases do not exhibit this dependence. Plasma fluctuation measurements show that a dramatic reduction in turbulence accompanies the improved ion confinement. Calculations of sheared EXB flow indicate that this mechanism can overcome the Ili mode growth rate in the region of reduced transport.

We study the electric-field-induced transitions in antiferroelectric liquid crystals in a model that takes into account the intralayer elastic distortion, the nearest-neighbor interlayer interaction, the coupling of the spontaneous polarization with the applied field, the dielectric anisotropy, and the surface anchoring. We find that the field-induced phase sequence has a critical dependence on cell thickness. For moderately thin cells (thickness > 0.1 mum) with moderately strong anchoring (surface coupling similar to 10(-4) J/m(2)), the system, in departing from the initial anticlinic alignment, first undergoes a continuous Freederiksz transition, then a first-order surface boundary-layer transition, and finally a first-order or continuous transition to a complete synclinic ordering. Reducing the cell thickness to less than 0.1 mum will make the Freedericksz transition and even the boundary-layer transition vanish.

Electronic structures of some π-bonded purely organic oligomers have been calculated using a semi-empirical method. These oligomers are the precursors of organic ferromagnets, and for sufficiently high molecular weight are expected to take a helical polymeric form. A statistical-mechanical approach has been used to study the magnetic properties of some of these yet-to-be synthesized helical polymers with possible free radicals. The magnetic susceptibility and the specific heat have been calculated within the framework of the Ising model for a helix with number of spins ranging from 2 to 9 per loop of the helix, and for two sets of values of the inter-loop and intra-loop spin-spin interaction. The electronic structure of certain compounds indicates the possibility of purely organic polymer ferromagnets. Some π-bonded hydrocarbons have their radical/ diradical orbitals lying between a filled valence band and an empty conduction band. These orbitals form a very narrow half-filled band where electrons are expected to be unpaired. The topological arrangement of atoms is important in these materials if the spins of these electrons are to be aligned parallel. We have studied the magnetization of a helical polymer within the framework of the Ising model. The magnetization, the critical temperature and the specific heat have been calculated for helices having various numbers of spins per loop for two values of the ratio of inter-loop to intra-loop interaction. A peak in the zero-field specific heat and saturation in the low-temperature magnetization in the presence of small but non-zero magnetic fields suggest that macroscopic ferromagnetism might occur in a bulk sample of these materials.

Nanocrystalline silver, first introduced as a commercial wound dressing for burns, demonstrates excellent antimicrobial, antifungal, and anti-inflammatory activity. The purpose of this study was to determine if nanocrystalline silver dressings' antimicrobial efficacy is due to the crystallite size (<30 nm) or its polycrystallinity, through the assessment of bactericidal activity of several materials with varying degrees of polycrystallinity.