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The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for future spherical torus (ST) devices and ITER. Plasma durations up to 1.6 s (five current redistribution times) have been achieved at plasma currents of 0.7 MA with non-inductive current fractions above 65% while simultaneously achieving βT and βN values of 17% and 5.7 (%m T MA-1), respectively. A newly available motional Stark effect diagnostic has enabled validation of current-drive sources and improved the understanding of NSTX 'hybrid'-like scenarios. In MHD research, ex-vessel radial field coils have been utilized to infer and correct intrinsic EFs, provide rotation control and actively stabilize the n ≤ 1 resistive wall mode at ITER-relevant low plasma rotation values. In transport and turbulence research, the low aspect ratio and a wide range of achievable β in the NSTX provide unique data for confinement scaling studies, and a new microwave scattering diagnostic is being used to investigate turbulent density fluctuations with wavenumbers extending from ion to electron gyro-scales. In energetic particle research, cyclic neutron rate drops have been associated with the destabilization of multiple large toroidal Alfven eigenmodes (TAEs) analogous to the 'sea-of-TAE' modes predicted for ITER, and three-wave coupling processes have been observed for the first time. In boundary physics research, advanced shape control has enabled studies of the role of magnetic balance in H-mode access and edge localized mode stability. Peak divertor heat flux has been reduced by a factor of 5 using an H-mode-compatible radiative divertor, and lithium conditioning has demonstrated particle pumping and results in improved thermal confinement. Finally, non-solenoidal plasma start-up experiments have achieved plasma currents of 160 kA on closed magnetic flux surfaces utilizing coaxial helicity injection. © 2007 IAEA.

The National Spherical Torus Experiment (NSTX) has explored the effects of shaping on plasma performance as determined by many diverse topics including the stability of global magnetohydrodynamic (MHD) modes (e.g., ideal external kinks and resistive wall modes), edge localized modes (ELMs), bootstrap current drive, divertor flux expansion, and heat transport. Improved shaping capability has been crucial to achieving Βt ∼40%. Precise plasma shape control has been achieved on NSTX using real-time equilibrium reconstruction. NSTX has simultaneously achieved elongation κ∼2.8 and triangularity δ∼0.8. Ideal MHD theory predicts increased stability at high values of shaping factor S≡ q95 Ip (a Bt), which has been observed at large values of the S∼37 [MA (m·T)] on NSTX. The behavior of ELMs is observed to depend on plasma shape. A description of the ELM regimes attained as shape is varied will be presented. Increased shaping is predicted to increase the bootstrap fraction at fixed Ip. The achievement of strong shaping has enabled operation with 1 s pulses with Ip =1 MA, and for 1.6 s for Ip =700 kA. Analysis of the noninductive current fraction as well as empirical analysis of the achievable plasma pulse length as elongation is varied will be presented. Data are presented showing a reduction in peak divertor heat load due to increasing in flux expansion. © 2006 American Institute of Physics.

In order to reduce recirculating power fraction to acceptable levels, the spherical torus concept relies on the simultaneous achievement of high toroidal β and high bootstrap fraction in steady state. In the last year, as a result of plasma control system improvements, the achievable plasma elongation on NSTX has been raised from κ ∼ 2.1 to κ ∼ 2.6 - approximately a 25% increase. This increase in elongation has led to a substantial increase in the toroidal β for long pulse discharges. The increase in β is associated with an increase in plasma current at nearly fixed poloidal β, which enables higher βt with nearly constant bootstrap fraction. As a result, for the first time in a spherical torus, a discharge with a plasma current of 1 MA has been sustained for 1 s (0.8 s current flat-top). Data are presented from NSTX correlating the increase in performance with increased plasma shaping capability. In addition to improved shaping, H-modes induced during the current ramp phase of the plasma discharge have been used to reduce flux consumption and to delay the onset of MHD instabilities. Based on these results, a modelled integrated scenario, which has 100% non-inductive current drive with very high toroidal β, will also be discussed. The NSTX poloidal field coils are currently being modified to produce the plasma shape which is required for this scenario, which requires high triangularity (δ ∼ 0.8) at elevated elongation (κ ∼ 2.5). The other main requirement of steady state on NSTX is the ability to drive a fraction of the total plasma current with RF waves. The results of high harmonic fast wave heating and current drive studies as well as electron Bernstein wave emission studies will be presented. © 2006 IAEA, Vienna.

Research on the spherical torus (or spherical tokamak) (ST) is being pursued to explore the scientific benefits of modifying the field line structue fro that in more moderate aspect ratio devices. The ST experiments are being conducted in various US research facilities. The area of power and particle handling is expected to be challenging because of the higher power density expected in the ST relative to that in conventional aspect-ratio tokamaks.

A major research goal of the national spherical torus experiment is establishing long-pulse, high beta, high confinement operation and its physics basis. This research has been enabled by facility capabilities developed during 2001 and 2002, including neutral beam (up to 7 MW) and high harmonic fast wave (HHFW) heating (up to 6 MW), toroidal fields up to 6 kG, plasma currents up to 1.5 MA, flexible shape control, and wall preparation techniques. These capabilities have enabled the generation of plasmas with βT ≡ /(BT02/2μ0) of up to 35%. Normalized beta values often exceed the no-wall limit, and studies suggest that passive wall mode stabilization enables this for H mode plasmas with broad pressure profiles. The viability of long, high bootstrap current fraction operations has been established for ELMing H mode plasmas with toroidal beta values in excess of 15% and sustained for several current relaxation times. Improvements in wall conditioning and fuelling are likely contributing to a reduction in H mode power thresholds. Electron thermal conduction is the dominant thermal loss channel is auxiliary heated plasmas examined thus far. HHFW effectively heats electrons, and its acceleration of fast beam ions has been observed. Evidence for HHFW current drive is obtained by comparison of the loop voltage evolution in plasmas with matched density and temperature profiles but varying phases of launched HHFW waves. Studies of emissions from electron Bernstein waves indicate a density scale length dependence of their transmission across the upper hybrid resonance near the plasma edge that is consistent with theoretical predictions. A peak heat flux to the divertor targets of 10 MW m-2 has been measured in the H mode, with large asymmetries being observed in the power deposition between the inner and outer strike points. Non-inductive plasma startup studies have focused on coaxial helicity injection. With this technique, toroidal currents up to 400 kA have been driven, and studies to assess flux closure and coupling to other current drive techniques have begun.

The National Spherical Torus Experiment (NSTX) at Princeton University, Princeton, NJ, is designed to assess the potential of the low-aspect-ratio spherical torus concept for magnetic plasma confinement. The plasma has been heated by up to 7 MW of neutral beam injection (NBI) at an injection energy of 100 keV and up to 6 MW of high harmonic fast wave (HHFW) at 30 MHz. NSTX has achieved [[beta].sub.T] of 32%. A variety of MHD phenomena have been observed to limit [beta]. NSTX has now begun addressing [T.sub.E] scaling, [beta] limits, and current drive issues. During the NBI heating experiments, a broad [T.sub.i] profile with [T.sub.i] up to 2 keV, [T.sub.i] > [T.sub.e] and a large toroidal rotation were observed. Transport analysis suggests that the impurity ions have diffusivities approaching neoclassical. For L-Mode plasmas, [T.sub.E] is up to two times the ITER97L H-Mode scaling and exceeds the ITER98pby2 H-Mode scaling in some cases. Transitions to H-Mode have been observed which result in an approximate doubling of [T.sub.E] after the transition in some conditions. During HHFW heating, [T.sub.e] > [T.sub.i] and [T.sub.e] up to 3.5 keV were observed. Current drive has been studied using both coaxial helicity injection with up to 390 kA of toroidal current and HHFW. HHFW has produced H-modes with significant bootstrap current fraction at low [I.sub.p], high q, and high [[beta].sub.p]. Index Terms--Fusion reactors, plasma confinement, tokamaks.

In the present paper, abnormal feather development associated with an in ovo avian leukosis virus (ALV) subgroup J infection in specific pathogen free broilers is reported. A description of gross lesions is given, together with the results of light microscopic, immunohistochemical and ultrastructural studies to further elucidate the characteristics of the feather pathology and to assess the presence of ALV subtype J in broiler feathers. The feather lesions found, which were mainly restricted to primary and secondary remiges, were thinness and increased transparency of the calamus and sparseness of the vane. In a few cases, feather growth retardation was present, while the vane remained ensheathed. Light microscopy did not reveal abnormalities, although immunohistochemically prominent anti-p27 staining was found in the central area of the feather pulp between cells forming the barbular epithelium. Transmission electron microscopy showed the presence of retroviral particles in various structures of the feather (epidermal collar and intermediate layer of feather epidermis), most virus being present in the same area that stained most prominently by immunohistochemistry and where apparently intra-epithelial gaps were seen. ALV was isolated from the upper two-thirds of primary remiges of almost all inoculated birds and 40% of contact birds. Polymerase chain reaction of cell cultures showed that the virus isolates belonged to subgroup J. This study shows that subtype J virus can be massively present in feather tissue of infected birds, which could have consequences for its transmission and diagnosis. [ABSTRACT FROM AUTHOR]

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010. [ABSTRACT FROM PUBLISHER]

Hard X-ray free-electron lasers (XFELs) generate intense coherent X-ray beams by passing electrons through undulators, i.e. very long periodic magnet structures, which extend over hundreds of meters. The SASE1 and SASE2 undulator systems of the European XFEL consist of 35 segments with variable-gap planar undulators which are initially tuned to precise on-axis magnetic field strengths in a magnetic measurement laboratory to keep an important quality parameter - the K-value variation from segment to segment - below a certain limit (3 × 10 -4 for 12 keV photon energy). After tunnel installation only photon-based methods can determine the K-values of undulator segments with a similar accuracy. The synchrotron radiation from a single or a few segments can be spectrally filtered by a dedicated crystal monochromator (K-monochromator) and recorded with a photodiode or with an imager that provides 2D information, tuned for high sensitivity to detect low photon densities from distant single undulator segments. This instrumentation is applied for electron orbit analysis and optimization, and adjustment of individual undulators in terms of their central magnetic axis with respect to the electron beam. Single undulator segments were analysed by scanning the monochromator crystal angle and detecting the steepest slope of a photodiode signal. Alternatively, in the imaging method, an imager recorded the radiation cone of electrons passing through the undulator segment. From the spatial distribution of the radiation, the K-parameter was determined with a sufficiently high relative accuracy.