Finding the elusive E×B staircase in magnetized plasmas.

Turbulence in hot magnetized plasmas is shown to generate permeable localized transport barriers that globally organize into the so-called "ExB staircase" [G. Dif-Pradalier et al., Phys. Rev. E, 82, 025401(R) (2010)]. Its domain of existence and dependence with key plasma parameters is discussed theoretically. Based on these predictions, staircases are observed experimentally in the Tore Supra tokamak by means of high-resolution fast-sweeping X-mode reflectometry. This observation strongly emphasizes the critical role of mesoscale self-organization in plasma turbulence and may have far-reaching consequences for turbulent transport models and their validation.

Improved accuracy and robustness of electron density profiles from JET's X-mode frequency-modulated continuous-wave reflectometers.

JET's frequency-modulated continuous wave (FMCW) reflectometers have been operating well with the current design since 2005, and density profiles have been automatically calculated intershot since then. However, the calculated profiles had long suffered from several shortcomings: poor agreement with other diagnostics, sometimes inappropriately moving radially by several centimeters, elevated levels of radial jitter, and persistent wriggles (strong unphysical oscillations). In this research, several techniques are applied to the reflectometry data analysis, and the shortcomings are significantly improved. Starting with improving the equilibrium reconstruction that estimates the background magnetic field, adding a ripple correction in the reconstructed magnetic field profile, and adding new inner-wall reflection positions estimated through ray-tracing, these changes not only improve the agreement of reconstructed profiles to other diagnostics but also solve density profile wriggles that were present during band transitions. Other smaller but also persistent wriggles were also suppressed by applying a localized correction to the measured beat frequency where persistent oscillations are present. Finally, the burst analysis method, as introduced by Varela et al. [Nucl. Fusion 46 S693 (2006)], has been implemented to extract the beat frequency from stacked spectrograms. Due to the strong suppression of spurious reflections, the radial jitter that sometimes would span several centimeters has been strongly reduced. The stacking of spectrograms has also been shown to be very useful for stacking recurring events, like small gas puff modulations, and extracting transport coefficients that would otherwise be below the noise level.

Experimental electron temperature gradient dependence of heavy impurity transport in fusion devices.

The turbulent impurity (nickel) transport dependence on the normalized electron temperature gradient has been analyzed in sawtooth-free electron cyclotron wave heated Tore Supra plasmas. In the core, our experimental analysis shows that the lower R/L((T)(e)), the lower the nickel diffusion coefficient. The latter decreases until the instability threshold is reached. The experimental threshold is in agreement with the one computed by a gyrokinetic model. Further out, R/L((T)(e)) plays no role in the impurity diffusion. This set of experimental results is consistent with a quasilinear gyrokinetic analysis.

Parametrization of reflectometry fluctuation frequency spectra for systematic study of fusion plasma turbulence.

We describe a way to parameterize power spectra extracted from fixed-frequency reflectometry data, with a view to systematic studies of turbulence properties in tokamak plasmas. Analysis of typical frequency spectra obtained from a new database suggests decomposition in a set of four key components: the direct current component, low-frequency fluctuations, broadband (BB) turbulence, and the noise level. For the decomposition in the identified components, different kinds of functions are tested and their fitting performance is analyzed to determine the optimal spectrum parametrization. In particular, for the BB turbulence, three models are compared qualitatively based on a number of representative spectrum test cases, notably the generalized Gaussian, the Voigt, and the Taylor model. In addition, quantitative performance testing is accomplished using the weighted residual sum of squares and the Bayesian information criterion in a large database including 350 000 spectra obtained in Tore Supra. Next, parametrization by the Taylor model is applied to Ohmically heated plasmas, and a BB energy basin is systematically observed in the core plasma region, which shrinks with decreasing radial position of the q = 1 surface. This basin might be explained by a drop of the density fluctuation level inside the q = 1 surface.

New density profile reconstruction methods in X-mode reflectometry.

The reconstruction method published by Bottollier-Curtet and Ichtchenko in 1987 has been the standard method of density profile reconstruction for X-mode reflectometry ever since, with only minor revision. Envisaging improved accuracy and stability of the reconstruction method, functions more complex than the linear are evaluated here to describe the refractive index shape in each integration step. The stability and accuracy obtained when using parabolic and fixed or adaptative fractional power functions are compared to the previous method and tested against spurious events and phase noise. The developed relation from the plasma parameters to the best integration shapes allows for the optimization of the reconstruction for any profile shape. In addition, the density profiles can be reconstructed using less probing frequencies without accuracy loss, which speed up the reconstruction algorithm and enable real-time monitoring of faster density profile evolution.

Compact ECEI system with in-vessel reflective optics for WEST.

An electron cyclotron emission imaging (ECEI) diagnostic system for WEST (W Environment for Steady state Tokamak) is under development to study the MHD instabilities affected by tungsten impurities. The system will provide 2-D Te fluctuation images (width × height = ∼18 cm × âˆ¼ 34 cm at low field side and ∼13 cm × âˆ¼ 39 cm at high field side) from a poloidal cross section with high spatial (≤1.7 cm) and temporal (≤2 µs) resolutions. While the key concept and electronic structure are similar to that of prior ECEI systems on other tokamak devices such as KSTAR, DIII-D, or ASDEX-U, part of the imaging optics have to be placed inside the vacuum vessel in order to resolve issues on limited installation space and longer beam path to the detector position. The in-vessel optics consisting of two large curvature-radius mirrors are expected to withstand the extreme heating on long-pulse operation scenario (∼1000 s). The out-vessel optical housing is constructed as compact as possible to remove easily from the installation site in case of necessity. Commissioning of the system is scheduled on the second experimental WEST campaign end of 2017.

Design of the reflective optics for Tore Supra ECEI system.

A 2D electron cyclotron emission (ECE) imaging system for Tore Supra is under design for studying the MHD physics of the magnetically confined plasma such as sawteeth, tearing modes, and turbulent fluctuations. Complex beam path due to the tight access in Tore Supra led to the design of reflective optics made of 6 or more large cylindrical∕flat mirrors. The total path length of the ECE beam is about 11 m, including almost 4 m inside the vacuum vessel. The imaging property of the optics has been estimated using the Gaussian beam simulation and ray transfer analysis. The possible setups for the optical alignment of the diagnostic and the operation scenarios with single- or dual-array measurement system are discussed.

Redistribution of suprathermal electrons due to fishbone frequency jumps.

MHD instabilities driven by fast electrons identified as fishbonelike modes have been detected on Tore Supra during lower hybrid current drive discharges. Direct experimental evidence is reported of a novel feature: the regular redistribution of suprathermal electrons toward external tokamak regions which are correlated to periodic mode frequency jumps. Sharp drops of the electron temperature time trace are factually linked to the cyclical deterioration of the fast electron confinement.

Turbulence in the TORE SUPRA tokamak: measurements and validation of nonlinear simulations.

Turbulence measurements in TORE SUPRA tokamak plasmas have been quantitatively compared to predictions by nonlinear gyrokinetic simulations. For the first time, numerical results simultaneously match within experimental uncertainty (a) the magnitude of effective heat diffusivity, (b) rms values of density fluctuations, and (c) wave-number spectra in both the directions perpendicular to the magnetic field. Moreover, the nonlinear simulations help to revise as an instrumental effect the apparent experimental evidence of strong turbulence anisotropy at spatial scales of the order of ion-sound Larmor radius.

Giant oscillations of electron temperature during steady-state operation on Tore Supra.

During fully noninductively driven discharges in the Tore Supra tokamak, large spontaneous oscillations of the core electron temperature (DeltaTe/Te>50%) have been observed for the first time. They occurred during the standard O regime, which is itself characterized by periodic oscillations of much smaller amplitude. The "giant" oscillations appear to involve distinct mechanisms with respect to the O regime and provide a spectacular example of the complex nonlinear interactions between energy confinement, noninductive current sources, and MHD that may occur in a tokamak plasma during steady-state operation.

Comments on "Investing in All the People".

PIP: Professor Summer's article on government spending for education in Pakistan is agreed with. This commentary also suggested that the conference should have included the Ministry of Finance so that there could be multisector agreement that there must be reallocation of public expenditure from the military for future investment in power plants and primary and secondary education systems. The goal would be to eliminate the gender gap in education and to invest in girls' education. Professor Summers argued that inadequate demand needed to be increased with an increased supply of schools. Gender bias was also evident worldwide in missing girls and higher female mortality. Pakistan has the highest sex ratio, which may not reflect a changes in practices among younger mothers. It was argued by Professor Summers that breaking the vicious cycle of high fertility, little or no education, low productivity, and higher mortality among women can be accomplished virtuously by increasing girl's educational levels. The investment in girls will be reaped in the home, marketplace, and in child welfare through changes in household behavior. Educating girls was considered more cost effective than investing in family planning programs. Additional suggestions are provided that improvement in quality of schooling is also important in improving the education of mothers and children and is interactive with mother's education and years of schooling of children. It is likely that if mothers are educated investment returns are greater when quality if enhanced. It would also hold true that investments in health care or in family planning would reap greater returns if mothers are educated. The figures for return on investment are given as over 20% with a doubling of resources over 3.5 years. Returns would be lower if quality is low or jobs are of low quality or if the returns do not appear for another generation. If returns are too low, the question is how this will affect political will. This question remains about why parent's demand for girl's schooling is low when the returns are high. The answer may lie in the unavailability of girl's schools, as was demonstrated in the author's survey of villages with nearly 50% of the villages without a primary school for girls, but with a primary school for boys. "If girl's schools are provided, girls will attend."^ieng

Human capital accumulation in post green revolution rural Pakistan: a progress report.

PIP: There are hugh gender gaps in school enrollments and in cognitive achievements in rural Pakistan. The findings in this study were that the gaps were due to gender differences in school supply. The gender gap in school achievement could have been reduced by half, by eliminating the gender gap in primary school supply, assuming appropriate treatment of preschool ability. Findings also showed that the gender gap in cognitive skills has increased over time, regardless of the more rapid increase in rural schools for girls. Parents now are just as likely to send a girl child to school as a boy child. The gender gap in school supply has narrowed in recent years, except for the age group 10-14 years. School supply can be increased by operating different shifts in boys' schools or with coeducation, which would reduce the need for large capital investments. Cognitive achievement was related to the quantity of rural schooling a child received. There were variations in school quality that were evident and affected girls' cognitive achievement. High quality schools produced more skilled workers, who have an advantage in income potential. Higher levels of educational attainment were related to higher earnings. The estimated return for increasing expenditures on primary schools to insure high quality and increased cognitive achievement was 11%. The rate of return was higher for higher quality schools than primary or middle schools of average quality. Findings were considered tentative and caveats were indicated. Data were obtained from surveys to a panel of over 800 rural households (over 7000 persons) from villages in Attock and Faisalabad districts of the Punjab; respondents were interviewed 4 times a year. The 10th round of the survey was in spring 1989. Background information was provided on gender differences in schooling and the school system. The models yielded 7 equations on gender differences in the determinants of schooling attainment, conditioned on school supply, and in the production of cognitive achievement. Cohorts in ages 20-24 and 30-44 were analyzed separately. Literacy and preschool reasoning ability tests were conducted to assess abilities. Family background, cost of schooling, school characteristics, and school supply were other variables. Background information was given on the issue of quality, and the conceptual framework for returns on quality improvement and quantity increases.^ieng