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This paper addresses one aspect of the problem of the suppression of tearing mode magnetic islands by electron cyclotron current drive (ECCD) injection, formulating the problem as the converse of a forced reconnection problem. New physical conditions are discussed which should be considered in the technical approach towards a robust control strategy. Limits on the ECCD deposition are determined to avoid driving the system into regimes where secondary instabilities develop. Numerical simulations confirming the theory are also presented.
This paper reviews key aspects of the problem of magnetic islands control by electron cyclotron current drive in fusion devices. On the basis of the ordering of the basic spatial and time scales of the magnetic reconnection physics, we present the established results, highlighting some of the open issues posed by the small-scale structures that typically accompany the nonlinear evolution of the magnetic islands and constrain the effect of the control action.
A discharge-produced-plasma (DPP) source emitting in the extreme ultraviolet (EUV) spectral region is running at the ENEA Frascati Research Centre. The plasma is generated in low-pressure xenon gas and efficiently emits 100-ns duration radiation pulses in the 10–20-nm wavelength range, with an energy of
at a 10-Hz repetition rate. The complex discharge evolution is constantly examined and controlled with electrical measurements, while a ns-gated CCD camera allowed observation of the discharge development in the visible, detection of time-resolved plasma-column pinching, and optimization of the pre-ionization timing. Accurately calibrated Zr-filtered PIN diodes are used to monitor the temporal behaviour and energy emission of the EUV pulses, while the calibration of a dosimetric film allows quantitative imaging of the emitted radiation. This comprehensive plasma diagnostics has demonstrated its effectiveness in suitably adjusting the source configuration for several applications, such as exposures of photonic materials and innovative photoresists.
The formation and evolution of Solar System small bodies, in particular those in near-Earth orbits, is a complex problem which solution strongly depends on a better knowledge of their physical properties. To contribute to the international efforts in this direction the IMPACTON project (www.on.br/IMPACTON) set up a dedicated facility denominated Observatório Astronômico do Sertão de Itaparica (OASI). Using the 1-m telescope several dozens of NEAs were observed between March 2012 and October 2014. Here we will present the results obtained for 8 objects. Relative magnitudes were used to obtain lightcurves and derive rotational periods. Applying the inversion method developed by Kaasalainen and Torppa (2001) and Kaasalainen et al. (2001), along with lightcurves from literature, allowed to refine the rotational period of these asteroids as well as to derive their pole direction and shape. The obtained results confirm a lack of poles toward the ecliptic and with a majority of retrograde rotators. A more representative sample, however, is needed in order to drive robust conclusions.
A total of 701 comets received names between July 2005 and June 2008. Comets observed only from the SOHO and STEREO missions, as well as further comets recognized from the long-defunct SOLWIND satellite, accounted for 520 of these names.
The past triennium has continued to see a huge influx of astrometric positions of small solar system bodies provided by near-Earth object (NEO) surveys. As a result, the size of the orbital databases of all populations of small solar system bodies continues to increase dramatically, and this in turn allows finer and finer analyses of the types of motion in various regions of the orbital elements space.
As for comets 619 comets received names from July 2002 to June 2005. Of this naming 76 percent are SOHO comets and 11 percent include the name of the LINEAR project. A revision of the guidelines for naming comets has been completed in March 2003. The assistance of the director of CBAT, Daniel W. E. Green, in redrafting these guidelines was much appreciated by the committee.
The spatial shaping of light beams is the process of redistributing the
irradiance of a light beam. A correct beam shaping is essential to optimize
a large number of laser-material processing applications and laser-material
interaction studies. In this paper, after introducing the basic equations of
the classical beam integration method to reshape and homogenize laser beams,
we detail the design elements, the experimental performance and the main
parameters of a novel transfocal homogenizer that is able to homogenize and
reshape any light beam. Then we discuss the reliability of existing
international standard parameters to evaluate the “goodness” of nearly
flat-top shaped laser beams. Finally, we present examples of successful
applications of this new homogenizer technology to ultraviolet irradiation
New easy spectrally tunable backlighting schemes based on a
spherically bent crystal are considered. Contrary to traditional
backlighting scheme, in which the investigated objects should be placed
between the backlighter and the crystal, for the considered schemes an
object is placed downstream of the crystal, before the tangential or
after the sagittal focus and an image of the object is recorded at the
distance from the object corresponding to the needed magnification. The
magnification is defined by the ratio of the distances from the
sagittal focus to the detector and from the object to the sagittal
focus. A ray-tracing modeling and experimental images of test meshes,
obtained at incidence angles of the backlighter radiation of 10°
and 22°, are presented. It is demonstrated that a simple linear
transformation of the obtained astigmatic images allows reconstructing
them as a stigmatic with an accuracy of 5–15%. For the spectral
range around 9 Å a spatial resolution about 10 μm in a field
of view of some square millimeters is achieved experimentally and
confirmed by ray-tracing simulations.
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