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Loarte A.,Culham Center for Fusion Energy | Loarte A.,ITER Organization | Leyland M.J.,University of York | Mier J.A.,University of Cantabria | And 7 more authors.
Nuclear Fusion | Year: 2013

The build-up of plasma parameters following the H-mode transition in JET has been analysed in view of its consequences for the alpha power evolution in the access to burning plasma conditions in ITER. JET experiments show that the build-up of plasma temperature both at the plasma core and the plasma edge occurs in timescales comparable to the energy confinement time. In contrast, the evolution of the edge and core densities differs strongly depending on the level of plasma current in the discharge and of the associated NBI penetration. For higher plasma current H-mode discharges (Ip > 2.0-2.5 MA, depending on plasma shape), with naturally higher plasma densities for which NBI penetration is poorer, the core density evolves in much longer timescales than the edge density leading to the formation of rather hollow density profiles. These hollow density profiles persist for timescales of several energy confinement times until they are usually terminated by a sawtooth. Modelling of the JET experiments with JETTO shows that the density build-up following the H-mode transition can be described with a purely diffusive model, despite the low collisionalities of high current H-mode plasmas at JET. The consequences of these JET experimental/modelling findings for the access to burning plasma conditions in the ITER QDT = 10 scenario are presented. © 2013 IAEA, Vienna.

Oliva E.,ENSTA ParisTech | Fajardo M.,Institute Plasmas e Fusao Nuclear | Li L.,ENSTA ParisTech | Sebban S.,ENSTA ParisTech | And 2 more authors.
Optics Letters | Year: 2012

To date, plasma-based soft x-ray lasers have demonstrated experimentally 1 μJ, 1 ps (1 MW) pulses. This Letter reports extensive study using time-dependant Maxwell-Bloch code of seeding millimeter scale plasmas that store more than 100 mJ in population inversion. Direct seeding of these plasmas has to overcome very strong amplified spontaneous emission (ASE) as well as prevent wake-field amplification. Below 100 nJ injected energy, seed produces pulses with picosecond duration. To overcome this limitation, a new scheme has been studied, taking advantage of a plasma preamplifier that dramatically increases the seed energy prior to entering the main plasma amplifier leading to ASE and wake-free, fully coherent 21.6 μJ, 80 fs pulses (0.27 GW). © 2012 Optical Society of America.

Rodriguez-Pascual M.,CIEMAT | Scott B.D.,Max Planck Institute for Plasma Physics (Garching) | Ribeiro T.T.,Max Planck Institute for Plasma Physics (Garching) | Ribeiro T.T.,Institute Plasmas e Fusao Nuclear | And 3 more authors.
IEEE Transactions on Plasma Science | Year: 2010

The study of core turbulence represents a key line of research in fusion plasmas. By adding collisions and electromagnetic induction to the parallel dynamics of the standard six-moment toroidal model, it is possible to study the gyrofluid electromagnetic phenomena in the context of edge turbulence with the GEM code. Currently, the code describes the fluctuation free-energy conservation in a gyrofluid model by means of the polarization equation which relates the ExB flow and eddy energy to the combinations of the potential, the density, and the perpendicular temperature. To do so, supercomputers have been used only to date. In this paper, we demonstrate its feasibility as a cluster application on a production environment based on any kind of distributed memory, enhancing in this way its scope. The scalability (which grows linearly with a correlation factor of 0.99978) and the correctness of our solution with respect to the previous GEM version have been evaluated in a local cluster of 88 nodes. The fault tolerance and the Grid suitability have been demonstrated by executing our application in the EUrope Fusion for ITER Applications infrastructure by adapting the code to this paradigm and by improving its parallel Grid performance. It can be employed on its own or belonging to workflows in order to perform a wider more complex analysis of fusion reactors. © 2010 IEEE.

Mendes R.V.,University of Lisbon | Mendes R.V.,Institute Plasmas e Fusao Nuclear
Physica Scripta | Year: 2015

Non-commutative tomography is a technique originally developed and extensively used by Professors M A Man'ko and V I Man'ko in quantum mechanics. Because signal processing deals with operators that, in general, do not commute with time, the same technique has a natural extension to this domain. Here, a review is presented of the theory and some applications of non-commutative tomography for time series as well as some new results on signal processing on graphs. © 2015 The Royal Swedish Academy of Sciences.

Bertolami O.,University of Porto | Francisco F.,University of Lisbon | Gil P.J.S.,University of Lisbon | PAramos J.,University of Lisbon | PAramos J.,Institute Plasmas e Fusao Nuclear
International Journal of Modern Physics D | Year: 2012

We propose the concept of a space mission to probe the so called flyby anomaly, an unexpected velocity change experienced by some deep-space probes using earth gravity assists. The key feature of this proposal is the use of GNSS systems to obtain an increased accuracy in the tracking of the approaching spacecraft, mainly near the perigee. Two low-cost options are also discussed to further test this anomaly: an add-on to an existing spacecraft and a dedicated mission. © 2012 World Scientific Publishing Company.

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