901 research outputs found
Effect of kinetic resonances on the stability of Resistive Wall Mode in Reversed Field Pinch
The kinetic effects, due to the mode resonance with thermal particle drift
motions in the reversed field pinch (RFP) plasmas, are numerically investigated
for the stability of the resistive wall mode, using a non-perturbative
MHD-kinetic hybrid formulation. The kinetic effects are generally found too
weak to substantially change the mode growth rate, or the stability margin,
re-enforcing the fact that the ideal MHD model is rather adequate for
describing the RWM physics in RFP experiments.Comment: Submitted to: Plasma Phys. Control. Fusio
Electromagnetic filaments and edge modifications induced by electrode biasing in the RFX-mod tokamak
An active feedback recovery technique from disruption events induced by m=2 n=1 tearing modes in ohmically heated tokamak plasmas
We present experimental results of magnetic feedback control on the m=2, n=1
tearing mode in RFX-mod operated as a circular ohmically heated tokamak. The
feedback suppression of the non-resonant m=2, n=1 Resistive Wall Mode (RWM) in
q(a)<2 plasmas is a well-established result of RFX-mod. The control of the
tearing counterpart, which develops in q(a)>2 equilibrium, is instead a more
difficult issue. In fact, the disruption induced by a growing amplitude m=2,
n=1 tearing mode can be prevented by feedback only when the resonant surface
q=2 is close to the plasma edge, namely 2<q(a)<2.5, and the electron density
does not exceed approximately half of the Greenwald limit. A combined technique
of tearing mode and q(a) control has been therefore developed to recover the
discharge from the most critical conditions: the potentially disruptive tearing
mode is converted into the relatively benign RWM by suddenly decreasing q(a)
below 2. The experiments demonstrate the concept with 100% of successful cases.
The q(a) control has been performed through the plasma current, given the
capability of the toroidal loop-voltage power supply of RFX-mod. We also
propose a path for controlling q(a) by acting on the plasma shape, which could
be applied to medium size elongated tokamaks
Statistical features of edge turbulence in RFX-mod from Gas Puffing Imaging
Plasma density fluctuations in the edge plasma of the RFX-mod device are
measured through the Gas Puffing Imaging Diagnostics. Statistical features of
the signal are quantified in terms of the Probability Distribution Function
(PDF), and computed for several kinds of discharges. The PDFs from discharges
without particular control methods are found to be adequately described by a
Gamma function, consistently with the recent results by Graves et al [J.P.
Graves, et al, Plasma Phys. Control. Fusion 47, L1 (2005)]. On the other hand,
pulses with external methods for plasma control feature modified PDFs. A first
empirical analysis suggests that they may be interpolated through a linear
combination of simple functions. An inspection of the literature shows that
this kind of PDFs is common to other devices as well, and has been suggested to
be due to the simultaneous presence of different mechanisms driving
respectively coherent bursts and gaussian background turbulence. An attempt is
made to relate differences in the PDFs to plasma conditions such as the local
shift of the plasma column. A simple phenomenological model to interpret the
nature of the PDF and assign a meaning to its parameters is also developed.Comment: 27 pages. Published in PPC
The Italian open data meteorological portal: MISTRAL
At the national level, in Italy, observational and forecast data are collected by various public bodies and are often kept in various small, heterogeneous and non-interoperable repositories, released under different licenses, thus limiting the usability for external users. In this context, MISTRAL (the Meteo Italian SupercompuTing PoRtAL) was launched as the first Italian meteorological open data portal, with the aim of promoting the reuse of meteorological data sets available at national level coverage. The MISTRAL portal provides (and archives) meteorological data from various observation networks, both public and private, and forecast data that are generated and post-processed within the Consortium for Small-scale Modeling-Limited Area Model Italia (COSMO-LAMI) agreement using high performance computing (HPC) facilities. Also incorporated is the Italy Flash Flood use case, implemented with the collaboration of European Centre for Medium-Range Weather Forecasts (ECMWF), which exploits cutting edge advances in HPC-based post-processing of ensemble precipitation forecasts, for different model resolutions, and applies those to deliver novel blended-resolution forecasts specifically for Italy. Finally, in addition to providing architectures for the acquisition and display of observational data, MISTRAL also delivers an interactive system for visualizing forecast data of different resolutions as superimposed multi-layer maps
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