1,721,303 research outputs found
Linearized models for a new magnetic control in MAST
No full textThe aim of this work is to provide reliable linearized models for the design and assessment of a new magnetic control system for MAST (Mega Ampère Spherical Tokamak) using rtEFIT, which can easily be exported to MAST Upgrade. Linearized models for magnetic control have been obtained using the 2D axisymmetric finite element code CREATE L. MAST linearized models include equivalent 2D axisymmetric schematization of poloidal field (PF) coils, vacuum vessel, and other conducting structures. A plasmaless and a double null configuration have been chosen as benchmark cases for the comparison with experimental data and EFIT reconstructions. Good agreement has been found with the EFIT flux map and the experimental signals coming from magnetic probes with only few mismatches probably due to broken sensors. A suite of procedures (equipped with a user friendly interface to be run even remotely) to provide linearized models for magnetic control is now available on the MAST linux machines. A new current driven model has been used to obtain a state space model having the PF coil currents as inputs. Dynamic simulations of experimental data have been carried out using linearized models, including modelling of the effects of the passive structures, showing a fair agreement. The modelling activity has been useful also to reproduce accurately the interaction between plasma current and radial position control loops. © 2013 Euratom-ENEA Association sulla Fusione
Alternative equilibrium reconstruction code for FTU plasma control
No full text[No abstract available
An overview of the software architecture of the plasma position, current and density realtime controller of the FTU
No full textExperimental fusion devices requires flexible control systems with a modern architecture, which allows the controller to be distributed and modular. The aforementioned requirements are all fulfilled by MARTe, a multi-platform framework for the development of low-latency hard-real-time control system already used with success in many European machine, it was decided to adopt it as the basis of the new FTU Plasma Position Current Density Control (PPCDC) system and the other coupled realtime systems. The main rationale to revamp the FTU control system was to use new technologies and to easily test different control solutions. MARTe has been proved effective from both the points of view, being platform independent, and having a modular architecture which completely separate the control algorithms from the rest of the infrastructure. We report on the new controller deployed at FTU. In particular, after a brief introduction on the machine, we illustrate the structure of the feedback system, together with a detailed analysis and appropriate experimental examples, of the various GAMs (modules) which make up the controller. ᄅ 2014 EURATOM-ENEA Association
Divertor load footprint of ELMs in pellet triggering and pacing experiments at JET
No full textAn investigation of pellet pacing and triggering of Edge Localized Modes (ELMs) was carried out in the frame of ELM mitigation studies aimed at reducing their damaging effects on the plasma-facing components (PFCs). The divertor power load footprint of triggered ELMs was compared with gas puffing controlled ELMs. Small pellets, corresponding to a few per cent of the target plasma particle inventory, were used to minimize the fueling effect and the total particle throughput. There is no evidence that pellets can reduce the divertor power load with respect to gas fueling when operating at the same ELM frequency. The line average density and the energy confinement time remained constant when the gas was progressively substituted by pellets. The launch from the Vertical High Field Side (VHFS) confirmed to be more efficient in ELM triggering than from the Low Field Side (LFS) while the power load footprint remained the same both in time evolution and in spatial distribution when changing the injection geometry. © 2015 Elsevier B.V
A new approach to the solution of the vacuum magnetic problem in fusion machines
No full textThe magnetic vacuum topology reconstruction using magnetic measurements is essential in controlling and understanding plasmas produced in magnetic confinement fusion devices. In a wide range of cases, the instruments used to approach the problem have been designed for a specific machine and to solve a specific plasma model. Recently, a new approach has been used for developing new magnetic software called FELIX. The adopted solution in the design allows the use of the software not only at JET but also at other machines. In order to reduce the analysis and debugging time the software has been designed with modularity and platform independence in mind. This results in a large portability and in particular it allows using the same code both offline and in real-time. One of the main aspects of the tool is its capability to solve different plasma models of current distribution. Thanks to this feature, in order to improve the plasma magnetic reconstruction in real-time, a set of different models has been run using FELIX. FELIX is presently running at JET in different real-time analysis and control systems that need vacuum magnetic topology
Identification of Vertical Instabilities in the JET Tokamak
No full textThis paper deals with the electromagnetic aspects related to a series of experiments aimed at the identification and control of vertical instabilities in the JET Tokamak. The first part of the work is devoted to model the transient magnetic fields produced by the poloidal field circuits and the plasma edge localized modes (ELMs). The second part describes the approach used to design an ELM independent plasma speed estimator. The design of the estimator had to be developed with the constraint of using the present controller parameters, so as to minimize the impact on JET operation
Initial low recycling improving confinement and current drive in advanced tokamak (at) and hybrid scenarios
No full textTo improve stability and confinement in fusion plasmas via sufficient control of the plasma current profile represents a major objective for the progress of thermonuclear fusion research based on the tokamak concept. The lower hybrid current drive (LHCD) would provide a solution, by removing the problematic extrapolation of LHCD to high plasma densities, as demonstrated on FTU. However, since LHCD is not approved yet in ITER and is difficult to foresee its presence in DEMO, the issue remains on how producing a high bootstrap fraction (/bs > 50%) in the unfavorable condition of relatively low q95 (< 5). We focus here on the proper (initial) condition of a low particle recycling from the vessel wall, which should be performed before starting the main heating phase, as useful for enhancing the bootstrap current density at large radii of the plasma column. Experiments in ITER-like wall, relevant to hybrid scenario with (795≈ 4.5 and performed with an initial compression and expansion of plasma volume with the aim of changing the g-profile, exhibited a lower initial recycling, a higher electron temperature of periphery, and a higher normalised β (βN) in H-mode. A similar effect of the initial level of recycling was found in statistics of plasma discharges performed in C-wall, relevant for AT scenario with q95≈ 5. Modelling of current density profile evolution shows that a larger bootstrap current occurs at large radii in case of lower initial recycling, effect of larger electron temperature produced at large radii. Analysis of microinstability in L-mode phase shows that ETG modes have smaller linear growth rate in case with lower recycling. From stability analysis performed during the high (3N phase, a bigger margin of stability minimum shear occurs near the plasma periphery, thanks to current drive improved by the proper initial edge condition
- …
