1. magnetic confinement - ENEA - Fusione

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26 1. MAGNETIC CONFINEMENT 1.1 Tokamak Physics t=46.5 s). No change in plasma-edge activity is observed in concomitance with the ITB collapse. 1 The effect of LHCD on magnetic shear might have helped to sustain the ITB in shot #53429, as 0 suggested by the modelling analysis performed by the JETTO code [1.30] and LH ray 2- D Fokker Planck ray tracing. As -1 a result [1.31], the power is fully deposited off-axis within the layer ρ≈0.4-0.7, with a maximum at ρ≈0.5 (ρ is the square root of the normalised toroidal flux). The ITB is located in this layer. The calculated fraction of LH 0.3 0.4 0.5 ρ 0.6 0.7 0.8 driven current is I LHCD /I P ≈0.25, while the noninductive current fraction is (I LHCD +I boot +I NBI )/I P ≈0.65. 0.5 The q-profile of discharge t = 47s #53429 simulated by the t = 46s JETTO code shows a reversed 0 shape during the main heating phase. Figure 1.19 reports the simulated -0.5 magnetic shear profiles at 0.3 0.4 different times during the ρ main heating phase. After the LH power is switched on, the 0.5 0.6 s=0 layer of the magnetic shear profile moves outward and persists in the region ρ>0.3. As anomalous transport is dominant in this region, the low/negative magnetic shear could inhibit the growth of turbulent modes that cause the ITB collapse. No change in the q profile is expected at the time of the ITB collapse in the experiment. However, the collapse might be related to edge physics, as it accompanies an increase in Dα emission. Magnetic shear s Magnetic shear s For shot #53429, with LH power coupled during the main heating phase, modelling suggests that the collapse can be produced by an inward movement of the s=0 layer [(ρ
1. MAGNETIC CONFINEMENT 27 1.2.1 FTU machine 1.2 FTU Facilities Summary of machine operation The FTU machine operated throughout 2001, with only the one summer shutdown. No major problems arose during the experimental campaigns, except for a vacuum leak during startup in February and, consequently, the loss of two experimental weeks. In fact, during the experimental phase, with full available power, strong influxes on the manganese caused systematic plasma disruptions. This behaviour originated from the heat load on the stainless steel structure of the MHD rings that acted as a limiter inside the vacuum vessel, so the rings were removed during the summer shutdown. With the new boronisation system, the scientific objectives of reducing Z eff and radiative losses, especially at low density, were reached. The first boronisation of the vacuum vessel in October 2001 was performed with the machine at room temperature. Afterwards, it was done with the machine cooled down to liquid nitrogen temperature and baking the vessel so that only one experimental day was lost instead of a week. The remote handling tools for vacuum-vessel inspections are continuously updated. It is now possible to visually examine the vessel through only one port. The new remote arm covers half the torus in one direction and the other half in the opposite direction. The images are digitalised and stored in a computer connected to Internet and available to all users. The scientific exploitation of FTU data is strictly related to data-access tools, so particular attention was devoted to this aspect. In addition to the AFS and the MDSplus servers, a new data layer that is compatible with the standard CORBA was developed to allow users to access data from their own PC by running a local Matlab or IDL code. This effort can also be considered as part of the general issue of remote participation, which has been greatly emphasised since the establishment of the multilateral European Fusion Development Agreement (EFDA) on which the European fusion research program is based. Again in this framework, the assessment of video conferencing tools, namely the Virtual Rooms Videoconferencing System (VRVS), was completed. Two permanent conference rooms and one movable station, equipped with PCs, were set up for Local Presentation, VRVS mbone, VNC sharing presentation transmission, unidirectional WebCast and Yahoo chatting. A number of personal VRVS-desktop set-ups are also available, but have not yet been used. Remote meetings were organised between ENEA Frascati, CNR Milano, CNR Padova and EFDA JET. Fig. 1.21 - Sources of downtime. During 2001, 1909 shots were completed successfully out of a total of 2117 performed in 91 experimental days. The average number of successful daily pulses was 20.95. Table 1.II gives the main parameters for evaluating the efficiency of the experimental sessions. Figure 1.21 reports the source of downtime in 2001. It is worth noting that the time required to analyse the discharges is still the main source of downtime. During the experimental Analysis 27% Diagnostic Systems 8% Others 9% Machine 9% Control System 17% Power Supplies 15% Radiofrequency 15% campaigns the tokamak power supplies and the control and data acquisition system operated at a very high level of availability and reliability. The percentage of time lost because of controlsystem problems was reduced to 17%.
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150 ABBREVIATIONS AND ACRONYMS EC E
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152 ABBREVIATIONS AND ACRONYMS LHC
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154 ABBREVIATIONS AND ACRONYMS WDS
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