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[en] The IAEA Technical Committee Meeting on Research Using Small Tokamaks, held in Arlington, Virginia, 27-29 September, 1990, is summarized. This meeting provided a forum for countries with small or developing tokamak programmes to present their results and exchange ideas. A list of the small tokamaks discussed at the meeting is included. 1 tab
[en] This report presents the Fifth IAEA Technical Committee Meeting on Large Tokamak Experiments held at Princeton, January 1984. A brief presentation of the parameters of the six large tokamaks, out of which two (TFTR and JET) are conditioning Ohmic heating experiments, is first given. Then details are given concerning the status of specific hardware, such as the vacuum system, on-line computer systems, RF heating, neutral beams, power systems and coils, tritium and activation. The final sections deal with scientific developments and operating plans of existing facilities, information anticipated from the research programmes, and proposals for next-generation tokamaks
[en] Experiments on the Pegasus ST are advancing the physics and technology basis of local helicity injection (LHI). LHI injects helicity with relatively intense electron current sources in the plasma edge. It creates high toroidal current, toroidally-averaged tokamak-like plasmas that have been efficiently transitioned to Ohmically driven tokamak plasmas. Tradeoffs between physics and engineering goals are tested with LHI systems on the low-field-side and the high-field-side of Pegasus, producing plasmas predominantly driven by non-solenoidal induction and DC helicity drive, respectively. An extensive LHI source development campaign comparing active arc sources, passive and gas-effused electrode sources lead to the selection of active arc sources for present and next-step LHI deployments. LHI plasmas with net toroidal current MA, eV, and m−3 are attained to date. A predictive 0D power-balance model describes experimental and partitions the active current drive sources. High-frequency MHD activity is found to be present during LHI current drive, in addition to modes previously found in NIMROD simulation and experiment. A new regime of reduced MHD activity was discovered where activity is suppressed, LHI CD efficiency improves, and long-pulse plasmas are sustained with . (paper)
[en] Understanding the many aspects of tokamak physics requires the development of quite sophisticated models. Moreover, in the operation of the devices, prediction of the future evolution of discharges can be of crucial importance, particularly in the case of the prediction of disruptions, which can cause serious damage to various parts of the machine. The determination of the limits of predictability is therefore an important issue for modelling, classifying and forecasting. In all these cases, once a certain level of performance has been reached, the question typically arises as to whether all the information available in the data has been exploited, or whether there are still margins for improvement of the tools being developed. In this paper, a theoretical information approach is proposed to address this issue. The excellent properties of the developed indicator, called the prediction factor (PF), have been proved with the help of a series of numerical tests. Its application to some typical behaviour relating to macroscopic instabilities in tokamaks has shown very positive results. The prediction factor has also been used to assess the performance of disruption predictors running in real time in the JET system, including the one systematically deployed in the feedback loop for mitigation purposes. The main conclusion is that the most advanced predictors basically exploit all the information contained in the locked mode signal on which they are based. Therefore, qualitative improvements in disruption prediction performance in JET would need the processing of additional signals, probably profiles. (paper)
[en] A low flow, δf gyrokinetic formulation to obtain the intrinsic rotation profiles is presented. The momentum conservation equation in the low-flow ordering contains new terms, neglected in previous first-principles formulations, that may explain the intrinsic rotation observed in tokamaks in the absence of external sources of momentum. The intrinsic rotation profile depends on the density and temperature profiles and on the up-down asymmetry.
[en] Localized current injection near the outboard midplane is used to form 0.1 MA plasma discharges with no induction supplied from a central solenoid in the ultra-low aspect ratio Pegasus Toroidal Experiment. The discharges are initiated by driving open-field-line currents that perturb the vacuum magnetic field such that the magnetic topology transitions to a tokamak-like configuration. The plasma is subsequently driven via helicity injection from the edge current sources and poloidal field induction. Intermittent n = 1 MHD activity is observed during periods of strong edge current drive and each event leads to a rapid inward expansion of the plasma volume and a drop in the plasma inductance. The plasmas are sufficiently turbulent such that the equilibrium approaches the lowest energy state described by Taylor relaxation theory. In agreement with that theory, the maximum Ip scales with (ITFIinj/w)1/2, where ITF is the toroidal field rod current, Iinj is the injected edge current and w is the radial width of the average poloidal magnetic flux in the driven open flux region.