Joint European Torus | EPFL Graph Search

The Joint European Torus, or JET, is an operational magnetically confined plasma physics experiment, located at Culham Centre for Fusion Energy in Oxfordshire, UK. Based on a tokamak design, the fusion research facility is a joint European project with a main purpose of opening the way to future nuclear fusion grid energy. At the time of its design JET was larger than any comparable machine. JET was built with the hope of reaching scientific breakeven where the fusion energy gain factor Q =1.0. It began operation in 1983 and spent most of the next decade increasing its performance in a lengthy series of experiments and upgrades. In 1991 the first experiments including tritium were made, making JET the first reactor in the world to run on the production fuel of a 50–50 mix of tritium and deuterium. It was also decided to add a divertor design to JET, which occurred between 1991 and 1993. Performance was significantly improved, and in 1997 JET set the record for the clo

Particle transport in tokamak plasmas

Alexey Zabolotskiy

The transport of particles in magnetically confined plasmas is of great importance for the development of fusion energy. It will determine techniques for fuelling, for controlling impurity concentrations and for the removal of the alpha particles produced by fusion reactions. The issues related to particle transport have received, until relatively recently, less attention than those regarding heat transport. Besides the greater experimental difficulty of measuring particle transport, this may explain why our understanding of this subject is still incomplete. The aim of this thesis is to document and tentatively interpret the experimental density profile behaviour in the TCV (Tokamak à Configuration Variable) and JET (Joint European Torus) tokamaks in the framework of different theoretical and semi-empirical models. The TCV tokamak is well suited to transport studies due to its extreme shaping capability, which allows the exploration of a wide range of different plasma conditions. This versatility is matched by the powerful and flexible electron cyclotron heating (ECH) system on TCV, which allows a control of the local power deposition profiles and current drive profiles. A study of particle transport on the JET tokamak has allowed us to compare the results of TCV to those of a much larger device and supplement the TCV study with the analysis in reactor relevant high confinement regime (H-mode). The experimental information was compiled into a database of density profiles in steady state, containing nearly 1000 samples for TCV and 600 samples for JET. The data analyzed covered a wide range of discharge conditions, including low confinement regime (L-mode) and H-mode discharges, ECH, ICH (ion cyclotron heating), LHCD (low hybrid), beam heated plasmas and include fully current drive discharges. The most relevant parameters which influence the density profiles were determined by regression. A detailed analysis of the particle sources showed that edge fuelling in TCV and JET cannot be responsible for density gradient in the plasma bulk, confirming the presence of particle convection or a 'pinch'. The existence of an anomalous pinch was unambiguously demonstrated both on JET and on TCV by the observation of peaked density profiles in stationary, fully relaxed, fully current driven discharges and hence in the absence of the neoclassical Ware pinch. An unexpected difference in the parameter dependencies was found in L-and H-modes. In TCV and JET, density gradient lengths (or profile peaking parameters) in L-mode were found to depend on magnetic shear with no dependence on collisionality. This lack of collisionality dependence in L- mode is inconsistent with current theoretical models. H-mode density profiles in JET, on the other hand, are clearly dependent on collisionality in agreement with theory and a prior observation on ASDEX-Upgrade, while exhibiting only a weak or no dependence on shear and temperature profiles. It was found that for TCV and JET, L mode density peaking can be interpreted as being due to turbulent equipartition, which assumes conservation of the magnetic moment and the longitudinal invariant during transport. The observation of a reduction of peaking in TCV with ECH supports drift wave turbulence theory, which predicts the appearance of outward particle convection, when trapped electron modes are destabilized. In JET H-mode, the weak secondary correlation of peaking with the electron-ion temperature ratio Te/Ti, may also be considered, at least quantitatively, as being supportive of drift wave turbulence theory.

EPFL2005

Real-Time Processing System for the JET Hard X-Ray and Gamma-Ray Profile Monitor Enhancement

Patrick Blanchard

The Joint European Torus (JET) is currently undertaking an enhancement program which includes tests of relevant diagnostics with real-time processing capabilities for the International Thermonuclear Experimental Reactor (ITER). Accordingly, a new real-time processing system was developed and installed at JET for the gamma-ray and hard X-ray profile monitor diagnostic. The new system is connected to 19 CsI(Tl) photodiodes in order to obtain the line-integrated profiles of the gamma-ray and hard X-ray emissions. Moreover, it was designed to overcome the former data acquisition (DAQ) limitations while exploiting the required real-time features. The new DAQ hardware, based on the Advanced Telecommunication Computer Architecture (ATCA) standard, includes reconfigurable digitizer modules with embedded field-programmable gate array (FPGA) devices capable of acquiring and simultaneously processing data in real-time from the 19 detectors. A suitable algorithm was developed and implemented in the FPGAs, which are able to deliver the corresponding energy of the acquired pulses. The processed data is sent periodically, during the discharge, through the JET real-time network and stored in the JET scientific databases at the end of the pulse. The interface between the ATCA digitizers, the JET control and data acquisition system (CODAS), and the JET real-time network is provided by the Multithreaded Application Real-Time executor (MARTe). The work developed allowed attaining two of the major milestones required by next fusion devices: the ability to process and simultaneously supply high volume data rates in real-time.

Ieee-Inst Electrical Electronics Engineers Inc2014

Particle transport in JET and TCV H-mode plasmas

Mikhail Maslov

Understanding particle transport physics is of great importance for magnetically confined plasma devices and for the development of thermonuclear fusion power for energy production. From the beginnings of fusion research, more than half a century ago, the problem of heat transport in tokamaks attracted the attention of researchers, but the particle transport phenomena were largely neglected until fairly recently. As tokamak physics advanced to its present level, the physics community realized that there are many hurdles to the development of fusion power beyond the energy confinement. Particle transport is one of the outstanding issues. The aim of this thesis work is to study the anomalous (turbulence driven) particle transport in tokamaks on the basis of experiments on two different devices: JET (Joint European Torus) and TCV (Tokamak à Configuration Variable). In particular the physics of particle inward convection (pinch), which causes formation of peaked density profiles, is addressed in this work. Density profile peaking has a direct, favorable effect on fusion power in a reactor, we therefore also propose an extrapolation to the international experimental reactor ITER, which is currently under construction. To complete the thesis research, a comprehensive experimental database was created on the basis of data collected from on JET and TCV during the duration of the thesis. Improvements of the density profile measurements techniques and careful analysis of the experimental data allowed us to derive the dependencies of density profile shape on the relevant plasma parameters. These improved techniques also allowed us to dispel any doubts that had been voiced about previous results. The major conclusions from previous work on JET and other tokamaks were generally confirmed, with some minor supplements. The main novelty of the thesis resides in systematic tests of the predictions of linear gyrokinetic simulations of the ITG (Ion Temperature Gradient) mode against the experimental observations. The simulations were performed with the GS2 code. The parameter dependencies of plasma density gradient, as observed on JET, are a good agreement with those from the simulations over a wide range. The simulations done for the TCV case, which are in a different physics parameter domain, are also in partial agreement with the experiment. Complete agreement is not out of the question, but will remain a goal for the future, when measurements of one of the most important parameters will be available. The good agreement between the experiment and the simulations suggests that the ITG instability may be responsible for the majority of the anomalous inward particle convection observed in tokamaks. Both the simulations and the empirical data extrapolations predicting a peaked density profile in ITER plasma conditions, instead of a flat one, as was assumed during the concept design period.

EPFL2009