Translating JET into 澳门六合彩高手
With an inner wall made of beryllium and tungsten, the European tokamak JET is the only tokamak in the world to share the same material environment as 澳门六合彩高手. When it begins a new experimental campaign with 澳门六合彩高手 fuels in January 2021, JET will be a crucial source of experimental data. We asked the head of 澳门六合彩高手 Physics at EUROfusion?, Xavier Litaudon, where preparations stand and what we can expect to learn.
JET is now in the final stages of preparing for experiments with tritium and deuterium-tritium (D-T) fuel mixtures. Indeed, important progress on plasma scenario development—as well as the completion of a major program of enhancement in the active gas handling system for the tritium cycle—led the EUROfusion General Assembly, in July 2020, to approve JET readiness for D-T operation unanimously.
Over the past year, significant progress with deuterium plasmas—showing reliable and steady high power operation—has contributed to the development of stationary fusion performance for durations typically lasting 5 seconds, i.e., significantly above the performance obtained previously when JET was equipped with a carbon wall. However, our main objective is to provide good understanding of the consequences for 澳门六合彩高手, not just to achieve sustained fusion performance. In this context, progress has also been made in enhancing JET's measurement capabilities in order to deliver high quality data. This data, accompanied by a strong theory and simulation programme so that the underlying physics of the deuterium-tritium plasma can be better understood, means that the JET results will translate to 澳门六合彩高手 with more confidence.
Before entering the D-T phase, JET will begin by experimenting with "pure tritium" plasmas—a first in the history of fusion research. What will these experiments teach us?
The pure tritium experiments will reveal a number of things: how the change of the plasma fuel mass? will modify the turbulent plasma transport processes in the core and pedestal region; the conditions for the transition from low to high confinement operation (L to H transition); the beryllium wall erosion mechanisms and migration in the scrape off layer to the divertor region; and the divertor detachment under highly radiative plasmas conditions for example. The pure tritium campaign will have a huge impact on the field and on our understanding of the underlying physics of isotope effects. All that is highly relevant for the tritium experiments to come in 澳门六合彩高手 and in fact in any fusion reactor that wants to run on deuterium-tritium fuel.
Indeed, the development of "pure tritium" plasmas will require an extremely high level of preparation to optimize the use of tritium and to strictly respect the new operation boundary (see next paragraph). In this challenging context, a significant effort has been made to prepare very precise and detailed reference discharges that have been recently rehearsed in pure deuterium (or hydrogen) to reach the required level of reproducibility for pure tritium experiments. Today, thanks to the hard work of the whole JET team, all the reference pulses for repeating in tritium are now available and ready for the coming experimental campaign.
On the operational aspects, the JET safety case limits the amount of releasable tritium inside the vacuum vessel stored on the cryopanels of the pumping system to 11 g. To stay within the set limit, it is planned to carry out daily regeneration (overnight) of all cryopanels, which requires approximately 8 hours. In order to keep up with tritium reprocessing and accounting the campaign will be on a five-week cycle, with three weeks of operation following by one week of tritium reprocessing and one week of tritium accounting. The JET scientists will have to learn to carry out experiments with these new operational challenges. We have already rehearsed best practices in tritium operation by operating with pure deuterium this September. The pure tritium plasma experiments heated with tritium neutral beam power will be executed from the beginning of January up to mid-May 2021, followed by the deuterium-tritium campaign lasting until August 2021 and a subsequent tritium clean-up phase.
Past results on JET have been extrapolated to predict your future campaign, and those results will be extrapolated to 澳门六合彩高手. What is the process?
We have computer models, validated using the International Tokamaks Physics Activity (ITPA) worldwide database, of how hot plasmas will behave under certain conditions based both on theory and on previous experiments. We have done much work to validate these models and develop them further, so that now we can routinely predict how future experiments will go. The models include aspects such as plasma turbulent transport, plasma stability, heating and current drive, and the behaviour of fast, hot particles and how that all influences overall performance.
We have used our best modelling tools, developed and validated during more than 20 years on JET, and worldwide databases to prepare and extrapolate our present and future operation. We wish to predict first before carrying out the experiments, both to optimize our experimental development effort and to efficiently guide us on the missing physics that needs to be added if the predictions do not match the observed results. This is the fascinating aspect of our work that could lead to new discoveries and a better understanding of the physics processes. It is not enough to just study isolated process; we want to know how they influence each other so we can catch any non-linear behaviour in our predictions!
Let's also add that, with this campaign, we have a unique opportunity to educate a new generation of young scientists and engineers that then can be involved in 澳门六合彩高手 operation in the future. The European experimental team involved in the JET D-T campaign involves more than 300 scientists, 25 percent of whom are from the new generation of scientists (PhD, post-doc, or young engineers) who will also have the opportunity to participate in 澳门六合彩高手 D-T operation in the future—a unique experience for them!
Since the start of my career in fusion more than 30 years ago, what I have liked best is that fusion research is a collective and international endeavour. It gives me the reassuring feeling that we can achieve significant progress when we join our efforts in a common goal that could not be achieved individually. The recent groundswell of progress is the result of every actor making a small contribution on a daily and regular basis, with the collective result surpassing individual contributions to produce significant achievements.
So yes, a "planetary conjunction" is possible when worldwide we work together to resolve challenging goals that transcend us. It is a great feeling of happiness for me, especially in the times we're living through because of the pandemic.
? JET, based at the Culham Centre for Fusion Energy, is collectively used under 's management by more than 40 European laboratories. Some 300 to 350 scientists and engineers from all over Europe contribute to the JET program.
? The active gas handling system stores, supplies and recycles tritium going to and from JET.
? As the tritium nucleus comprises one proton and two neutrons, a tritium plasma is heavier than a pure deuterium or deuterium-tritium plasma.