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Fusion
Published in William J. Nuttall, Nuclear Renaissance, 2022
Japan meanwhile has had a very long history of engagement with tokamak fusion research being home to one of the three large tokamaks of the 1990s: the JT-60 tokamak. First conceived in the 1970s the JT-60 machine has been through numerous upgrades. The latest variant, JT-60SA, a collaboration with the European Union, incorporates superconducting technology, and in March 2021, it reached its design goals in terms of toroidal magnetic field [73].
Actuator Development Step by Step: Pellet Particle Flux Control for Single- and Multiple-Source Systems
Published in Fusion Science and Technology, 2022
P. T. Lang, B. Ploeckl, R. Fischer, M. Griener, M. Kircher, O. Kudlacek, G. Phillips, B. Sieglin, S. Yamamoto, W. Treutterer, AUG Team
The JT-60SA is a large superconducting tokamak device in its commissioning phase. It will be at the forefront of the international fusion program, supporting the ITER experimental program as a satellite machine. In addition, it is expected to provide key physics and technology information for the operational scenario of future DEMO fusion reactors, in particular for a steady-state, advanced-performance design option. With respect to this, it requests a powerful and versatile pellet injection system that at least is expected to serve simultaneously for its particle fueling and ELM pacing experiments. Following this request, a conceptual design was worked out for a suitable PLS (Ref. 23), which is now under construction. It is based on the stop cylinder centrifuge principle of the AUG PLS (Ref. 12), but is going to extend it further. For the pellet sources, it will apply an advanced and more reactor-relevant technology using quasi-steady-state extruders capable of delivering pellets continuously for the entire plasma duration of up to 100 s. The extruder layout offers the option to operate with both stable hydrogen isotopes but also with admixed gases. Hence, they can be operated as a seeding source on demand. Furthermore, these multiple pellet sources have to be controlled in parallel. In the startup configuration, the PLS will incorporate two extruders (one for fueling, one for pacing); the layout made can host three extruders, so their control system has to be construed accordingly. For the controlling of the pellet launch, in order to avoid pellets colliding and damaging each other, it must take into account that only a single pellet can be put into any launching slot. This enforces a priority ordering of all tasks, determining which one gets accepted in case of simultaneous requests. Too, possible cross talk between different actuations has to be taken into account. For example, modeling showed ELM pacing pellets can increase the density considerably and thus result in an unwanted density overshoot.24 Hence, the ultimate control task is to decide which launching slot has to be occupied and by which pellet. As a result, it will compose a single train of different pellets most suitable for all activated tasks.