A shattered pellet injector using the same technology as that planned for disruption mitigation on ITER will be tested soon on the JET tokamak at the Culham Centre for Fusion Energy (UK). Technical commissioning of the components is underway. At the Culham Centre for Fusion Energy in the UK, a global team has been working together to install and commission a shattered pellet injector on the European tokamak JET.   Contributors from US ITER, EUROfusion, the ITER Organization, Culham Centre for Fusion Energy, and Oak Ridge National Laboratory (with support from the US Department of Energy, Fusion Energy Sciences) are interested in testing the shattered pellet technique for disruption mitigation on the world's largest operating tokamak, after performing similar experiments at General Atomic's DIII-D machine (US), which has a plasma volume four times smaller.   "We are very excited to start testing the new shattered pellet injector on JET—it is a core part of EUROfusion's upcoming program," said Joe Milnes, JET Operating Contract Senior Manager for the UK Atomic Energy Authority. "The dedication shown by the project team to get the equipment installed and commissioned has been vital, and I'm sure they will feel immensely proud when the first shattered pellets are injected and the first results are published."   In order to produce a self-heated, burning plasma on ITER, a disruption mitigation system is essential. Plasma disruptions can produce large heat loads, electromagnetic forces, and runaway electron beams. After investigating different designs, ITER partners concluded in a 2017 international workshop that the injection of frozen pellets of deuterium, neon, and/or argon will be the baseline method for the ITER system. Experiments on the DIII-D tokamak in San Diego, California, produced findings that shattered pellet injection leads to more effective thermal mitigation than another technique that was investigated—massive gas injection—with deeper penetration of the fragment spray.    The three-barrel pellet injector can shoot three distinct pellets, sized from 4.5 mm to 12.5 mm, depending on the experiment. "The extrapolation of shattered pellet injection performance to ITER is greatly enhanced by employing an injector on JET to see how the mitigation metrics scale with plasma size and energy. This will give us higher confidence in the predicted mitigation outcome on ITER," said Larry Baylor, distinguished scientist at Oak Ridge National Laboratory's Fusion Energy Division. "A unique feature of JET is that it has an ITER-like wall of beryllium and tungsten, which influences disruption behavior."   Shattered pellet injection involves cryogenically freezing pellets of deuterium, neon, argon, or some combination in a specially designed cryogenic "pipe gun." The pellet is injected into the plasma at speeds of 500-1800 km per hour when a disruption is detected. By shattering the pellets in a curved tube before the material enters the vacuum vessel, it is possible to form collimated sprays of pellet material that penetrate deeply and rapidly into the plasma. For ITER, a sufficient quantity of material must be delivered to the plasma when a disruption is detected, as the ITER plasma volume is ten times greater than JET's. This quantity will be achieved with multiple shattered pellets and multiple injectors.   The shattered pellet injector installed on JET is similar to those planned for use on ITER, but scaled to JET plasma parameters. The injector will utilize three distinct pellets, sized from 4.5 mm to 12.5 mm, depending on the experiment.   "The experiments will help answer questions about whether shattered pellet injection will remove energy from the plasma fast enough and uniformly enough to effectively mitigate disruptions in a large tokamak," said Baylor. "We'll also learn how the physics of shattered pellet injector disruption mitigation scales to larger, more energetic plasmas."   Planning is already underway for other injector experiments on the KSTAR tokamak in Korea. In the KSTAR experiments, two identical 3-barrel shattered pellet injector systems will be deployed to mimic the planned multi-injector approach at ITER. These experiments are part of the efforts of the ITER Disruption Mitigation Task Force to validate design choices for the ITER system and to develop the technology to an industrial level to face the challenges in the ITER environment.

Final assembly activities on the first toroidal field coil to be shipped to ITER are well underway in Japan. The insertion of the superconducting winding pack into its structural case was achieved in March through the successful collaboration of Mitsubishi Heavy Industries, Ltd. (MHI) and Mitsubishi Electric Corporation (MELCO).  The National Institutes for Quantum and Radiological Science and Technology (QST*) is responsible for procuring 9 of ITER's 19 toroidal field coils. It has contracted with MHI and MELCO for five of the coils and with Toshiba Energy Systems & Solutions Corporation for four others.   Over two and a half weeks in March, MHI/MELCO successfully carried out the Japanese procurement program's first insertion operation—a highly delicate sequence of activities during which the 110-tonne D-shaped superconducting winding pack is inserted into its structural steel case.   QST's contractors have chosen a vertical insertion approach and developed an assembly platform and handling tools accordingly.   At the start of the operation, case manufacturer MHI positioned one side of the steel casing—the 16-metre, linear inboard leg—on the platform facing up. MELCO (responsible for the fabrication of the superconducting magnet core) oversaw the lowering of the winding pack by crane, continually monitoring its position within the case leg by precision laser tracker over the hours-long operation. Fine adjustments were made to the position of the winding pack in order to reach required tolerances within an accuracy of 0.3 mm.    It was then MHI's turn to carefully lower the 130-tonne curved outboard leg over the vertical assembly. Four guide pillars installed on the sides of the winding pack prevented the component from causing damage as it descended to rest on four temporary supports. Equipped with 3D positioning adjustment capabilities, the supports allowed the outboard leg to be adjusted precisely to match the weld bevels of the inboard leg within tolerances of +/- 0.5 mm over a length of 16 metres.   Once matched, four welders worked simultaneously to balance welding shrinkage and maintain any deformation to less than 3 mm as they welded the two halves of the coil case together. The precision laser tracker was called into action again to monitor the coil case shape during the entire process, allowing real-time adjustments to the weld paths in response to the actual deformation observed. With this careful technique, deformation over 9-metre-wide coil was optimized to 1.5 mm.   The success of the first winding pack insertion operation in Japan confirms the technologies and tooling of the selected technique and demonstrates that QST contractors can meet the tight tolerances required. This is excellent news, as work is proceeding In Japan on the fabrication of eight other ITER toroidal field coils.At MHI's Futami plant, the next step will be to install and weld the inner covers that complete the case assemblies (see the AP and BP components in the diagram here) and finally to inject resin to fill any space between the winding pack and the coil case. With the strong collaborative effort between MHI and MELCO, the Japanese Domestic Agency is confident of meeting these challenges in full respect of all project specifications.

A few days ago, one of the Titans in the Assembly Hall woke up and flexed its little finger. The movement was slow, almost imperceptible. Like in a living body, nerves and muscles (in the form of signal cables and hydraulic pumps) coordinated their action to lift and lower one of the upper alignment units at the top of the giant sector sub-assembly tool—one of the first steps in the mechanical tests program being performed on the spectacular, 20-metre high twin Titans. The sector sub-assembly tools (SSAT) are the largest tools in the ITER assembly panoply. Their task is to pre-assemble a vacuum vessel sector with its thermal shield and two toroidal field coils. Opening and closing their arms, adjusting the position of their upper and lower alignment units, they will repeat sub-assembly operations nine times, once for each of the Tokamak's nine vacuum vessel sectors.   The pre-assemblies, weighing approximately 1,200 tonnes, will then be transferred to the assembly pit by way of a double overhead gantry crane to be integrated into the machine.   Before this can happen, however, two major milestones need to be accomplished: the completion of full mechanical and load tests on both SSATs, and the erection of a steel structure over of the Tokamak Building to "close over" the Tokamak Pit and allow the Assembly Hall crane bays to be extended.   Load tests are scheduled to begin in early June, and preparation work has already started for the extension of the crane bays.   Click here to view a video of the Titan's awakening.

A small tokamak changed hands in July of last year. HT-6M, a circular limiter machine developed at the Chinese Institute of Plasma Physics  (ASIPP) in the 1980s, was pulled out of retirement to start a new life at the Thailand Institute of Nuclear Technology (TINT). The southeast Asian kingdom, which depends heavily on fossil fuels to cover the electricity needs of its population of 69 million, made its first steps into fusion research in 2015 when a series of conferences was organized in Bangkok by specialists from the French Institute for Magnetic Fusion Research (IRFM).   "The original idea was to expose the younger generation to the challenges and promises of fusion," explains Tuong Hoang, a fusion physicist and international relations expert at IRFM. "Interest was strong and growing, not only in Thailand but also in neighbouring countries like Nepal, the Philippines or Indonesia. At one point, we began discussing with our Chinese colleagues at ASIPP about the possibility of donating HT-6M, as it makes sense to have a tokamak when you are studying magnetic confinement fusion..."   Fusion research in Thailand has a strong proponent in Princess Maha Chakri Sirindhorn, the king's sister, who presided over the handing over of HT-6M in July 2018 and visited ITER a few months later. On the occasion of her visit, a Cooperation Agreement was signed between the ITER Organization and TINT.   Participants to the 4th edition of the ASEAN School on Plasma and Nuclear Fusion (ASPNF) at Mahidol University, Thailand, in January 2019. IRFM and ASIPP specialists, now joined by Japanese colleagues from the Large Helical Device, are involved in the ASEAN School on Plasma and Nuclear Fusion (ASPNF) they contributed to establishing. "The objective is to train a first nucleus of 20 to 30 physicists and engineers through a five-year program," explains Tuong. "The first class is presently in its second year of training and will soon be ready to practice on HT-6M."