There was a time in fusion history when the hopes of harnessing the power of the stars rested on a device aptly called a "stellarator." Shaped as a figure-eight torus, the stellarator was the brainchild of a 37-year-old American astrophysicist named Lyman Spitzer.   How Spitzer had a revelation for this particular design belongs to the legend of fusion. It all came to him as he was skiing in Colorado, pondering the claim that an Austrian scientist, working for Argentina's strongman Juan Perón, had just produced "the controlled liberation of atomic energy" through the simplest and lightest of all elements, hydrogen.   Argentina's claim was soon to prove a hoax. But Spitzer's concept, born on a ski slope in early 1951 and turned into an operational device (the "Model A" stellarator) in the fall of 1952, was to rule supreme among fusion devices for almost two decades until it was dethroned by a Soviet invention ─ the tokamak.   Soviet physicists began developing tokamaks in the late 1950s. By the end of the following decade, the performance of the Soviet machines was a full order of magnitude higher than any other fusion device.   As the tokamak concept took centre stage, stellarators were abandoned or transformed into tokamaks. And the tokamaks, for their part, became more promising as they progressively grew larger and more powerful.   Yet stellarators still had their aficionados, and in the late 1980s—thanks to spectacular progress in computer-aided design, automation and engineering techniques—the stellarator was given a second chance.   At the Max Planck Institute of Plasma Physics in Germany, the Wendelstein 7-AS entered into operation in 1988 and pursued a brilliant career until 2002. Japan followed suit with its Large Helical Device (LHD), which celebrated first plasma in 1998. In the US, a small stellarator—the Helically Symmetric Experiment (HSX)—was built at the University of Wisconsin at Madison in 1993 and a much larger device, the National Compact Stellarator Experiment (NCSX), was launched at the Princeton Plasma Physics Laboratory in 2004 only to be cancelled four years later by the US Department of Energy.   Stellarators rely on a complex and baroque arrangement of twisted coils to confine the plasma inside the machine's vacuum chamber. Wendelstein 7-X is expected to begin operations in the coming weeks. Image: Adapted from IPP by C. Bickel/Science magazine Now, almost 65 years after Spitzer's skiing trip to Colorado, a new age may be dawning for the stellarator. In northern Germany, the successor of Wendelstein 7-AS, dubbed "7-X," is on the verge of entering operations.   The German machine, in the words of science writer Dan Clery (in Science), looks "a bit like Han Solo's Millennium Falcon, towed in for repairs after a run-in with the Imperial fleet."   Contrary to tokamaks, with their symmetrical and rather straightforward architecture, stellarators rely on a complex and baroque arrangement of twisted coils to confine the plasma inside the machine's vacuum chamber.   The essential difference between a stellarator and a tokamak is that a tokamak has a central solenoid which induces current in the plasma that twists the magnetic field lines and increases plasma stability. In contrast to the tokamak device, a stellarator has no central solenoid, there is no current driven in the plasma. The twisting of the magnetic field lines is created by complex shaped external magnetic coils instead. This configuration gets around many of the difficulties encountered in tokamaks, however, significantly complicates the design and construction of such a device.   Source: Wigner Research Centre for Physics "This extremely complex geometry and the manufacturing challenges it generates are the main drawbacks of stellarators," says Rem Haange who was Technical Director of Wendelstein 7-X from 2005 to 2011 before becoming Deputy Director-General and Head of the ITER Project Department at the ITER Organization.   But stellarators have an advantage ─ they are inherently stable. In a Newsline interview in 2011, Thomas Klinger, who heads the Wendelstein 7-X project, used the following image:  "In a stellarator, confining the plasma is like holding a broomstick firmly in your fist; in a tokamak, it's like trying to balance the same broomstick on your finger."   In a few weeks, the German machine will demonstrate how well, and for how long, it can hold the broomstick. Rem Haange is confident. "The design of Wendelstein 7-X was driven by how to improve plasma confinement. We concentrated on how to minimize particle loss and, according to computer models, the machine should meet our expectations."   Does that mean that stellarators will one day provide an alternative to tokamaks? In the timeline of fusion devices development, Wendelstein 7-X stands where JET (the largest operating tokamak today) stood 32 years ago ─ a promising device whose size and technology will open new territories to explore ... but still a long way to an industrial-size installation like ITER.   In the longer term, all will depend on Wendelstein 7-X's results. "After all, we have developed both diesel and petrol vehicles and they both perform to our satisfaction," says Haange. "It's possible to imagine a future where stellarators and tokamaks cohabit in harmony."  

In India, at M/s. Avasarala Technologies Limited in Bangalore, manufacturing activities for the ITER vacuum vessel in-wall shielding are progressing.   The first factory acceptance tests on in-wall shielding components were carried out in June 2015; since then a total of four have been completed. These milestones open the way for shipment of the components to vacuum vessel manufacturers.   As part of procurement for ITER, India is responsible for manufacturing the in-wall shielding block assemblies that will be integrated into the vacuum vessel by suppliers in Europe (responsible for seven vacuum vessel sectors) and Korea (responsible for two). This includes the shield blocks themselves as well as support ribs, brackets and fasteners—some 8,000 individual components in all.   Factory acceptance tests have been completed for 320 shield blocks, 144 machined support rib lower bracket assemblies, 102 welded support rib lower bracket assemblies, 106 studs, and 16 platforms by a joint inspection team comprising of members from the ITER Organization, the European and Korean Domestic Agencies, and the Indian Domestic Agency.   As reported here, the first container of 48 support rib lower bracket assemblies has already been shipped to Korea for vacuum vessel Sector 6. Other components will ship out to the vacuum vessel manufacturers in Europe and Korea as soon as the factory acceptance test process is complete.

​In the space between the double walls of the ITER vacuum vessel, poloidal and toroidal stiffening ribs will provide structural support for the vacuum vessel and also form the flow passages for the cooling water. Approximately 55 percent of the space will also be filled with in-wall shielding—modular blocks weighing up to 500 kg each that protect components situated outside of the vacuum vessel from neutron radiation.   In Korea, where two of the nine ITER vacuum vessel sectors will be manufactured, the in-wall shielding blocks will be pre-assembled into the sector through the support rib. These in-wall shielding blocks, plus all related components such as support ribs, brackets and fasteners, fall under the procurement responsibility of India. On 20 October, the first container of material was received from India at Hyundai Heavy Industries in Ulsan, Korea. Site acceptance tests were successfully completed the same day for all 48 in-wall shielding support rib bracket assemblies for one of the poloidal segments of vacuum vessel Sector 6 in the presence of representatives from the ITER Organization, the Korean Domestic Agency and Hyundai. The container had left Chennai harbor in India on 30 September. This is the first delivery related to the ITER vacuum vessel received by Korea from other ITER Domestic Agencies

All kinds of equipment—magnet feeders, cooling water system tanks, diagnostic systems, cryolines, cable trays—need to be attached to the walls, floors and ceilings of the Tokamak Complex.   But for structural reasons, as well as for nuclear confinement, you can't drill holes to attach pegs, hooks or shelves in a nuclear building.   The solution comes in the form of embedded plates that are welded deep into the rebar lattice and are capable of supporting loads of up to 90 metric tons in pure traction (for the largest of them).   All in all, 80,000 embedded plates are planned in the Tokamak Complex. In some cases, they can be pre-installed in the reinforcement "cages" and welded with utmost precision once the cage is in its final position on the building site.   This picture captures the spectacular "flight" of a reinforcement cage as it is lifted from the prefabrication area to be delivered to the workers responsible for the Tritium Building area, on the northeast side of the Tokamak Complex.

​Mechanical Engineer Jeff Doody from MIT's Plasma Science and Fusion Center (PSFC) received a "Best Paper Award" on 9 October at the COMSOL Conference 2015. The paper, "Structural Analysis of the Advanced Divertor eXperiment's Proposed Vacuum Vessel," describes how Doody used COMSOL Multiphysics modeling software to predict loads and stresses on the vacuum vessel in the initial design for the Advanced Divertor eXperiment (ADX), a proposed high field, high-power-density fusion tokamak. Collaborating with him at the PSFC were Chief Mechanical Engineer Rui Viera, Senior Research Scientist Brian LaBombard, Principal Research Scientist Bob Granetz, Mechanical Design and Fabrication Specialist Rick Leccacorvi, and Principal Research Engineer Jim Irby. Photo: Mechanical Engineer Jeff Doody of ​MIT Plasma Science and Fusion Center. Read the whole article on the PSFC website.

​The complex puzzle that makes up MAST Upgrade's main plasma heating system is well on the way to completion at the Culham Centre for Fusion Energy (CCFE) in the UK. The neutral beam injection system will provide most of the heating power for MAST Upgrade (around 5 megawatts). It works by firing fast-moving neutral particles into the plasma, where their motion is transferred into heat. Recent work has focused on the system's bend magnets and ion dump assemblies. These components steer stray charged particles away from the heating beam and absorb their energy, which can be as much as 12 megawatts per square metre — much more than the loads on spacecraft re-entering the atmosphere. The bend magnets were delivered to site during the summer and passed acceptance testing before undergoing a trial fit in the neutral beam injection tanks to check their alignment. Meanwhile, the build of the welded ion dump assemblies has proceeded well throughout the year. By the end of 2015, the pre-assembly of these components will be complete, leaving them ready for installation into the tanks. The re-build of the neutral beam injection system will take place in 2016. Read the original article on CCFE's website.

Operation since 1988, the CEA-Euratom tokamak Tore Supra (France) is undergoing a major transformation in order to serve as a test bench for ITER—the WEST project.   Equipped with a new, actively-cooled tungsten divertor, WEST will test tungsten technology, acquire data on metal fatigue, and explore the component boundary conditions in advance of ITER.   As early as 2016 the machine will be ready to test the first samples of plasma-facing units—an arrangement of small tungsten blocks that, once assembled, will form the new divertor.   The recent installation of the lower divertor coil box marked an important step in this direction. © Christophe Roux CEA-IRFM   Visit the WEST website here.