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ITER NEWSLINE 291
Recent experiments performed on the EAST superconducting tokamak in the Institute of Plasma Physics in Hefei, China have demonstrated the sustainment of high temperature plasmas in the so-called H-mode confinement regime over a record timescale of more than 30 seconds, as reported in the journal Nature Physics. The achievement of H-mode plasmas and their long-time sustainment will be key to the success of the ITER Tokamak and marks "another advance in fusion," says article author William Morris in his commentary. The long-pulse H-mode plasmas in the EAST tokamak have been achieved by heating the plasma with radio-frequency waves, such as lower hybrid waves.
While performing the recent experiments, the Chinese scientists led by Jiangang Li and Houyang Guo and their international collaborators from Germany, USA, France and the ITER Organization discovered that the application of lower hybrid waves had a strong and beneficial effect that reduced the repetitive energy releases by the plasma, which are characteristic of H-mode plasmas.
These energy releases are caused by "plasma outbursts" known as Edge Localized Modes (ELMs) and resemble solar flares. ELMs will have to be controlled in the ITER Tokamak because they cause the erosion of the plasma-facing components and significantly reduce their lifetime.
Experiments at EAST have shown that the effect of lower hybrid waves on the ELMs is due to the presence of electric currents at the edge of the plasma driven by these waves. These currents cause magnetic field "wrinkles" to appear in the external surface of the plasma, which otherwise has a smooth doughnut shape.
This innovative approach intrinsically provides a flexible control tool for ELMs over a broad operation space, and may open a new avenue for achieving steady-state high performance plasmas in future fusion devices if issues regarding its extrapolability to ITER and future tokamak reactors can be successfully resolved.
The use of small scale modifications of the edge magnetic field created by a set of coils external to the plasma to control ELMs was developed at the DIII-D tokamak in the USA and subsequently demonstrated worldwide in other tokamak experiments. It is now one of the two ELM control schemes considered for ITER. The recent results from EAST are the first to demonstrate this approach by modifying the edge magnetic field with currents created in the plasma itself without the need for external coils, thus confirming the universality of the physics mechanism leading to the control of ELMs by the approach adopted for ITER. Lower hybrid waves are being considered for ITER as an upgrade to be implemented after plasma operation commences.
Furthermore, the EAST experiments have demonstrated that driving local currents in the edge plasma by lower hybrid waves has some potential advantages with respect to the use of external coils in achieving ELM control. The use of lower hybrid waves not only facilitates ELM control over a large range of currents in the tokamak plasma, but also increases the area of the tokamak interior components over which the plasma deposits its energy in stationary conditions. This potentially offers a new means for heat flux control, which is a key issue for next-step fusion development.
EAST has ITER-like magnetic configurations and heating schemes, and will be one of the world's first magnetic fusion devices to address physics and technology issues facing high-power, long-pulse operation in high confinement regimes, thus providing a very timely test bed for ITER.
For Americans, Thanksgiving is a holiday that evokes family, a generously proportioned meal full of the flavours and colours of autumn, and an afternoon football match.
On Friday 22 November, a little ahead of the official date, the American members of staff shared some of the culinary traditions of Thanksgiving with their ITER colleagues. In a cafeteria festooned with flags and photographs and cheered by the music of the ITER band, the ITER community tasted corn chowder, turkey with stuffing and cranberry sauce, green beans, mashed potatoes, sweet potatoes, and apple or pumpkin pie.
Two distinguished guests joined the festivities: US Consul Diane Kelly from Marseille, and Ed Synakowski, Vice Chair of the ITER Council and Associate Director for Fusion Energy Sciences at the Department of Energy (Office of Science). As a commemorative slideshow played in the background, both had words to share on the legacy of John Fitzgerald Kennedy, America's 35th President assassinated 50 years earlier on 22 November 1963.
Celebrated each year on the fourth Thursday in November, Thanksgiving traces its origins back to the difficult conditions of the early settlers to the northeast coast of the United States. After a gruelling ocean crossing, the small group of Pilgrims that established the Plymouth colony (now Massachusetts) had little time to prepare for the harsh winter in New England and no knowledge of local fauna and flora. Half of the settlers died during the first winter.
In the spring, the early settlers were taught to fish and hunt locally as well as grow corn and distinguish edible plants from poisonous ones by a Native American. To celebrate the colony's first successful harvest and to give thanks for assistance received, the settlers invited their Native American allies to a feast that lasted three days.
The modern-day Thanksgiving holiday has evolved considerably from its humble beginnings. Celebrated every year since President Lincoln proclaimed Thanksgiving Day a national holiday in 1863, some 51 million turkeys (approximately one for every six people) are consumed every year on this day, and countless bushels of sweet potatoes, green beans and cranberries.
Click here to view the photo gallery of the US Day at ITER.
Following the successful Final Design Review for the ITER blanket in April 2013, the first of seven Procurement Arrangements for the blanket system were signed last week between the ITER Organization and the Chinese and Korean Domestic Agencies.
China and Korea will share the procurement of the blanket shield blocks—the "backside" of the 440 blanket modules that support the plasma-facing first wall and provide neutron shielding for the vacuum vessel and coil systems. These thick steel blocks, weighing up to four tonnes a piece, also have to accommodate interfaces with other components and in particular a large number of diagnostic systems. For this reason there are a total of 28 major design variants and 150 or more minor design variants.
"Last week's signatures were the culmination of several years of design and R&D effort on the part of the ITER Organization and the Domestic Agencies," says Rene Raffray, Blanket Section Leader. "Working together with the ITER Organization as part of the Blanket Integrated Product Team (BIPT), the procuring Domestic Agencies have been fully involved in the design since the start."
The first phase of Procurement Arrangement execution will be the call for tender to be launched in China and Korea to manufacture the first shield block prototypes based on procurement specifications and 3D drawings/2D assembly drawings provided by ITER.
"It has taken a lot of hard work, but it is rewarding and a credit to all those at ITER and in the Chinese and Korean Domestic Agencies who contributed to the achievement of these important milestones on time," says Raffray. "They are the latest in a list of on-time Blanket accomplishments that includes successfully going through the different system design reviews, and which have in great part been possible through active collaboration among the ITER Organization and the procuring Domestic Agencies within the BIPT framework."
Nuclear safety specialists from the European tokamak JET and ITER met in November to discuss the possible ways in which the practical experience of one experimental device could serve the planning stages of the other.
At JET, where 3,000 installable items and 16,000 tiles have been replaced inside the machine to equip JET with same materials mix chosen for ITER (beryllium and tungsten), the experiments underway since August 2010 are of interest not only to the ITER physicists, but also to the nuclear safety group at ITER.
"A more systematic collaboration between our teams could only be beneficial for ITER," stresses Joelle Elbez-Uzan, head of ITER's Nuclear Safety, Licensing & Environmental Protection Division. "We have many lessons to learn from JET operation and design. Collaboration would allow us to extrapolate important parameters for the safety analysis of ITER, in complement to our established safety case."
Joelle and her team are interested in all of the ramifications of operation with the ITER-like wall in JET, from the characterization and management of beryllium and tungsten dust, to in-vessel tritium retention and inventory, implications for worker safety during maintenance, and finally waste management.
"JET is the only European tokamak that has already injected tritium into its vacuum vessel," stresses Joelle "and the JET team is planning a deuterium-tritium campaign beginning in 2017 or 2019 depending on the selected scenario. Their safety considerations—for machine design, fabrication and operation—are much like ours."
During the meeting, potential areas for collaboration were discussed and agreed; in the coming months the ITER team will define and prioritize its specific needs. The type of collaboration to establish also remains to be defined.
"Our colleagues at JET are very open to sharing their experience with us—there are clearly areas of mutual interest. Capitalizing on JET's experience in the domain of nuclear safety will be extremely valuable for ITER."