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Internal image of the three-barrel repeating pneumatic deuterium pellet injector used on DIII-D for pellet ELM pacing experiments. Photo: US ITER/ORNL
Using a cryogenic deuterium pellet injector installed on the DIII-D Tokamak operated by General Atomics in San Diego, Oak Ridge National Laboratory (ORNL) researchers and collaborators were able to fire millimetre-sized frozen deuterium pellets into ultra-hot plasma at a rate of 60 times per second. The results demonstrate that pellet technology can repetitively trigger small edge instabilities that both protect material surfaces from potentially larger energy pulses and help to keep the plasma free of impurities. This is the first time the technique has been demonstrated at a level nearing the requirements of ITER.

"Our recent experiments indicate that the newly tested pellet injection technique can be applied at pellet repetition rates approaching what ITER needs and without harmful effects," said Larry Baylor, a plasma physicist and engineer at ORNL's Fusion Energy Division, who led the collaboration of researchers from General Atomics, the ITER Organization, Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, and the University of California San Diego. The US Domestic Agency (US-ITER) is responsible for developing and fabricating pellet injectors and pellet-based ELM pacing technology for the ITER machine.

The team has demonstrated that it is possible to decrease the intensity of the periodic plasma edge disturbances, known as edge localized modes (ELMs), by a factor of 10 by injecting small pellets at a 10 times higher frequency than the ELMs naturally occur in the plasma, Baylor said in an interview.

"You have seen pictures of the sun, in which part of the hot plasma surface flies out and into space? That is in some sense similar to what happens to a tokamak plasma on its outer edge, its boundary," Baylor explained.

When large flare-like events occur, they can cause erosion and melting of the metal surfaces that surround the plasma, causing metal impurities of beryllium or tungsten in ITER to enter the plasma and thereby reduce its energy and performance.

"That's a byproduct of having the wall in close proximity to the plasma," Baylor said. "The magnetic field is not a perfect container. The plasma does leak out. And when it contacts the wall it can release these impurity atoms that then can find their way into the plasma. We have to minimize that."

To reduce the size of the ELMs, researchers used a cryogenic deuterium rapid-fire "machine gun" that fires 1.3 mm deuterium ice pellets into the edge of the plasma, at up to 60 Hz, or 60 times per second. Each ice pellet triggered a small ELM, short-circuiting the plasma's natural tendency to have infrequent, large ELMs. Using this rapid-fire technology, they are in effect "tickling" the edge of the plasma, Baylor explained, to turn potentially large and damaging ELMs into a series of small ones that can do little or no harm.

"It really is a machine gun. And we had three of them operating together, each one firing 20 times per second," Baylor explained. "We fired these simultaneously, alternating among them. We ended up with 60 pellets per second entering the plasma, and these stimulated much smaller ELMs than would occur naturally."

The researchers observed, as they expected, that the more frequently that ELMs occur, the smaller they tend to be and consequently the smaller the pulsed energy losses from the plasma. It benefits the plasma to create multiple small incidents and the researchers are taking advantage of this insight. "If they flare out once per second, then they are very big. But if they are ejected at 60 times per second, then they are very small," Baylor said.

Not only did the researchers successfully demonstrate that their method for controlling plasma edge activity is potentially feasible for ITER, but they also found that their intervention did not negatively affect the plasma's internal energy, Baylor said. This was somewhat unexpected. "The plasma performance was essentially the same as it was without the pellets."

Furthermore, Baylor said, they found that such pellet injection actually made the plasma cleaner: The injected pellets stimulate the flow of particles on the outer boundary of the plasma downwards along the lines of the magnetic field and towards the divertor at the bottom of the plasma vessel, where the heat flux exits the tokamak.

The divertor is a kind of funnel on the floor of the container that pumps out impurities, metal and carbon atoms and ions from the plasma. "By injecting pellets and causing particles to flow down to the divertor, [the pellets] act as a screening mechanism to keep those impurities reduced, to keep them from migrating into the plasma. So it resulted in a much cleaner plasma, more pure than would otherwise be the case. We weren't expecting this at the level that we discovered," Baylor said.

The testing of the technology at the DIII-D facility demonstrates proof of principle on a system that is about one-tenth the pellet throughput that ITER will require. While the plasma on DIII-D is sustained for a matter of seconds, the plasma in ITER will run for up to an hour.

"The scaling up to ITER represents a challenge in that we have to use larger pellets," Baylor said. "So the throughput of solid deuterium, the continuous extrusion that we create to make the pellets, is more of a challenge."

"The challenge is also in producing that much solid deuterium that is at a temperature of 15 K. ITER will not require 60 pellets per second, as we did here; it will need perhaps 20 pellets per second. But they will be much larger pellets, something more like 3 mm in size."

"It's like a BB-size, or slightly bigger, whereas the size used here in testing was only 1.3 mm, so on the order of 10 times smaller."
Moving forward, the researchers now are planning to inject pellets from the inner wall to fuel the plasma and at the same time to control edge localized plasma flares with injection from the outer wall.

"In the future in ITER, we will have to replenish the plasma [with fuel], because the duration of the plasma will be so much longer that we must replenish both the burned and slowly leaking plasma particles," Baylor said.

"Our goal is to demonstrate that we can inject fuel pellets synergistically with ELM pacing pellets and maintain good plasma performance. This is what ITER will require."



Experts at the Brussels workshop on science communication stressed that quality and honesty of information, as well as openness, are key. Here, the ITER stand at Foire Internationale de Marseille in September 2010.
The ITER Organization was invited at a workshop in Brussels on Wednesday 25 April to discuss possible orientations for the European Union's (EU) Horizon 2020 Framework Programme, which is likely to make EUR 80 billion available for research projects in a range of selected areas such as climate change, sustainable transport, energy, and food safety. Horizon 2020 will run from 2014 to 2020 and is the EU's flagship initiative aimed at securing global competitiveness.

Interestingly, Horizon 2020 will be open to scientists and industrialists from countries all over the world—not just from Europe.

The workshop was organized by Germany's Fraunhofer Institutes, with a view of providing feedback from various experts to the European Commission, which has the responsibility to propose new EU initiatives.

This was a very constructive workshop, as it addressed many issues that are also relevant to ITER.

For example, one interesting feature of Europe's Framework Programmes is that they support "science and society" activities, i.e., research on gender issues, ethics, and science communication. As Maire Geoghegan-Quinn, the current EU Commissioner for research and innovation, put it: the aim of these activities is "to engage people and civil-society organizations in the research and innovation process" in order to lead to lead to responsible research and innovation.

I was invited to contribute to the workshop and take part in a discussion about future activities in science communication. What are the key challenges in this field? What kind of issues or problems are better addressed through European and international collaboration? Obviously the goal was to identify possible actions at the EU level but it is well known that the decisions taken in Brussels also send strong signals worldwide.

To start with, the results of a public consultation in the EU were disclosed during the meeting. They showed that two-thirds of respondents agree that "science communication will be an integral part of the duties of all European scientists."

Good communication is crucial for major scientific and technological endeavours. Scientists should take an active role (with the help of professional communicators) but this is not the end of the story. Public debates and TV programs on science issues do not always get scientists involved.

Most of these issues are complex ones and the scientific information does not always reach the public. It is not only a matter of communicating the facts, but also making sure that the public understands how scientific knowledge is built, what research is behind the science, etc. This is a big challenge, including for the ITER Project. Experts at the meeting stressed that quality and honesty of information, as well as openness, are key.

One thing is clear: science communication is emerging as a genuine scientific field. Academic research, as well as European and international cooperation, has provided powerful insights on how to engage with the public on science issues. So, what's next? It will be interesting to see to what extent the discussion in Brussels will shape Horizon 2020, which should be adopted at the end of 2013 by the EU Council of Ministers and the European Parliament.

 
Michel Claessens is coeditor of a just-published book titled 'Science communication in the world.'

Under the eyes of Homi Jehangir Bhabha, scientist and visionary, Shishir Deshpande and Osamu Motojima signed Procurement Arrangement 71 at the Old Yacht Club in Mumbai.
Work on yet another ITER procurement is about to commence in India. At the iconic Old Yacht Club in Mumbai, hometown of the Indian Department of Atomic Energy, ITER Director-General Osamu Motojima and Shishir Deshpande, the Head of the Indian Domestic Agency, signed the Procurement Arrangement for ITER's cryodistribution system last week.

The main role of the cryodistribution system is the controlled distribution of cryogenic helium to the cold-loving clients within ITER, such as the superconducting magnets, the cryopumps and the thermal shields. The contract covers the finalization of the design and the manufacturing, installation and testing of the entire cryodistribution system on the ITER site ... terminating with the final commissioning of the components in 2019.

The cryodistribution system represents the fourth and last in-kind Procurement Arrangement for ITER's cryogenic systems; it is also the third signed with India. One in-cash Procurement Arrangement remains for the liquid helium plant, which is to be signed later this year.


ITER Director-General Osamu Motojima (right) and the president and CEO of KEPCO E&C, Seung-Kyoo An, after signing on the dotted line.
At ITER, there will be over 6,000 kilometres of cables which have to find their optimum routing path inside the 100-kilometre-long network of cable trays. This service contract was awarded this week, 30 April, in Seoul to the Korean company KEPCO specialized in the construction of nuclear power plants. Last week, ITER Director-General Osamu Motojima and the president and CEO of KEPCO E&C, Seung-Kyoo An, signed on the dotted line.

The contract covers the design of the cable trays for the whole ITER installation, including: seismic analysis and supporting structures; routing of all the cables; production of bill of materials for cables and cable trays; production of the manufacturing drawings for cable trays; and cable installation reports. In addition, this contract will provide support to the systems for the cable data collection, development of cabling and termination diagrams.