The American Association for the Advancement of Science (AAAS), the world’s largest scientific society and one of the oldest (founded 1848), held its annual meeting on 14-18 February in Boston.
The meeting, which a US newspaper described as „the largest aggregation of pointed heads anywhere,” is quite unique in its breadth and scope. The topics range from biology to cosmology and from elementary particle physics to science communication, covering the whole range of science research and knowledge. This year the meeting also addressed science policy issues, with panel discussions on the „Role of Science in the American Democracy: Roots, Tensions, and Paths Forward” and „European Science Policy Issues on the Move.”
„The clear goal of the various symposiums and panel discussions is to illustrate to scientists who are working in other fields, as well as to members of the press, the progress and the beautiful work that has been done. Some of these talks were just wonderful,” says ITER Deputy Director-General Rich Hawryluk who participated in the symposium on „Worldwide Progress Toward Fusion Energy” and gave a talk on "ITER: A Magnetically Confined Burning Plasma,” completing his presentation with examples of fusion power production and alpha-particle physics studies at JET and TFTR, and stressing how ITER will dramatically extend these results.
ITER was also prominently featured in „Advances in Burning Plasma-Related Physics and Technology in Magnetic Fusion” by MIT’s Amanda Hubbard. A Fellow of the American Physical Society presently working on the Alcator C-Mod tokamak, Hubbard stated that ITER is a priority for the international fusion program, which has focused attention on the critical issues for fusion-scale plasmas. She described progress in simulations of core turbulence and transport, validated by detailed measurements, predictions of the edge transport barrier, and the development of means to control or avoid large edge instabilities.
The final two talks in the symposium were focused on steps beyond ITER. Hutch Neilson from PPPL gave a talk entitled "Issues and Paths to Magnetic Confinement Fusion Energy,” stressing that a new phase of magnetic fusion R&D has now begun. While the success of ITER is the first imperative, nations are already planning roadmaps to DEMO, moving ahead on DEMO R&D, and planning integrated fusion nuclear facilities. There are multiple approaches to fusion development but broad agreement exists on the goals, critical tasks, and the value of international collaboration.
The symposium also addressed the progress accomplished in inertial fusion, with presentations on the National Ignition Facility and the path to laser inertial fusion energy, and on alternate approaches for laser inertial confinement fusion. Mike Dunne, from LLNL updated the audience on the design study of the next-step inertial fusion device LIFE.
Although the AAAS meeting addresses a science-educated public, „most, if not all speakers in other areas of science that I am less familiar with made efforts to be accessible, and they did a very good job,” says Rich. „I learned a great deal from the other talks about the importance and impact of clearly communicating the importance and beauty of the work.”
ITER represents a huge step towards the realization of fusion energy. But even once ITER has achieved the expected plasma performance, a lot remains to be done before we have electricity on our grid generated by fusion.
Fusion researchers around the world are starting to seriously consider the next major step after ITER, known as DEMO, which should be a DEMOnstration power plant, producing electrical power and paving the way for the commercially viable fusion power stations that will follow.
Many conceptual ideas for DEMO designs have been produced over the years, but now that ITER construction is well under way, real proposals for DEMO are being planned.
Unlike ITER, most work on DEMO has been done without much international collaboration although Europe and Japan are cooperating on DEMO design work as part of the „Broader Approach”. But to promote more international sharing of work on the path towards DEMO, the International Atomic Energy Agency (IAEA) arranged a DEMO Programme Workshop that was held at the University of California, Los Angeles, on 15 — 19 October. Over 60 attendees came from fusion research institutes worldwide, including all the countries that are members of ITER.
The workshop was organized around technical topics which are seen as major issues that must be addressed before DEMO can be realized: power extraction, tritium breeding, plasma exhaust, and magnetic configurations. There were also general talks presenting the status of programmes towards DEMO in some of the countries represented.
There are striking differences between the ideas for the plant in the views from different countries. Concepts include tokamaks of various sizes and with varying degrees of advancement from the technology and physics of ITER.
But DEMO could also be a stellarator, or even a „hybrid” that combines fusion and fission in a single device. Some believe that an intermediate step, sometimes called a "Fusion Nuclear Science Facility" or "Component Test Facility", is needed between ITER and DEMO. Such installations would be used to develop and test systems such as breeding blankets, to supplement the work to be done using Test Blanket Systems in ITER. Others prefer to aim for a „near-term” DEMO that would begin by testing its own components.
In all cases, significant materials development is needed, as DEMO will certainly need more advanced structural materials than those being used in ITER. According to some opinions, the planned IFMIF facility will only partly provided the materials tests needed.
With so many diverse ideas, it is not surprising that international collaboration has been scarce. However the workshop did show that there are plenty of common areas in the R&D that needs to be performed, and IAEA will encourage collaboration over these.
Nearly 1,000 of the world’s preeminent fusion researchers from 45 countries gathered last week in San Diego to discuss the latest advances in fusion energy. The 24th International Atomic Energy Agency Fusion Energy Conference, organized by the IAEA in cooperation with the U.S. Department of Energy (DoE) and General Atomics, aims to "provide a forum for the discussion of key physics and technology issues as well as innovative concepts of direct relevance to fusion as a source of nuclear energy.”
Those in attendance in San Diego included Nobel Prize-winning physicist Burton Richter, Physicist Steven Cowley, CEO of the United Kingdom’s Atomic Energy Authority; Frances Chen, a plasma physicist and UCLA professor emeritus who wrote the book „An Indispensable Truth: How Fusion Power Can Save the Planet”, and keynote speaker William Brinkman, Director of the Office of Science in the U.S. DoE.
ITER Director-General Motojima gave the overview talk in the opening scientific session on Monday 8 October and ITER played centre stage throughout the conference, with more than 20 members of staff present providing as many scientific papers and posters (the ITER Domestic Agencies, for their part, contributed 54 papers to the conference).
While acknowledging the difficulties in the implementation of the project which the ITER Organization and Domestic Agencies are tackling, delegates to the conference welcomed the significant technical progress in ITER design and construction activities which were reported in the ITER presentations.
At a "Town Meeting" on the prospects for Burning Plasma Studies at ITER that was, arranged by the local organizers of the conference, presentations by Rich Hawryluk and David Campbell were particularly well received.
Overall, the atmosphere was highly supportive of the ITER project and a substantial fraction of the presentations made at the conference were linked in one way or another to addressing ITER’s R&D priorities.
Significant progress was reported in areas such as the use of all-metal plasma facing components and the associated plasma-wall interaction issues, disruption mitigation, ELM control, H-mode access and confinement. Plans presented for future R&D activities in the major fusion facilities continued to reflect a close link to physics areas which are key to ITER’s success.
Click here to view the conference coverage on KUSI local news channel.
In the pre-2001 design, when ITER was to be nearly the size of Saint-Peter’s Basilica in Rome, 16 cryopumps were to be accommodated at the divertor level of the vacuum vessel.
Cryopumps have the essential function of removing impurities and helium ash from the plasma, enabling the plasma to continue to burn and produce fusion power.
The requirements for vacuum pumping are linked to the plasma fuelling rates—even in the „smaller” ITER these had to be maintained. Design developments in cryo-pumping allowed the machine to be optimized with ten cryopumps in 2001 and eight in 2003.
Eight cryopumps has been the Baseline design figure until recently, when the ITER Director-General proposed to simplify the divertor ports of the machine and remove all „T-shaped” branch ducts. This left only five or six positions where cryopumps could be placed.
This bold proposal was quite a challenge for the ITER Vacuum team. „Let’s say our creativity was strongly stimulated…” recounts ITER Vacuum Section Head, Robert Pearce. „A five-pump solution was proposed, but this was considered rather risky for the goals of achieving ITER’s fusion power mission.”
Following discussions at the Science and Technology Advisory Council in November 2011 and at the Ninth ITER Council later that month, a much improved solution was found: there would be six divertor cryopumps in ITER doing the job that was originally assigned to sixteen.
„Basically, improvements in the cryopumping system design over many years have allowed the cryopumps to sit in bigger housings, enabling them to pump longer and store more gas and impurities,” says Robert. The new housings are „simpler” and have a volume of greater than 14 m3, as compared to 8 m3 in 2003. As the pumping configuration at the bottom of the machine (divertor level) was changed, it became possible to make improvements that resulted in the easier integration of other systems.
„We think that the overall six-pump solution is better in the end: we now have six identical systems. Operations are made simpler and the performance of the system is as good previously,not affected,” conclude Robert and his Vacuum team.
Considering that each branch duct and cryopump is a multimillion-euro component, the savings for the ITER project are considerable.
New images from the MAST device at Culham Centre for Fusion Energy could find a solution to one of the biggest plasma physics problems standing in the way of the development of fusion power.
MAST, the Mega Amp Spherical Tokamak, is the first experiment to observe finger-like lobe structures emanating from the bottom of the hot plasma inside the tokamak’s magnetic chamber. The information is being used to tackle a harmful plasma instability known as the edge localized mode, which has the potential to damage components in future fusion machines, including the key next-step ITER device.
Edge localized modes (ELMs) expel bursts of energy and particles from the plasma. Akin to solar flares on the edge of the Sun, ELMs happen during high-performance mode of operation (’H-mode'), in which energy is retained more effectively, but pressure builds up at the plasma’s edge. When the pressure rises, an ELM occurs—ejecting a jet of hot material. As the energy released by these events strike material surfaces, they cause erosion which could have a serious impact on the lifetime of plasma-facing materials.
One way of tackling the problem is ELM mitigation—controlling the instabilities at a manageable level to limit the amount of harm they can do. MAST is using a mitigation technique called resonant magnetic perturbation; applying small magnetic fields around the tokamak to punch holes in the plasma edge and release the pressure in a measured way. This technique has been successful in curbing ELMs on several tokamaks.
The lobe structures that have recently been observed in MAST are caused by the resonant magnetic perturbation, which shakes the plasma and throws particles off course as they move around the magnetic field lines in the plasma, changing their route and destination. Some particles end up outside the field lines, forming finger-like offshoots near the base of the plasma. Changing the shape of a small area of the plasma in this way lowers the pressure threshold at which ELMs are triggered. This should therefore allow researchers to produce a stream of smaller, less powerful ELMs that will not damage the tokamak.
First predicted by US researcher Todd Evans in 2004, the lobes—known as homoclinic tangles—were seen for the first time during experiments at MAST in December 2011, thanks to the UK tokamak’s excellent high-speed cameras. CCFE scientist Dr Andrew Kirk, who leads ELM studies on MAST, said: „This could be an important discovery for tackling the ELM problem, which is one of the biggest concerns for physicists at ITER. The aim for ITER is to remove ELMs completely, but it is useful to have back-up strategies which mitigate them instead. The lobes we have identified at MAST point towards a promising way of doing this.”
The lobes are significant for another reason; they are a good indicator of how well the resonant magnetic perturbation is working: „The length of the lobes is determined by the amount of magnetic perturbation the plasma is seeing,” explains Dr Kirk. „So the longer the 'fingers,' the deeper the penetration. If the fingers are too long, we can see that it has gone too far in and will start to disturb the core, which is what we want to avoid.”
The next phase of the research will involve developing codes to map how particles will be deposited and how the lobes will be formed around the plasma.
„We already have codes that can determine the location of the fingers but we cannot predict their length due to uncertainties in how the plasma reacts to the applied perturbations. Our measurements will allow us to validate which models correctly take this plasma response into account,” said Dr Kirk. „New codes will mean we can produce accurate predictions for ITER and help them tame the ELM."
Click here for the pdf of this press release.
From May 21-25, a very successful Plasma-Surface Interactions (PSI) conference was held in the historic city of Aachen, Germany, which houses Roman baths and is known as „The Emperor’s City” due to its status as Charlemagne’s favourite place of residence.
The conference, which is held every two years, focuses on the region of the fusion plasma that is closest to the inner wall of the containment vessel, exploring both how the wall is affected and how the plasma responds to the release of wall material. Approximately 400 people came from all of the ITER Member countries, with the number of participants quadrupling since 1980, reflecting the importance of plasma-surface effects in high-performance devices like ITER and fusion power stations.
ITER is considering changing the wall material from carbon to tungsten for the areas that receive the highest heat loads. The conference was very timely in that many of the presentations discussed the properties of tungsten, from melting and gas trapping to less familiar effects caused by plasma exposure such as the formation of bubbles and nanostructures on the surface.
Of particular note was the presentation of initial experimental results from the ITER-like wall that was recently installed in the JET Tokamak. The wall tiles are made from tungsten and beryllium, and are arranged in a way that is similar to the ITER design. There was quite a bit of good news, including fuel retention levels consistent with the ITER requirements and the production of clean, high performance plasmas.
Other topics covered included heat load control, plasma transport, and computer simulations, as well as a look to the future with respect to advanced wall materials, novel magnetic field designs, and reactor requirements.
The final presentation was a lively retrospective by Volker Philipps from Forschungszentrum Jülich that celebrated the 40-year history of the conference and highlighted progress that has been made in the field. The conference location moves between North America, Europe, and Asia; Kanazawa, Japan was announced as the next host city.
The conference’s official press release can be found here.