First design review within Test Blanket Module program

Last week the ITER project—and the worldwide fusion community—celebrated yet another premiere: the first conceptual design review within the Test Blanket Module (TBM) program, a key technology development paving the way to fusion power. It was not yet the turn of the tritium-breeding test modules to be assessed, but that of the components required for hosting them.
During its operational phase, ITER will draw upon the global (civil) inventory of tritium, currently estimated at 20 kilos.

But future fusion power stations would have to create their own supply of tritium. Part of ITER’s mission is to test different tritium breeding concepts proposed and developed by the Members … concepts that will enable future fusion reactors to produce their fuel within the machine (tritium self-sufficiency) and at the same time extract the heat produced by the fusion reaction and convert it into electricity.

While six different tritium breeding concepts—the Test Blanket Modules—are currently in their pre-conceptual design phase, a group of experts lead by ITER Senior Engineer Guenter Janeschitz last week concluded the first design check of the modules’ frames and housings, as well as the dummy modules that will be needed to substitute for the actual TBM sets in order to close and seal the port plugs in the case of delayed delivery or in case replacement is required. Mario Merola, in charge of ITER’s in-vessel components, called the design review „a significant step forward toward the goal of testing tritium breeding technology.”

The current strategy foresees that the dummy TBM sets and the frames shall be made of water-cooled 316-L(N) steel (ITER grade), a special metal that guarantees reduced activation when exposed to neutrons, no ferromagnetic effects and adequate mechanical properties. To reduce maintenance time, the replacement of a TBM will be performed „off-line,” meaning that the entire port plug (with its TBM sets, plus frame) will be removed, stored in the Hot Cell, and replaced by a new plug with a new set of equipment. Delivery and installation of the six Test Blanket Systems is planned during the machine’s first shutdown period following First Plasma.

„We looked at the design concept from all possible different angles and the requirements have been clearly identified,” the Chairman Guenter Janeschitz stated in the panel’s close-out session, praising the high level of preparation of the review. „A significant effort was made in the presentations to cover, in a quite comprehensive manner, systems requirements, design analysis, interface requirements and manufacturing aspects—therefore, the objectives of the design review were achieved. However, a few issues such as the potential contamination of the port flange, the still-insufficient shielding performance, the attachment of the TBM sets or their dummies to the frame structure, and the expected thermal stresses these components could be exposed will have to be further considered during the post-conceptual design phase.”

The fellowship of the Plasma Ring

Thirty years ago, on 25 June 1983, the Joint European Torus (JET) came to life with a flash of plasma. „There was an air of hushed expectancy as the countdown for the first plasma attempt progressed,” remembers Phil Morgan, then an optical spectroscopy specialist who had joined the project the year before. „A suppressed gasp was heard as on one of the TV screens the machine appeared to tilt when the magnetic field was switched on—then loud laughter as people realized that the field was distorting the image recorded by the TV camera.”

This anecdote and many others were shared on 24-25 June as JET and ITER personnel, connected by video link, assembled to commemorate the event that, 30 years ago, opened a new era in the history of fusion.

In the ITER Council Room, where some 25 former members of JET’s staff had gathered around the head of ITER’s CODAC, Heating & Diagnostics Directorate, Paul Thomas, and at Culham, where participants were hosted under a tent, participants remembered with equal emotion the intensity of the peak plasma current that was achieved on that day and the taste of the minestrone soup prepared by the wife of Franco Bombi, then head of JET’s Control and Data Acquisition System.

To Paul, and many others who now are part of the ITER team, JET provided „invaluable experience.” Thirty years after its first plasma and two decades after its first burst of fusion power on 9 November 1991, „JET is the key device to resolve many of the challenges that we are facing,” (Mike Walsh, head of Diagnostics); „Its input is critical for our commissioning plan,” (Ken Blackler, head of Assembly & Operations); „It continues to deliver important results that provide direct input, even today, in our design decisions,” (Günther Janeschitz, Engineering Officer).

The posters decorating the conference room at Culham for this two-day celebration read: „30 years of JET — Paving the way to ITER’s take-off.” ITER Director of Plasma Operation David Campbell, who made the trip to JET, stressed this important mission in his speech, broadcast live: „JET provides substantial training for those who will operate ITER.”

More coverage on the EFDA website.

Lawson’s magic formula

In 1955 a young engineer working on nuclear fusion decided to work out exactly how enormous the task of achieving fusion is. Although his colleagues were optimistic about their prospects, he wanted to prove it to himself. His name was John Lawson, and his findings—that the conditions for fusion power relied on three vital quantities—became the landmark Lawson Criteria.

The genesis of Lawson’s Criteria is simple enough—he calculated the requirements for more energy to be created than is put in, and came up with a dependence on three quantities: temperature (T), density (n) and confinement time (τ)*. With only small evolution thanks to some subtle changes of definition, this is basically the same figure of merit used by today’s fusion scientists, the triple product, nτT.

The amount of energy created relies on particles colliding and fusing—the number of collisions is related to the number of particles in a certain region—thus n, the number density (not mass density) is Lawson’s first criterion. This would seem encouraging for the prospective experiment, as creating high pressure is relatively easy. However there is a catch. At higher densities a process known as bremsstrahlung rears its ugly head, in which collisions between nuclei and electrons generate radiation. Bremsstrahlung can become so dominant that all the power in the plasma is radiated away; the optimum density conditions are surprisingly low, around a million times less dense than air.

Nonetheless the fusion collisions—between the nuclei—have to be at high speed. This allows the nuclei to overcome their electrostatic repulsion, and get close enough for the strong force that governs fusion to take over and stick the particles together. The speed of a gas or plasma particle is equivalent to its temperature: the second of Lawson’s criteria.

Again there is a limit—if the two particles are moving really fast then the time they are in close enough proximity for fusion to occur decreases. The bremsstrahlung also increases at higher temperatures, due to faster moving electrons. The Goldilocks temperature turns out to be in the vicinity of 100—200 million degrees, a seemingly huge task in the fifties that has become a standard condition today.

* "τ" is the Greek letter tau (pronounced like "how").

Read more on the EFDA website.

AAAS: the beauty of Science

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.”

DEMO: time for real proposals

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.

1,000 researchers, 400 reports on fusion progress

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.

Cryopumps: fewer, cheaper and no less efficient

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.

Plasma fingers point to the taming of the ELM

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.

Positive results with new wall materials at PSI 2012

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.