Galeria

Oak Ridge National Laboratory's Fusion Pellet Fueling Lab has been at the center of design and testing of plasma fueling systems for tokamak research applications for decades. Since the mid-1970s, lab researchers have been designing, testing and contributing hardware for fusion magnetic confinement experiments here in the United States and around the world. As the US ITER project moves from design and testing of components to manufacturing, the lab is making prototypes for the ITER tokamak. ITER's "first plasma" is planned for around the close of this decade.

ORNL researchers David Rasmussen, Steve Combs, Steve Meitner, Larry Baylor, Charles Foust, Dan Fehling, James McGill, John Caughman and Robert Duckworth are among the key players involved in testing pellet injector technology for fueling and for controlling the plasma. The technology then goes to plasma experiments for testing in tokamaks in real-time fueling environments.

The lab's efforts include work for the JET (Joint European Torus) tokamak in the United Kingdom, currently the largest fusion experiment in the world; for the DIII-D tokamak operated for the US DOE by General Atomics in San Diego; and in the past, for collaborations with France's Tore Supra and Japan's Large Helical Device (LHD). When ITER is built in France, it will have a plasma volume that is two times larger than the capacity of any current tokamak.

Current research continues on the following areas which are important for US ITER contributions to fueling, disruption mitigation, and vacuum systems:

Pellet Injectors. "The initial plan for ITER is to have two injectors," says Steve Combs, a chemical engineer who has spent much of his career in the ORNL Fusion Energy Division developing pellet injectors and related technologies. One of the ITER pellet injectors is for fueling, using ~5.3 mm pellets; the other is for controlling the density at the edge of the plasma boundary by injecting relatively small pellets to produce small edge localized modes, or ELMs. Pellets for ELM pacing will be roughly 3 mm in size. "Large ELMs can damage the plasma facing materials in the divertor, so we must inject pellets at fairly high frequency," says Combs. To better understand the potential of ELM pacing, an ORNL pellet injection system on DIII-D is being modified to inject relatively small deuterium pellets at 40-50 Hz; initial testing is planned for later this year. Pellet systems are also being designed and tested for plasma disruption mitigation. Large pellets, greater than the size of wine corks, and multiple injection sites are being considered for reducing the impact of plasma disruptions in ITER. Such a system is already installed on the DIII-D tokamak and has been successfully used in experiments, with more planned this year.

Massive Gas Injection Technology. An alternative massive gas injection system for plasma disruption mitigation has also been developed. Comparing results from this system with those from massive pellet systems will help researchers determine the best disruption mitigation design for ITER. The advantage of using gas is that it is conceptually a very simple system. However, maintenance would be problematic in the case of mechanical problems or any leakage from a close-coupled valve, since the gas valve must be located close to the tokamak to be effective. "At this moment it is not obvious what would comprise the optimal system," Combs says. "Several groups around the world are looking at it. It has some high priority now for ITER."

Microwave Cavity Mass Detector. A prototype diagnostic to measure the pellet mass in flight has been tested in the ORNL fusion pellet fueling lab. The microwave cavity mass detector is currently the main diagnostic for recording real-time pellet mass, size, and speed. "This will tell the physicists how many particles are injected into the plasma at a given time," Combs says. The detector measures the mass of each pellet emerging from the injector as it passes through a tuned resonant cavity that is optimized for performance at a specific frequency. As the pellet passes through the cavity, the cavity is detuned, producing an electrical signal that is proportional to its mass; the detector data also provide the pellet speed. Two detectors will be included downstream of the injector barrel on the ITER injectors. "The two prototype microwave cavities in the lab need some minor changes to be completely compatible with the tritium environment for ITER," Combs says. "They look pretty good. They are essentially prototypes for ITER."

Cryogenic Viscous Compressor (CVC). The ITER vacuum system requires a roughing pump system that can pump the exhaust gas from the torus cryopumps to the tokamak exhaust processing plant. The gas will have a high tritium content and conventional vacuum pumps are not suitable for handling this radioactive isotope. A pump called a CVC is being designed for the ITER roughing system to pump from ~500 Pa to 10 Pa at flow rates of 200 Pa-m3/s. A unique feature of this pump is that it allows any helium in the gas to flow through the pump, where it is exhausted to the atmosphere. In the fusion pellet fueling lab, a small-scale prototype of the CVC is now being tested for heat transfer characteristics and compared to modeling results, to ensure reliable operation of the full-scale CVC. This research is being conducted under the direction of Mike Hechler, the vacuum pumping lead for US ITER. "We are helping the vacuum team with this," says Combs. Nothing now exists anywhere in the world that will do this. They are getting ready to build a full-scale prototype module soon. If that works out well, they will then begin to design the final units for ITER.

"All these projects use common equipment here in the fusion pellet fueling lab, to save money," notes Combs. "One day we run one or two experiments, and on another day, we run one or two other experiments. We work together as a team, and things work out just fine. We look forward to our components/systems being used in ITER. We have a real sense of pride in it. In the next five to six years, we have to get some real systems ready forITER. We have to test them, and then we have to deliver reliable systems."

Provided by Oak Ridge National Laboratory (news : web)

Source: physorg.com

The Council of the European Union agreed to extend for more two years (2012 - 2013) the current Euratom framework programme for nuclear research, which expired in the year 2011.

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The EU has agreed to fund ITER €1.3 billion($1.7 billion) through 2013. ITER is an international project that plans to construct a superconducting fusion reactor in Cadarache, France, by 2019. The agreement still has to be formally adopted by ITER and the EU.

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Good progress is now being made with JET's additional heating systems. The ICRH system is working routinely, and significant amounts of power are also being injected using the Neutral Beam Injection systems.

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2011 has been the year that fundamentally transformed the ITER construction site in Cadarache. The designs of two key buildings have come to life and demonstrated even to sceptics that the collective commitment and determination of the ITER parties has paid off.

It’s one of the last dawns of the year and we have decided to visit the ITER platform, located at one the highest points of the site, so as to observe the scale of progress. The activity is kicking off as the workforce resumes its tasks, the site is getting noisier and busier with trucks, cranes start moving materials and the first buildings stand out in what was until a year ago a field. So how did we get here?

F4E, managing Europe’s contribution to ITER, is responsible for the financing and supervision of the construction of buildings, infrastructure and power supplies. A sequence of events starting with internal co-ordination for the drafting of specifications, the launch of procurement packages linked to the work on the site, awareness days with industry and SMEs, the signature of contracts, the deployment of resources on the site and steady supervision of contractors make up to the work behind the scenes.

After months of intense construction work the Poloidal Field Coils (PF) building is nearly completed. Its impressive dimensions: 250 metres long, 45 metres wide and 17 metres high are vivid reminder of the size of the coils that will be assembled here for the ITER machine. The cladding, insulation and the transportation of heavy equipment like the two cranes and the spreader have reached their final destination and have been assembled.

As we cross the site we arrive at the Tokamak complex, the heart of the ITER project. Only one year ago the excavation started with rock blast activities and bulldozers levelling the ground. In spring, what used to be an amorphous pit started transforming into the foundation of the Tokamak complex covered with a steel safety mesh in order to continue with the soil investigation activities and the treatment of rock joints. In summer we reached a breakthrough: the first steel reinforcement and the pouring of the first concrete. Two pumps were placed at the top of the Tokamak pit and for approximately ten hours 800m³ of concrete were poured and leveled. This exercise was to be repeated 21 times in total in order to cover the entire surface of the Tokamak pit measuring 110 metres long and 80 metres wide, the equivalent to the footprint of a football stadium. In autumn, the plinths and anti-seismic bearings started populating the basemat exceeding 250 in total accompanied by the first glimpse of the of the retaining walls foundations.

The transformation of the site is only the beginning of what will follow next year. The signature of the site adaptations contract in August, is expected to deliver the necessary works on the ITER site in order to develop roads for the transport of material and equipment, extend power supply and water distribution, deliver the required amenities for a workforce of 3,000 people and streamline all protocols for safety, security and access to the site.

We will continue to bring you the latest news through images, clips and updates through Twitter and YouTube next year! To watch the two annual clips documenting the PF Coils building and the Tokamak complex progress during 2011 click here.

Source: F4E