The ITER Tokamak ultimately will rely on three external heating systems to bring the plasma up to full power: ion cyclotron heating, electron cyclotron heating and neutral beam heating. The US is responsible for both the ion and electron cyclotron heating system transmission lines. For the ion cyclotron system, the European Union will provide two antennas, while India is responsible for the RF power sources and high voltage supplies. The US ITER ion cyclotron team at Oak Ridge National Laboratory has achieved high RF power levels in the laboratory and is working to finalize the design of the transmission lines and matching systems. "We're trying to deliver every bit of power through our transmission lines that we said we would. They are designed to reliably carry double the initially available power, in order to accommodate a possible future power upgrade; we really need to deliver," said Rick Goulding, who leads US ITER's ion cyclotron heating (ICH) research and development program and is a physicist with ORNL's Plasma Technology and Applications Group in the Fusion Materials for Nuclear Systems Division.
US ITER developed a multi-function high power test stand at ORNL to confirm transmission line design and test specific components. Recent accomplishments include successful steady state high-voltage tests of candidate transmission lines at 35 kV, with 40 kV transient currents. The team also successfully tested cooling the inner conductors of the line with circulating nitrogen at 3 atmospheres of pressure. Because of the high power requirements, the diameter of the ITER transmission lines is exceptionally large - about 12 inches - compared with low power transmission lines, such as those used for cable television transmission. In addition to testing performance, the ICH team, which includes staff from both ORNL and Princeton Plasma Physics Laboratory, needs to plan for how the transmission lines will be assembled in the ITER facility. To simplify assembly, the team developed a conductor support design that uses quartz spokes instead of a solid quartz disk. "The advantage of the spoke design is that it can be pre-assembled before being joined to neighboring sections. The design also does not impede the flow of gas, so less pumping power would be required, and the spokes will absorb less RF power, leading to improved efficiency," Goulding said.
Upcoming testing will assess more complicated devices, such as switches and power splitters. In addition to the resonant line, which creates a standing wave to achieve the highest possible voltage, a resonant ring has been built that distributes power more evenly along the test line - closely mimicking the heating that occurs in the bulk of the ITER transmission line. The resonant ring can be routinely operated at 6 megawatts for an hour; 17 long-pulse tests have been completed on the ring since 2012. As different prototype components are assessed, the ICH team has refined the test stand and its software controls to enable efficient, consistent, accurate testing. "The transmission lines are expected to be the highest reliability components in the ion cyclotron system," Goulding said. Once the transmission lines are installed in the ITER facility, they will operate for many years.
Blanket First Wall Panels
The first of a series of steps to qualify the fabrication of the ITER blanket's first wall panels has been achieved in Europe, with the successful manufacturing of a semi-prototype. The completion of the 1:6-scale model moves the European Domestic Agency a step closer to obtaining qualification for series production. The panels are 1 x 1.5 metre detachable elements which, together with the shield block, form the ITER blanket modules. Designed to withstand the heat flux from the plasma, the first wall panels are high-tech components made of beryllium tiles that are bonded with a copper alloy and 316L (N) stainless steel. Europe is responsible for procuring the normal heat flux first wall panels (about half of the 440 panels required for the blanket); China and Russia are sharing the procurement of enhanced heat flux panels that make up the other half.
The semi-prototype will now be subjected to an electron beam capable of applying the same heat flux the panels will experience in the ITER machine, bringing the surface temperature of the beryllium to approximately 400°C. The European Domestic Agency has awarded the grant for high heat flux testing to the German research centre Forschungszentrum Jülich, which expects to complete the campaign this summer. A Procurement Arrangement is scheduled to be signed with the ITER Organization in early 2015 for the procurement of Europe's portion of the first wall panels.
Test Blanket Module Program
The eleventh meeting of the ITER Council Test Blanket Module (TBM) Program Committee took place on 21-23 of May in the Council Chamber of ITER Headquarters. The TBM Program Committee meets twice a year to review the implementation of the TBM program, including the ITER Members' Test Blanket Program and the ITER Organization's TBM integration activities. Typical standing items at each meeting include the status of the TBM-related activities within the ITER Organization, TBM design and R&D progress within the ITER Members, and the status of corresponding milestones. During the eleventh meeting, good progress was reported by the TBM Leaders, who hold the responsibility for specific Test Blanket Systems. Design development is progressing in view of upcoming conceptual design reviews for each system, and design activities under ITER Organization responsibility - for TBM port cell components and specific maintenance tools and equipment - are advancing.
The first component delivery associated with the TBM Program is expected in 2017 and will concern Test Blanket System connection pipes, which will connect the components located in the TBM equatorial port cell to the components located in other rooms of the Tokamak Complex via the corresponding shaft and/or corridor. With the conceptual design review planned for September 2014, the eleventh TBM Program Committee assessed the readiness of the design.
The Committee also took note of the status of the activities of the Test Blanket Program Working Group on Radwaste Management. This working group is charged with the elaboration of a potential strategy for the management of TBS radwaste and for the shipping of irradiated TBMs to Members' facilities for post-irradiation examinations. The TBM Program Committee has assessed the data on radwaste furnished by the ITER Members and on the radwaste management proposals of Agence Iter France. One of the major issues identified to date is the need for an assessment of the amount of tritium remaining in the waste and of the corresponding outgassing. In fact the year 2014, with the planned conceptual design reviews of five Test Blanket Systems out of six, represents the beginning of a new phase for the TBM Program, which is passing from pure scientific research to nuclear engineering and realization. This aspect was stressed by the TBM Program Committee as it focused the discussion on the preparation of documentation for the various conceptual design reviews.
Neutral Beam Test Facility
In the industrial outskirts of Padua, Italy, about 40 kilometres west of Venice, the long white buildings of the PRIMA Neutral Beam Test Facility are now ready to receive equipment, after a little over a year of construction activity. At PRIMA, the components of ITER's most powerful heating system - neutral beam injection - will be tested in advance of ITER operation. Europe, Japan and India are contributing all components according to the specifications of Procurement Arrangements signed with the ITER Organization; Italy is building the facility as a voluntary contribution to the neutral beam development program. The PRIMA facility is hosted by Consorzio RFX, an Italian research laboratory for plasma physics and controlled nuclear fusion. Two test beds at PRIMA will help resolve challenging physics and technology issues and validate concepts before the neutral beam system is built at ITER. The first, SPIDER, will operate an ITER-scale radio-frequency negative ion source. After approximately two years from the start of SPIDER, a second facility, MITICA, will enter operation to test the 1:1-scale neutral beam injector at full acceleration voltage and power.
Fabrication is now underway for all SPIDER components. Factory acceptance tests on the vacuum vessel are planned mid-year in Europe; delivery of the 100 kV power supply and beam dump (part of the Indian contribution) is expected at the end of year according to plan. For MITICA, all of the build-to-print mechanical components have reached the final design stage and were presented for review in January 2014. Following chit resolution, procurement of these components will be launched by the European Domestic Agency. All of the components for the PRIMA test beds belong to the ITER Organization. Once they've been delivered to the site in Padua and have passed acceptance tests, ownership responsibility will be transferred to the European Domestic Agency for the duration of SPIDER and MITICA operation.
Divertor Remote Handling System
The long concept preparation phase for ITER's high-tech divertor remote handling system has come to an end and industry is about to take over, thanks to a seven year, multimillion-euro contact signed between the European Domestic Agency for ITER and Assystem, a leading consultancy firm in engineering and innovation. Assystem and its partners will have the responsibility for the design, manufacture, delivery, installation, commissioning and final acceptance tests of the remote handling systems that will be charged with the remote replacement of ITER's 54 divertor cassettes. Running toroidally along the bottom of the vacuum vessel the ITER Divertor acts as the Tokamak's exhaust system, extracting helium ash from the burning plasma. Due to the tremendous heat loads and magnetic forces that divertor components will face, replacement is planned three times over the course of the machine's lifetime.
Sample Toroidal Magnet Conductor
The US Domestic Agency US ITER worked closely with vendor High Performance Magnetics in Tallahassee, Florida, to complete fabrication and transfer 800 metres of sample toroidal field magnet conductor to the port in Charleston, South Carolina, from where it will be shipped to the European winding facility in Italy. Delivery was expected to occur in late June. The shipping procedures are exacting to ensure the safe delivery of the sample conductor, which weighs about 14,000 kilos - shipping crate included. "The coil of sample conductor is about four metres in diameter. It is stacked up like a slinky and can actually move like a Slinky if we don't secure it," said Kevin Chan, a project engineer for the US ITER magnet systems.
The sample conductor, composed of non-superconducting copper strands, was produced in order to qualify the conductor fabrication processes; the production conductor installed in the ITER Tokamak will be composed of a mixture of copper and niobium-tin superconducting strands.
"There are a lot of unique aspects to ITER shipments, including international collaboration, dealing with a variety of shipping origins and destinations, different vessel types and selecting the best method for transportation with attention to costs, timing and risk," said Jeff Parrott, logistics and transportation coordinator at US ITER.
Magnet Feeder Vacuum Vessel
The Chinese Institute of Plasma Physics (ASIPP) has successfully accomplished a full-scale qualification prototype for one of the key components of ITER's magnet feeder system - the vacuum vessel that will provide thermal insulation to the components at the very end of the feeders inside of the Tokamak gallery. The ITER superconducting magnet system consists of 18 toroidal field coils, 6 poloidal field coils, a central solenoid (6 modules), 18 correction coils, and finally a coil supporting structure. Leading away from the magnets, 31 superconducting magnet feeders will provide connections to the power supplies, the cryogenic plant, and the magnet control and safety units. Each feeder is made up of an in-cryostat feeder, a cryostat feed-through, and the coil terminal box/S-bend box (CTB/SBB) assembly. At the end of the feeders, within the Tokamak gallery, are the critical CTB/SBB boxes where electrical power and cryogens are relayed through the warm-cold barrier of the cryostat to ITER's powerful magnets that operate at currents from 10 kA to 68 kA.
A protective vacuum vessel will provide thermal insulation for hundreds of encapsulated cryogenic components that are part of the boxes such as a 80K thermal shield,high temperature superconducting current leads, superconducting busbars, cryogenic coolant circuits with control/safety valves, cold sensors and signal cables, and cold mechanical supports (see diagram). The CTB/SBB vacuum vessel is thus the largest (8m x 1.3m x 1.5m) and heaviest (18 t) feeder component. The final weight of a fully loaded CTB/SBB, vacuum vessel included, is 27 tons.
In order to meet ITER's stringent quality requirements, the Chinese manufacturer conducted a series of welding trials and assessments and submitted as many as 82 quality documents to the ITER Organization. A number of experts and certified third-party inspectors were invited by the ITER Organization to witness different stages of key welding processes as well as vacuum leak checking, non-destructive testing, and large component measurements. The successful realization of the full-scale qualification CTB/SBB vacuum vessel prototype is a significant accomplishment. The experience gained in this prototype qualification has laid a solid foundation for the high quality series production ahead. The qualified component will now be used at ASIPP to provide the necessary vacuum environment for the downstream cryogenic qualification tests of the 80K thermal shield and the high temperature superconducting current lead prototypes, as well as the full-size mockups of the S-bend busbars with high voltage insulation.
DC Busbars
In early June at the Efremov Institute of Electrophysical Apparatus (Saint Petersburg, Russia) specialists completed type tests on full-scale prototypes of the DC busbars (10 to 68 kА) - the sizeable, water-cooled components will feed power to ITER's superconducting magnet coils. The series of tests carried out at the Institute were attended by experts from the ITER Organization and ITER Russia.
The high-current busbars that connect tokamak coils with their power supplies, as well as thyristor converters and powerful switching devices and resistors for the extraction of energy from the magnet system, compose the core part of the electrotechnical equipment to be manufactured and delivered by Russia according to the Procurement Arrangement signed between the ITER Organization and ITER Russia in 2011. Almost all of the equipment is one of a kind and was specially designed for the ITER Project. The Efremov Institute has the responsibility for designing, manufacturing and testing of all the equipment. The tests carried out in Saint Petersburg this spring included a broad array of electric, hydraulic and mechanical tests of the busbars elements that aimed to verify that their parameters matched technical specifications. The tests results confirmed the technical solutions conceived during the design stage, including manufacturing technology. The positive test results now give the green light to the busbar serial production. According to the terms of the Procurement Arrangement, the Efremov Institute will manufacture and ship to the ITER Organization over several years about 5.4 km of busbars with a total weight exceeding 500 tons
For further information on ITER progress, visit http://www.iter.org