EAST meets WEST

An Associated Laboratory in fusion was established earlier this month between the Chinese Academy of Sciences (CAS) and the French Commission of Atomic Energy (CEA) to develop cooperation on two long-pulse tokamaks, EAST and Tore Supra, soon to be equipped with an ITER-like tungsten divertor — the project WEST.

The creation agreement was signed on 3 July by Prof Li, director of the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) and Gabriele Fioni, director of CEA’s Physics Science Division, CEA, at the French Embassy in Beijing. French nuclear counselor Pierre-Yves Cordier hosted the signing ceremony, with André Grosman, deputy director of the Institute of Magnetic Confinement Fusion Research (IRFM/CEA) and consular assistant Shunming Ding. 

The associated laboratory has been created to develop cooperation on CEA’s long-pulse tokamak WEST* and ASIPP’s EAST, particularly in the fields of actively cooled, metallic plasma-facing components; long-duration plasma operation in an actively cooled, metallic environment; long-pulse heating and current drive; ITER technology support; and the preparation of „Generation ITER” (see this issue’s Of Interest entry) in all of the above-mentioned areas.

Xavier Litaudon and Yuntao Song are appointed as the associated laboratory’s co-directors. They will be responsible for leading and coordinating the performance of the projects under the Associated Laboratory Agreement.

„I am enthusiastic about the CAS/ASIPP-CEA collaboration,” said Prof Li after the signature. „The cooperation between EAST and WEST will be good for all fusion communities.”

As a first step, ASIPP has already sent two young researchers to IRFM to work for one year on WEST component design and engineering.

* WEST = W (tungsten) environment for steady state tokamak

Design Review for tungsten divertor shows way ahead



Last week, the ITER Organization concluded the Final Design Review for a full-tungsten ITER divertor. In this three-day assessment, which was the culmination of eighteen months of design, analysis, testing and development, the readiness and the feasibility of a full-tungsten variant capable of withstanding the extreme conditions in ITER were assessed. Challenges related to the specific nature of tungsten were identified and dealt with. „The completed design now requires some refinement with respect to the local shaping of the tungsten monoblocks,” said Philippe Mertens from the Research Centre in Juelich, Germany, who chaired the review.

Almost five years ago, in its 60th issue, the ITER Newsline announced the upcoming Final Design Review of the divertor system. At that moment, the ITER approach was to begin plasma operations with carbon fibre composite (CFC) on the regions of the divertor’s vertical targets that are expected to receive the highest heat loads. All other plasma-facing surfaces would have been armoured with tungsten.

So much for the non-active phases of plasma operation. The ITER approach for the following phase—nuclear operation with deuterium and tritium—was to replace the carbon-tungsten divertor with a full-tungsten variant.

Carbon presented two major drawbacks as divertor armour material: it reacts chemically with the plasma fuel tritium and it traps the fuel like a sponge, leading to enhanced material erosion and unacceptable levels of tritium retention within the machine. Tungsten (W), on the other hand, has the advantage of not absorbing tritium, but at the same time it doesn’t offer the same forgiving behaviour as carbon in terms of compatibility with the plasma.

In September 2011 budget restrictions forced the ITER Organization to reconsider its Baseline divertor strategy. By launching operations with a full-tungsten divertor from day one, one of the three divertors planned for ITER’s 20-year operational phase would be eliminated.

A comprehensive investigation was launched in 2011—the Tungsten Divertor Qualification Program—in consultation with the procuring Domestic Agencies in Russia, Europe and Japan. The program comprised full-scale prototype manufacturing and testing.

While many of the features of the existing CFC/W Baseline design are applicable to a full-tungsten divertor for ITER, there are some key differences. Employing metal in high heat flux areas for example requires particular attention—where carbon was known to have favorable properties for the „plasma machining” of misaligned edges (due to manufacturing and assembly tolerances) these do not to apply for tungsten.

Attention must also be paid to the global shaping of the upper baffle areas of a tungsten divertor, where off-normal events such as a sudden vertical displacement of the plasma are predicted to lead to extremely heavy heat loads. Through the slight tilting of the targets and through particular shaping of the outer baffle (very much like the shaping of the first wall of the blanket) some promising results have been obtained that were presented during the design review.

_To_56_Tx_High heat flux tests performed last year at the newly completed ITER Divertor Test Facility in Russia—with prototypes manufactured by Japanese industry that were exposed to 10 MW/m2 over 5000 cycles and 20 MW/m2 over 1000 cycles—demonstrated no macroscopic cracks, de-bonding or traces of melting. Similar tests run for 300 cycles at 20 MW/m2 have been performed by European industry with optimistic results. 

A „melt experiment” consisting in the deliberate melting of tungsten tiles has been proposed for JET this summer to better understand the behaviour of the molten layer and the consequences of operating a machine on re-solidified W layers.

„It is now expected to report the last findings on this full-tungsten divertor variant to the next ITER Council Science and Technology Advisory Committee (STAC) in October 2013, to obtain a recommendation on the divertor armour for ITER. The objective would be to implement the decision into the Baseline by the end of the year,” said Frederic Escourbiac, leader of the Tungsten Divertor Section, who was clearly satisfied by the outcome of the particularly intense three-day design review.

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.

Discussing experiments and aligning priorities

The 10th Integrated Operation Scenarios (IOS) International Tokamak Physics Activity (ITPA) meeting was held in the ITER Council Chamber from 15-18 April 2013. There were 30 external participants from the ITER Members and a number of representatives from the ITER Organization. The external participants include representatives from the main magnetic fusion devices and modellers from the ITER Members.

The purpose of the meeting was to discuss the experiments and modelling being carried out around the world in support of the ITER design and plasma operation as well as to align the priorities for future R&D with the latest ITER priorities. The IOS Topical Group (TG) is one of seven topical groups in the ITPA whose main role is to integrate plasma operation scenarios for burning plasma experiments, particularly for ITER, including inductive, hybrid, and steady-state scenarios. The IOS-TG also recommends physics guidelines and methodologies for the operation and design of burning plasma experiments. The ITPA topical groups all meet every six months in one of the countries of the ITER Members. This was the first time the IOS-TG met at ITER, allowing the members and experts of the IOS-TG to see first-hand the progress in ITER construction. 

Experimental and modelling results were presented from Alcator C-Mod, ASDEX-Upgrade, DIII-D, JET, JT-60U, and KSTAR of ITER-relevant plasma operational scenarios. Experimental results concentrated on inductive and hybrid scenarios; modelling of steady-state scenarios was also presented. Modelling of burning plasma and energetic particle physics were presented as well as plasma rotation in ITER and their impact on operational scenarios. The predicted plasma rotation profiles in hybrid scenarios were strongly peaked with rotation up to nearly 200 km/s, corresponding to about 4 kHz rotation in ITER in the centre. The effects of the Edge Localized Mode (ELM) coil fields on fast ion losses comparing vacuum fields and the plasma response were also shown, indicating that when the plasma response is included, the fast ion losses are acceptable even at high performance with the maximum ELM coil current.

The IOS-TG also concentrates on plasma control including experiments and modelling of profile control as well as development of the preliminary design of the ITER plasma control system (PCS). A review of the PCS conceptual design was presented as well as an action plan for how the experimental and modelling programs within the ITER Members can contribute to developing the PCS preliminary design for First Plasma and early hydrogen and helium plasma operation. Modelling of control of the entry into a burning plasma regime was also presented. A proposal was made to integrate experiments and modelling of plasma control schemes for ITER in existing experiments so that these control schemes can be developed before ITER operation to reduce run time on ITER for control scheme development. A request was made for the ITPA to provide control priorities for the ITER actuators starting with a few phases of plasma operation. 

As part of the ITPA response to the question of starting ITER with an all-tungsten divertor, the IOS-TG discussed the effect of a tungsten divertor on operational scenarios. Reports from DIII-D, ASDEX Upgrade, and C-Mod compared operation with carbon walls and metal walls. Although there were some differences, it was generally believed that ITER would be able to learn how to operate with beryllium walls and an all tungsten divertor.

Modelling of ITER and JET current ramps were also presented indicating the differences between operation with carbon walls and with the ITER-like wall on JET. Since the peak in radiation for tungsten occurs around a temperature of 1 keV, the radiation from tungsten will be peaked near the edge in ITER. There is still a question about whether or not the tungsten transport into the core can be controlled to a sufficiently small value.
Modelling of steady-state fusion plasma scenarios was also presented to understand how the present heating and current drive systems should perform as well as what upgrades might be required to meet the long-pulse goals of the ITER program. The modelling includes simulation of sawtooth control, kinetic integrated modelling, and parameter scaling from existing experiments to ITER steady-state regimes. An update was also given on the latest proposed changes to the steering of the electron cyclotron heating and current drive system that was followed by extensive discussion.

In summary, the meeting provided valuable information on recent experiments and modelling of ITER plasma operation scenarios. Actions for the ITPA members and experts to help define the preliminary design of the ITER plasma control system were agreed upon. Continued experiments and modelling to demonstrate ITER operational scenarios for the inductive, hybrid, and steady-state scenarios were presented. A special report on the impact of an all-tungsten divertor on ITER operational scenarios was also discussed at length. 

Korea awards contract for ITER thermal shields


The Korean Domestic Agency signed a contract with SFA Engineering Corp. for ITER thermal shields on 28 February. The contract covers the detailed design of manifolds/instrumentation, the manufacturing design and the fabrication of the thermal shield system. „For us, this is a big step forward for the Korean contribution to ITER,” said Myeun Kwon, president of the National Fusion Research Institute, after the signing.

SFA is a leading company in industrial automation with much experience in the procurement of advanced equipment related to fusion, accelerator, and space technology. SFA was deeply involved in the manufacturing and assembly of the Korean tokamak KSTAR.

The ITER thermal shield will be installed between the magnets and the vacuum vessel/cryostat in order to shield the magnets from radiation. The thermal shield consists of stainless steel panels with a low emissivity surface (<0.05) that are actively cooled by helium gas, which flows inside the cooling tube welded on the panel surface. The temperature of helium gas is between 80 K and 100 K during plasma operation. The total surface area of the thermal shield is approximately 4000 m2 and its assembled body (25 m tall) weighs about 900 tons.

The key challenges for thermal shield manufacturing are tight tolerances, precision welding, and the silver coating of the large structure. The thermal shield also has many interfaces with other tokamak components. „The Korean Domestic Agency is satisfied with this contract because the thermal shield is one of the most critical procurement items in the ITER project. We will do our best in collaboration with the ITER Organization to successfully procure the ITER thermal shield,” said Hyeon Gon Lee, DDG of the Korean Domestic Agency, on the occasion of the contract signature.

Romanelli sees JET as "main risk mitigation" for ITER

On the afternoon last year when the European tokamak JET attempted first plasma after an 18-month shutdown, Associate Leader Francesco Romanelli remained in his first-floor office. „I wasn’t expecting the machine to perform so faultlessly on its first attempt,” he later explained. „Besides, things had a way of going wrong when I entered the room, so maybe it was better after all.”

That anecdote and others were related by Romanelli at last week’s Inside ITER seminar, during which he gave a first-hand overview of the ITER-like wall campaign that has been running at JET since that first (very successful) day back in August 2011. Three thousand installable items and 16,000 tiles had been replaced in the machine (non-metal carbon tiles were replaced by the metals beryllium and tungsten) to equip JET with the same materials mix chosen for ITER.

Romanelli reported in detail on the experimental results so far: demonstration of low fuel retention, tungsten divertor successfully tested, observations related to the dynamics of disruptions …

„Overall, the operation of the ITER-like wall has been easier than expected, giving us the confidence that the fusion community is making the right choice for ITER. We see JET as the main risk mitigation measure in support of ITER.”

The European Fusion Development Agreement is already looking ahead to other roles for JET—developing plasma scenarios in ITER-relevant configurations and testing the compatibility of the wall with the use of tritium. „JET can provide unique input in a number of technical and operational areas.”

David Campbell, director of ITER’s Plasma Operation Directorate, agrees: „The crucial ITER-like wall experiment will give us insight—ahead of ITER operation—as to how fusion plasmas will behave in the presence of the plasma-facing mixture that we’re planning to use in ITER.”
For more on JET’s ITER-like wall campaign, visit the EFDA-JET website.

ITPA decides on research priorities for 2013

Last week, a key meeting for the implementation of ITER physics R&D took place in the new Council Chamber. The Joint Meeting of the International Tokamak Physics Activity (ITPA) Coordinating Committee and the International Energy Agency Implementing Agreement (IEA IA) on Co-operation on Tokamak Programmes (CTP) is an annual gathering of senior representatives of the ITER Member fusion communities, the ITPA Topical Group leadership and program leaders from the major fusion facilities.

The 56 participants that had travelled from the ITER Members joined 12 from the ITER Organization for the meeting. In his opening remarks, ITER Director-General Osamu Motojima welcomed the participants, outlined the key priorities of the Unique ITER Team in relation to ITER construction, and underlined the major physics R&D needs. David Campbell, director of the Plasma Operation Directorate, gave an overview on the issues of physics R&D that are critical to the design and development of the ITER Research Plan.

Among these priorities are: the understanding and control of Edge Localized Modes (ELMs); disruptions and runaway electrons (and their mitigation); H-mode accessibility; use of all-metal plasma-facing components; the behaviour of tungsten impurities; tritium retention; dust; and power scrape-off layer (SOL) thickness.

The chairs of the seven ITPA Topical Groups reviewed the progress made in 2012 and proposed an experiment plan for 2013, focusing on the urgent issues for ITER. The Chair of Divertor and SOL Physics Topical Group, Emmanuelle Tsitrone, coordinated a special discussion session on the plan for joint research focusing on the comparison of divertors with carbon and tungsten plasma-facing components.

On the basis of high-priority research topics for ITER and the experimental capabilities of current fusion facilities, the facility program leaders decided on the priorities for each proposed experiment within their experimental programs for 2013. David Campbell commented, „I would like to thank ITPA for the continuing support of ITER R&D activities. We regard ITPA as a very important component of the ITER project and a critical part of our physics R&D program, providing a great deal of input to the physics design basis for the completion of the ITER design—a high-priority activity at the moment.”

CODAC also works on KSTAR

Recently the standard ITER CODAC (Control, Data Access and Communication) technologies successfully demonstrated their adaptability and operability for tokamak control at the Korea Superconducting Tokamak Advanced Research (KSTAR), in operation since 2008.

Like ITER CODAC, the KSTAR control system is using EPICS as middleware for tokamak control and operation. Therefore, KSTAR is a natural target for evaluating and validating CODAC technologies as has been identified in the Memorandum of Understanding between ITER Organization and National Fusion Research Institute (NFRI).

During the last 15 months, the KSTAR control team has implemented a duplication of the fuel control system and a part of the plasma control system using CODAC technologies (standardized hardware and CODAC Core System). On July 26th, 2012, a first test was successfully executed by injecting deuterium gas into the vacuum vessel based on pre-configured waveforms from the plasma control system.

The project will be completed in November by using real density signals from a millimetre-wave interferometer and closing the density feedback control loop during the KSTAR plasma operation.

The KSTAR fuelling system operates with four different gases for plasma creation, wall cleaning and diagnostics. For the experiment, one piezo-electric valve (for deuterium gas) was selected as an actuator. Various pre-configured patterns were used as reference inputs to the plasma control system (PCS) for controlling the fuel injection. The PCS was implemented on a high performance computer using ATCA form factor, CODAC standard real-time operating system (MRG-R) and MARTe real-time framework originally developed at JET.

The density signal was simulated by programmable waveforms. A CODAC standard fast controller (fuel controller) was also implemented to control the embedded piezo-valve controller and to acquire diagnostics signals such as vacuum vessel pressure, gas flow, valve drive voltage, etc. at 10 kHz. The plasma control system communicated with the fuel controller over the standard CODAC real time network at 1 kHz.

As the measurements from the first test showed identical results as the KSTAR fuelling system, it was confirmed that the technologies adopted or being considered for ITER CODAC were applicable for the plant control at tokamak, that is, CODAC is heading in the right direction.


Written procedures are her game

As an international organization—and one applying for nuclear licensing in France—ITER is required to have a well-documented management system, with approved procedures describing the process flow for every area of the project.

Since 2008, the Quality Assurance Division has been developing the Management and Quality Program (MQP), a process-based system that organizes ITER’s management documents into a structure governing relations, procedures, and working instructions.

„The written procedures contained in the MQP program basically instruct end users how to do their work,” says Florence Tadjer, who joined the Division in April. „But of course it is not enough that these documents exist: they must also be well understood and applied throughout the project.”

As MQP Liaison Officer for the Administration and Plasma Operation Directorates, Florence will work in an advisory role with process „owners” on management documents, ensuring that the proper rules are followed to write documents, and deciding whether the document contains the type of guidelines that should be incorporated into the MQP framework or not. „In fact, not every departmental document needs to be part of the MQP,” says Florence. „On the other hand, it is also my role to identify those documents that should be incorporated.”

Florence comes to ITER from the International Atomic Energy Agency (IAEA), where she was a quality manager in the laboratory responsible for analyzing safeguard samples from nuclear facilities. It was her responsibility to maintain the laboratory’s quality certification by updating the quality management system and conducting regular audits in order to make sure that the quality system was well implemented in all areas of the laboratory.

„Training and auditing are part of the quality manager’s job,” insists Florence. At ITER, the team of Liaison Officers will work to improve the MQP documentation, and expend a lot of effort to communicate about the program and make sure that training is offered on the implementation of the system.

„ITER is a young organization and things are still evolving. A lot remains to be done and I know I’ll enjoy the lack of routine!"


India signs two R&D contracts

The Indian Domestic Agency has signed two contracts for the development of the Radio Frequency (RF) sources forming part of ITER’s Ion Cyclotron Heating and Current Drive (IC H&CD) system. The contracts were signed with the American company Continental Electronics Corporation and with Thales Electron Devices, France.

The IC H&CD system is one of the major tools for achieving the plasma performances foreseen in ITER’s operation scenarios. This system is designed to provide 20 MW into the plasma, at frequencies included in the band 40 MHz to 55 MHz. ITER India is in charge of the procurement of the RF sources subsystem and the corresponding Procurement Arrangement was signed in February 2010. A total of nine RF sources will be provided: eight sources used for plasma operation, plus one spare.

For ensuring 20 MW power availability for plasma operation, 24 MW is required at the output of the transmitter at frequencies up to 65 MHz. As there is no unique amplifier chain able to meet the output power specifications, the layout consists of two parallel four-stage amplifier chains, with a combiner circuit on the output side. This configuration is used in ASDEX upgrade ICRF facilities since 1998.

Each amplifier chain is made of a wide band solid state amplifier cascaded to a three tube based tuned amplifier: a pre-driver, followed by a driver stage and a final stage. But, even in this configuration, the final stage tubes have to achieve challenging power levels.

Only two suppliers worldwide are able to reach the target. In order to identify the best and most reliable technology for building this amplifier chain, R&D contracts were signed with both companies. Results are expected by the end of next year followed by the Preliminary Design Review.