ADITYA: a little Sun

Alcator C-Mod: Training future physicists on a high-field tokamak

The Plasma Science and Fusion Center at the Massachusetts Institute of Technology (MIT) in the US is home to Alcator C-Mod, a compact tokamak capable of high magnetic field and dense, well-confined plasmas.

Research on Alcator C-Mod focuses on divertor physics; detecting disruptions and minimizing consequences for present and future tokamaks; plasma control; the optimization of radio frequency heating; microwave current drive and its role in suppressing turbulence and increasing confinement; full exploration of an all-metal divertor target, including erosion; and diagnostics.

As the largest university-based facility in the US, Alcator C-Mod plays an important role in training the next generation of plasma scientists.

Read more about Alcator C-Mod here.

ASDEX Upgrade: Investigating plasma stability and plasma-wall interaction

At the original ASDEX tokamak at the Max Planck Institute of Plasma Physics in Germany, an important discovery for tokamak operation was made in 1982: H-mode. This optimum, high-confinement operating mode has become the basis for advanced tokamak operation, including ITER.

Since 1991, ASDEX Upgrade has operated as a midsize experiment whose essential plasma properties—particularly plasma density, plasma pressure, and wall load—have been adapted to the conditions that will be present in future fusion power plants.

With a power-plant-like geometry, a tungsten-clad vessel wall, and powerful and flexible plasma heating, ASDEX Upgrade contributes to the preparation of ITER and DEMO through studies focused on plasma-wall interactions and plasma stability. Two years of experimentation with the tungsten wall, for example, contributed to the ITER decision to install a tungsten divertor from the start of operations.

Read more about ASDEX Upgrade here. (Photo: IPP; Volker Rohde)

DIII-D: Exploring key ITER physics issues and advanced operation scenarios

The DIII-D advanced tokamak was developed by General Atomics in San Diego (US) as part of the international effort to achieve magnetically confined fusion. The mission of the DIII-D research program is to establish the scientific basis for the optimization of the tokamak approach to fusion energy production.

In operation since the 1980s, DIII-D played an important role in providing data for the engineering design phase of ITER, a machine that incorporates many DIII-D features. DIII-D pioneered key fusion technology, including the use of beams of neutral particles for plasma heating and resonant magnetic perturbation (RMP) coils to suppress plasma instabilities called Edge Localized Modes (ELMs). DIII-D is currently exploring a wide range of scientific issues which will assist in optimizing ITER operation.

These include: exploration of the effect that internal stabilization coils have on preventing energy bursts from the plasma edge; development of high-power microwave transmission line components with low energy losses; and work on software for controlling the plasma and protecting the ITER machine.

Read more about the DIII-D advanced tokamak here.

EAST: Addressing the physics and technology issues of steady-state operation

First plasma was achieved in 2006 on the fully superconducting Experimental Advanced Superconducting Tokamak (EAST) at the Institute of Plasma Physics in Hefei, China.

Since then, EAST has been upgraded with augmented auxiliary heating and operational capabilities and now operates with ITER-like magnetic configurations and heating schemes, allowing the exploration of plasmas over long timescales.

Research at EAST on physics and technology issues under steady-state operational conditions is directly relevant to ITER. Recent experiments have demonstrated the sustainment of high temperature plasmas in H-mode (see ASDEX-Upgrade) over a record timescale of more than 30 seconds, achieved by heating the plasma with radio-frequency waves such as lower hybrid waves.

These results also suggested a potent new method for suppressing ELMs (see DIII-D) with radio waves. Scientists are also pursuing investigations of plasma-wall interactions on EAST under stationary conditions, exploiting the long-pulse capabilities of the machine's superconducting magnet systems.

Read more about the EAST tokamak here.

JET: An ITER-like wall and experiments with tritium

The Joint European Torus (JET), located at Culham Centre for Fusion Energy in the UK, is the world's largest and most powerful tokamak in operation today and the focal point of European fusion research.

Designed to study fusion in conditions approaching those needed for a power plant, it is the only device that can handle the deuterium-tritium fuel mix that will be used in ITER (and in later fusion power plants). In operation since 1983, milestones at JET have included the world's first controlled release of deuterium-tritium fusion power (1991) and the world record for fusion power (16 megawatts in 1997).

In recent years, the program's primary task has been to prepare for the construction and operation of ITER by acting as a test bed for ITER technologies and plasma operating scenarios:

* upgraded with an ITER-like beryllium and tungsten wall and additional heating power, JET enables scientists to develop plasma scenarios that resemble as closely as possible those planned for ITER, investigate the interaction of the plasma with wall materials, and study the accumulation of tungsten from the wall in the plasma core;

* experiments to characterize the melting behaviour of tungsten run on the JET divertor provided valuable physics data input for the ITER divertor strategy (the choice to install a tungsten divertor from the start) and continue to inform divertor physics in advance of ITER operation;

* with ITER-like regimes of plasma operation, scientists have the opportunity to study plasma instabilities such as ELMs (see DIII-D) and develop methods to predict and mitigate these instabilities;

* current plans for JET foresee a scientific campaign with deuterium-tritium (D-T) plasmas in 2017. These experiments (the first to use tritium at JET since 2003) will act as an important "dress rehearsal" in preparation for ITER's operation with tritium.

The European Consortium for the Development of Fusion Energy, EUROfusion, provides the work platform to exploit JET.

Read more on JET here.

JT-60SA: Thinking ahead to the optimization of fusion power plants

The Satellite Tokamak Program, JT-60SA, is a major modification of the existing JT-60U tokamak at the Naka Fusion Institute in Japan. Part of the Broader Approach Agreement signed between Japan and Euratom (and implemented by the Japan Atomic Energy Agency and the European Domestic Agency for ITER), it is designed to support the operation of ITER and to investigate how best to optimize the design and operation of fusion power plants built after ITER.

When it comes on line at the end of this decade after a six-year assembly and commissioning period, the JT-60SA research program will investigate critical areas of plasma physics, fusion engineering and theoretical models and simulation codes. These include the development of optimized operational regimes; questions of stability and control, transport and confinement, and high-energy particle behaviour; pedestal and edge physics; plasma-material interaction; fusion engineering; and theoretical models and simulation codes.

Read more about the JT-60SA upgrade project here.

KSTAR: A pilot device for ITER

KSTAR—short for Korea Superconducting Tokamak Advanced Research—joined the ranks of superconducting tokamaks when it achieved first plasma in 2008 after 11 years of construction at the National Fusion Research Institute in Daejon.

Through long-pulse operation, the machine is capable of contributing to the investigation of the plasma physics of future steady-state fusion power plants.

Standard ITER CODAC (Control, Data Access and Communication) technologies have been tested in advance on KSTAR, successfully demonstrating their adaptability and operability for tokamak control.

Characteristics of the machine's superconducting magnet and cryogenic systems also provide valuable data to the design and operation of ITER in terms of quality control and assurance for fabrication and assembly.

KSTAR will be utilized as a test bed for the 170 GHz gyrotron and the 5 GHz klystron for ITER's electron cyclotron heating and lower hybrid current drive. Since 2011, scientists have achieved successful results in the mitigation of ELMs, using techniques previously demonstrated on DIII-D and Asdex Upgrade.

Read more on KSTAR here.

MAST: A spherical tokamak to test plasma regimes

Since being commissioned in 2000, the Mega Amp Spherical Tokamak MAST has made significant contributions to fusion physics, particularly in understanding the instabilities that form at the edges of the plasma.

Run by the Culham Centre for Fusion Energy (CCFE) in the UK, MAST is currently undergoing an upgrade to investigate the super-X divertor—a magnetic configuration that spreads the heat loads at the divertor area of the machine.

Other features of the upgrade include an increase in the pulse length by a factor approaching ten, additional heating power, and better control and pumping capacities to contain the resulting higher temperature, longer-pulse plasmas.

Future reactors must run for hours or days rather than the seconds of today's devices. The MAST Upgrade will allow scientists to study plasmas that approach this operational mode, known as "steady-state."

Read more about the MAST upgrade here.

NSTX-U: Contributing to the studies of plasma behaviour

The National Spherical Torus Experiment (NSTX), in operation since 1999 at the Princeton Plasma Physics Laboratory in the US (New Jersey), is a magnetic fusion device that, like MAST, is based on the spherical tokamak concept.

A major upgrade was completed in 2016 that has doubled the strength of both its electric current and magnetic fields. Research at NSTX-U will contribute to understanding how the plasma will behave and perform in ITER.

Experiments on the revamped NSTX-U, with its new central solenoid, additional neutral beam injector and reinforced structure, will allow scientists to investigate the cause of plasma disruptions, advance toroidal confinement physics predictive capabilities, and study the effect of increased power flux on wall materials.

Read more on NSTX-U here.

SST-1: Joining the ranks of superconducting research tokamaks

The Indian Steady State Superconducting Tokamak (SST-1) was fully commissioned in 2013. Located at the Institute for Plasma Research in Gujarat, India, SST-1 produces repeatable plasma discharges up to ~ 500 ms with plasma currents in excess of 75000 A at a central field of 1.5 T.

SST-1 routinely operates with an ITER-like electric field of ~ 0.35 V/m assisted by electron cyclotron resonance pre-ionizations in both fundamental and second harmonic modes. The SST-1 plasma carries all the standard attributes of tokamak plasma in contemporary devices. SST-1 is also the only tokamak in the world with superconducting toroidal field magnets operating in two-phase helium instead of supercritical helium in a cryo-stable manner, thereby demonstrating reduced cold helium consumption.

SST-1 is now preparing for steady state plasma experiments with the installation of plasma-facing components. Its objectives will be to study feedback and control, divertor operation, and plasma-wall interactions in steady state plasmas.

Read more about SST-1 here.

T-15U: Determining optimal reactor parameters

The superconducting T-15 tokamak was operated from 1988 to 1995 at the Kurchatov Institute in Moscow, Russia.

Today, the tokamak is being upgraded with the auxiliary plasma heating and current drive systems, which will allow the simultaneous achievement of high plasma temperature and plasma density.

The systems—which include three neutral beam injectors, electron cyclotron resonance heating (seven gyrotrons), ion cyclotron resonance heating (three antennas) and low hybrid heating and current drive with pulse duration up to 30 s—will be used to control plasma parameters profiles.

Research on the T-15U will support ITER, DEMO and fusion neutron source planning and operation and will contribute to the determination of optimal parameters for future fusion reactors and for solving problems in atomic power engineering.

(no website is currently available)

TCV: Versatility for the study of differently shaped plasmas and localized heating

TCV is a variable configuration tokamak for the study of differently shaped cross-sections of the plasma run by the Swiss Plasma Center of the EPFL (Ecole Polytechnique Fédérale de Lausanne) in Lausanne.

The mission of the TCV program is to apply its highly specialized capabilities (plasma shaping, versatile electron cyclotron heating, measurement and control systems) to the exploration of the physics of magnetically confined plasmas. TCV supports ITER and also explores the way to a prototype fusion reactor.

In 2014, TCV underwent a major upgrade in heating power with the installation of a 1MW neutral beam injection system.

Read more about TCV here.

TORE SUPRA/WEST: Minimizing the risks of a tungsten divertor

Tore Supra is a superconducting tokamak that has been in operation at the Institute for Magnetic Fusion Research (CEA Cadarache, southern France) since 1988.

It was the first tokamak to successfully implement superconducting magnets and actively-cooled plasma-facing components, and has specialized in the physics exploration of long-duration plasma pulses, reaching a record of 6.5 minutes in December 2003.

Today, some 46,000 plasma shots later, Tore Supra is being reconfigured as a test bed for ITER. With a new, actively-cooled tungsten divertor, it will test tungsten technology, acquire data on metal fatigue, and explore the components' boundary conditions in advance of ITER. The project, called WEST for "W Environment in Steady-state Tokamak" (where W is the chemical symbol for tungsten), got off to a start in 2009.

As early as 2016, the machine will be ready to test the first samples of plasma-facing units—an arrangement of small tungsten blocks that, once assembled, will form the new divertor.

Read more about WEST here.