What’s Happening in Fusion

Research aimed at harnessing nuclear fusion as a long-term solution to our energy supply continues worldwide, with some major developments expected in the very near term. A collaboration of nations is nearing agreement to proceed with an international fusion project of unprecedented scale to harness the promise of fusion energy, the same form of energy that powers the sun.

In fusion, nuclei of light atoms are fused together to form a new element of slightly less mass. The “missing” mass is converted into energy, as predicted by Einstein’s famous formula, E=mc2.. The most attractive reaction involves the fusion of deuterium (D) and tritium (T) ions which releases 17.6 MeV in the form of a neutron at 14.1 MeV and a helium ion (alpha particle) at 3.5 MeV, with an energy gain ~ 500. For power production, the challenge is to produce a “burning plasma” where enough ions are confined at sufficient density and temperature such that the heat from the alpha particles can maintain the plasma without significant auxiliary heating power.

One measure of the performance of a plasma is the ratio “Q” of fusion output power produced to auxiliary heating power input. A major step was achieved in the early 1990’s when fusion devices achieved Q ~ 1 conditions referred to as “breakeven,” where the fusion power production reached the level of heating power input. Three devices entered this domain, namely the Tokamak Fusion Test Reactor (TFTR) in Princeton, the Joint European Torus (JET) in England, and the Japanese Tokamak 60 m3 (JT-60) in Japan. For example, the TFTR succeeded in producing controlled D-T reactions yielding pulses of ~ 10 MW of fusion power lasting for a few seconds at a time. The TFTR, JET, and JT-60 machines were the result of ~ $0.5B investments made by each of the host countries in the late 70’s, as public interest in energy R&D reached a peak.

The next major step in the program is to enter the burning plasma domain where the alpha particle power begins to surpass the auxiliary power. Since the alpha energy is roughly 1/5 of the energy released per D-T reaction, and since Q is defined as the ratio of fusion power to heating power, the alpha particle heating becomes dominant when Q>5.

The design and construction of a burning plasma fusion machine is a major scientific and engineering challenge. The device itself will be of the same scale as a large electric power generating station with a cost ~ $5.0B. The scale of such an endeavor, the tradition of collaboration between nations in fusion research, along with the vital implications for the future of mankind all suggest an international project.

Indeed, the next major fusion project on the horizon is the International Thermonuclear Experimental Reactor (ITER). The idea of ITER was born as an initiative at the 1985 Geneva Summit between the US and the USSR. President Reagan and General Secretary Gorbachev began a process that led to a collaboration among the European Union, Japan, Russia (initially the Soviet Union) and the US, to design and carry out the supporting research and development for ITER, whose programmatic objective is “to demonstrate the scientific and technological feasibility of fusion energy for peaceful purposes.”

From the beginning of the formal collaboration in 1988 through the completion of the initial six-year agreement for the ITER Engineering Design Activities (EDA), the US was an equal party to the ITER effort, carrying out significant tasks in design and supporting R&D. However, with support for “big science” waning, in 1998, the Congress directed the DOE to conduct an orderly closeout of its ITER activities, which was done during FY1999. Meanwhile, work continued by the European, Japanese, and Russian teams in developing a more cost effective design.

In January 2003, President Bush committed the U.S. to join the ITER negotiations, noting that “the results of ITER will advance the effort to produce clean, safe, renewable, and commercially available fusion energy by the middle of this century. Commercialization of fusion has the potential to dramatically improve America’s energy security while significantly reducing air pollution and emissions of greenhouse gases.”
Momentum has been building since the US announced its intention to re-join the project, and the ITER Parties have negotiated an understanding on sharing the cost of ITER, on allocating the hardware procurements, and on most of the terms and conditions of a formal agreement. Additional developments include the addition of China and Korea to the roster of participating nations.

The site decision remains to be completed, but has been narrowed down to two locations, one in Cadarache, France, and the other in Rokassho, Japan. A final decision is imminent. However, legislative bodies in the various countries must still appropriate funds for actual construction before the project can move forward. The Parties hope to begin construction in 2006, with completion in 2014.

International Thermonuclear
Experimental Reactor

The ITER machine (http://www.iter.org/) utilizes a magnetic confinement system called a “tokamak,” a toroidal (doughnut-shaped) configuration which contains the hot plasma in a “magnetic bottle.” The plasma is fueled and heated to reach a high power amplification (Q) burn of deuterium-tritium (D-T). Pulse lengths up to 300 s can be achieved using inductive current drive via the poloidal field coils, primarily the central solenoid. The heating systems and other noninductive current sources can be further used to drive the plasma current, extending the nominal pulse-length of 300 s up to steady state. Plasma control is provided by the poloidal field system, and the pumping, fueling and heating systems, based on feedback from diagnostic sensors.

The major tokamak components are the superconducting toroidal and poloidal field coils which magnetically confine, shape and control the plasma inside the toroidal vacuum vessel. The internal, removable components, including blanket modules, divertor cassettes, and port plugs for the plasma limiter, heating antennae, test blanket modules and diagnostics sensors, absorb most of the heat from the plasma and protect the vessel and magnet coils from excessive nuclear radiation. The divertor exhausts the helium from the fusion reaction and limits the concentration of impurities in the plasma. The heat deposited in the components is rejected to the environment via the cooling water system. The tokamak is housed in a cryostat, with thermal shields between the hot parts and the magnets and support structures which are at cryogenic temperature. Successive barriers are provided for tritium (and activated dust). These include the vacuum vessel, the cryostat, and active air conditioning systems, with detritiation and filtering capability in the building. Under normal operation of ITER, the additional radioactive dose to any member of the public will be below 1% of natural background. Under the worst imaginable sequence of events, the additional radioactive dose to any member of the public will be below natural background. Even in hypothetical situations, no member of the public will need to be evacuated for technical reasons.

Since the start of the EDA, $920M (year 2000 values) have been spent on technology R&D, mostly on seven large R&D projects (toroidal field and central solenoid model coils, vessel, blanket and divertor models, and blanket and divertor remote handling), to give confidence in the manufacturing capability to build ITER, and in the safe and reliable operation of components. Direct capital costs for ITER have been estimated at $3800M. Staff and R&D costs during construction add a further $760M. Operation costs will be ~$260M/annum, and decommissioning will cost ~$470M.
Although the ITER Project has strong momentum now and a good chance of moving forward, contingency plans exist in the US for an alternate approach to achieving a burning plasma via a machine called the Fusion Ignition Research Experiment (FIRE). The FIRE machine (http://fire.pppl.gov/) would utilize liquid nitrogen cooled copper magnets instead of superconductors, and could produce a burning plasma on a smaller scale than the ITER machine.

Additional research at various laboratories around the world aims to enhance the scientific understanding of plasma behavior, to provide input to the ITER design process, and to identify alternate configurations which could lead to more economical fusion energy in the future. Major projects in the US include the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory (http://nstx.pppl.gov/), the Doublet (DIIID) device at General Atomics in San Diego, CA (http://www.gat.com/), and the Alcator C-Mod device at MIT in Cambridge, MA (http://www.psfc.mit.edu/cmod/).

In summary, fusion energy shows great promise to contribute to securing the energy future of humanity. The risk of conflicts arising from energy shortages and supply cutoffs, as well as the risk of severe environmental impacts from existing methods of energy production, are strong reasons to pursue fusion energy now. The world effort to develop fusion energy is at the threshold of a new stage in its research: the investigation of burning plasmas. This investigation, at the frontier of the physics of complex systems, would be a huge step in establishing the potential of magnetic fusion energy to contribute to the world’s energy security. There is an overwhelming consensus among fusion scientists that we are now ready scientifically, and have the full technical capability, to embark on this step. The fusion community is prepared to construct a facility that will allow us to produce this new plasma state in the laboratory, uncover the new physics associated with the fusion burn, and develop and test new technology essential for fusion power.

With a decision on ITER, fusion research will move into a new era which will hopefully reinvigorate the US program. In fact the attendance at the IEEE/NPSS Symposium on Fusion Engineering (SOFE) is a good measure of the health of the program, which has been in decline during the last decade due in part to the impasse over ITER. The fusion community is hopeful that this trend will reverse now, and the impact of ITER will be evident by the time of the 21st SOFE to be held in Knoxville, Tennessee in September 2005.

Charles Neumeyer is a member of the IEEE/NPSS AdCom representing Fusion Technology. He can be reached at the Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543-0451; Phone: +1 609 243-2159; E-mail: cneumeyer@pppl.gov.